概述
Activity的启动方式有两种，一种是显式的，一种是隐式的。
而且，启动的 Activity 和原 Activity 的进程关系的不同又可以分为两种情况，一种是在同一个进程，另外一种情况是开启一个新的进程来启动 Activity。
Activity启动之前的一些事情
- init进程：init是所有linux程序的起点，是Zygote的父进程。解析init.rc孵化出Zygote进程。
- Zygote进程：Zygote是所有Java进程的父进程，所有的App进程都是由Zygote进程fork生成的。
- SystemServer进程：System Server是Zygote孵化的第一个进程。SystemServer负责启动和管理整个Java framework，包含AMS，PMS等服务。
- Launcher：Zygote进程孵化的第一个App进程是Launcher。
1.init进程是什么？
Android是基于linux系统的，手机开机之后，linux内核进行加载。加载完成之后会启动init进程。
init进程会启动ServiceManager，孵化一些守护进程，并解析init.rc孵化Zygote进程。
2.Zygote进程是什么？
所有的App进程都是由Zygote进程fork生成的，包括SystemServer进程。Zygote初始化后，会注册一个等待接受消息的 socket，OS层会采用socket进行IPC通信。
3.为什么是Zygote来孵化进程，而不是新建进程呢？
每个应用程序都是运行在各自的Dalvik虚拟机中，应用程序每次运行都要重新初始化和启动虚拟机，这个过程会耗费很长时间。Zygote会把已经运行的虚拟机的代码和内存信息共享，起到一个预加载资源和类的作用，从而缩短启动时间。
Activity启动阶段
涉及到的概念
- 进程：Android系统为每个APP分配至少一个进程
- IPC：跨进程通信，Android中采用Binder机制。
涉及到的类
- ActivityThread：代表了应用的主线程，在Activity.attach()方法中初始化
- TaskRecord：Activity的管理者
- ActivityStack：Stack的管理者
- ActivityStackSupervisor：ActivityStack的管理者，早期的Android版本是没有这个类的，直到Android 6.0才出现。
涉及到的进程
- Launcher所在的进程
- AMS所在的SystemServer进程
- 要启动的Activity所在的app进程
如果是启动根Activity，就涉及上述三个进程。
如果是启动子Activity，那么就只涉及AMS进程和app所在进程。
具体流程
- Launcher：Launcher通知AMS要启动activity。
startActivitySafely->startActivity->Instrumentation.execStartActivity()(AMP.startActivity)->AMS.startActivity
- AMS:PMS的resoveIntent验证要启动activity是否匹配。
如果匹配，通过ApplicationThread发消息给Launcher所在的主线程，暂停当前Activity(Launcher);
- 暂停完，在该activity还不可见时，通知AMS，根据要启动的Activity配置ActivityStack。然后判断要启动的Activity进程是否存在?
存在：发送消息LAUNCH_ACTIVITY给需要启动的Activity主线程，执行handleLaunchActivity
不存在：通过socket向zygote请求创建进程。进程启动后，ActivityThread.attach
- 判断Application是否存在，若不存在，通过LoadApk.makeApplication创建一个。在主线程中通过thread.attach方法来关联ApplicationThread。
- 在通过ActivityStackSupervisor来获取当前需要显示的ActivityStack。
- 继续通过ApplicationThread来发送消息给主线程的Handler来启动Activity（handleLaunchActivity）。
- handleLauchActivity：调用了performLauchActivity，里边Instrumentation生成了新的activity对象，继续调用activity生命周期。
IPC过程：
双方都是通过对方的代理对象来进行通信。
- 1.app和AMS通信：app通过本进程的AMP和AMS进行Binder通信
- 2.AMS和新app通信：通过ApplicationThreadProxy来通信，并不直接和ActivityThread通信
Activity启动流程（从Launcher开始）：
第一阶段： Launcher通知AMS要启动新的Activity（在Launcher所在的进程执行）
- Launcher.startActivitySafely //首先Launcher发起启动Activity的请求
- Activity.startActivity
@Override
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
// Note we want to go through this call for compatibility with
// applications that may have overridden the method.
startActivityForResult(intent, -1);
}
}
- Activity.startActivityForResult
public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {
// 一般情况下会走mParent == null分支
if (mParent == null) {
//调用Instrumentation.execStartActivity()启动新的Activity。mMainThread类型为ActivityThread, 在attach()函数被回调时被赋值。
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
if (ar != null) {
// 如果activity之前已经启动，而且处于阻塞状态，execStartActivity函数直接返回要启动的activity的result或者null。
//如果结果不为空，发送结果
mMainThread.sendActivityResult(
mToken, mEmbeddedID, requestCode, ar.getResultCode(),
ar.getResultData());
}
if (requestCode >= 0) {
// 如果需要一个返回结果，那么赋值mStartedActivity为true，在结果返回来之前保持当前Activity不可见
mStartedActivity = true;
}
cancelInputsAndStartExitTransition(options);
} else {
if (options != null) {
mParent.startActivityFromChild(this, intent, requestCode, options);
} else {
mParent.startActivityFromChild(this, intent, requestCode);
}
}
}
这里注意到 mParent 变量，一般情况下这里 mParent 是为空的，除非是启动 ActivityGroup 等可以嵌套 Activity 的内部的 Activity 时才会不为空。
- Instrumentation.execStartActivity //交由Instrumentation代为发起请求
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
Uri referrer = target != null ? target.onProvideReferrer() : null;
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
// 判断mActivityMonitors是否为空，mActivityMonitors可以通过addMonitor()方法创建，一般在自动化测试时使用
// 一般情况下不会走这个分支
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
if (am.match(who, null, intent)) {
am.mHits++;
// 如果处于阻塞状态，直接返回
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess();
// 这里的ActivityManagerNative.getDefault返回ActivityManagerService的远程接口，即ActivityManagerProxy接口
// 由它通过进程间通信调用 AMS 的 startActivity 方法
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
mActivityMonitors 是 ActivityMonitor 的一个集合，该类用来监控应用中的单个活动，可监控一些指定的意图。一般在一些测试Case时使用。创建 ActivityMonitor 实例后，通过调用 ActivityInstrumentationTestCase2 的 getInstrumentation() 方法获取 Instrumentation 实例，然后通过 addMonitor 方法添加这个实例，当目标活动启动后，系统会匹配 Instrumentation 中的 ActivityMonitor 实例列表，如果匹配，就会累加计数器。
- ActivityManager.getService().startActivity //通过IActivityManagerSingleton.get()得到一个AMP代理对象
- ActivityManagerProxy.startActivity //通过AMP代理通知AMS启动activity
第二阶段：AMS先校验一下Activity的正确性，如果正确的话，会暂存一下Activity的信息。然后，AMS会通知Launcher程序pause Activity（在AMS所在进程执行）
- ActivityManagerService.startActivity
@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
- ActivityManagerService.startActivityAsUser
@Override
public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {
enforceNotIsolatedCaller("startActivity");
userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
false, ALLOW_FULL_ONLY, "startActivity", null);
return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, options, false, userId, null, null);
}
从这里开始就在AMS进程中执行了，下面简单介绍一下这些参数代表的意义：
resultTo： 指调用者Activity的mToken，mToken对象保存它所处的ActivityRecord信息
- ActivityStackSupervisor.startActivityMayWait
final int startActivityMayWait(IApplicationThread caller, int callingUid,
String callingPackage, Intent intent, String resolvedType,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, WaitResult outResult, Configuration config,
Bundle options, boolean ignoreTargetSecurity, int userId,
IActivityContainer iContainer, TaskRecord inTask) {
// 不允许传递文件描述符
if (intent != null && intent.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
boolean componentSpecified = intent.getComponent() != null;
// 重新实例化一个Intent对象，防止对intent的修改
intent = new Intent(intent);
// 通过Intent解析Activity信息，最终会调用PackageManagerService.resolveIntent()来查询和选择相关的Activity
// 如果有多个Activity匹配，那么就会弹框让用户来选择，这部分分析此处省略
ActivityInfo aInfo =
resolveActivity(intent, resolvedType, startFlags, profilerInfo, userId);
ActivityContainer container = (ActivityContainer)iContainer;
synchronized (mService) {
// 一般情况下container 为null
if (container != null && container.mParentActivity != null &&
container.mParentActivity.state != RESUMED) {
return ActivityManager.START_CANCELED;
}
final int realCallingPid = Binder.getCallingPid();
final int realCallingUid = Binder.getCallingUid();
int callingPid;
if (callingUid >= 0) {
callingPid = -1;
} else if (caller == null) {
callingPid = realCallingPid;
callingUid = realCallingUid;
} else {
callingPid = callingUid = -1;
}
final ActivityStack stack;
if (container == null || container.mStack.isOnHomeDisplay()) {
// 一般会走到这里，将当前的ActivityStack赋值给stack
stack = mFocusedStack;
} else {
stack = container.mStack;
}
stack.mConfigWillChange = config != null && mService.mConfiguration.diff(config) != 0;
final long origId = Binder.clearCallingIdentity();
if (aInfo != null &&
(aInfo.applicationInfo.privateFlags
&ApplicationInfo.PRIVATE_FLAG_CANT_SAVE_STATE) != 0) {
// 处理heavy-weight process，即重量级进程，这种进程在内存不足时不会被kill掉
// 一般不会走这里
if (aInfo.processName.equals(aInfo.applicationInfo.packageName)) {
if (mService.mHeavyWeightProcess != null &&
(mService.mHeavyWeightProcess.info.uid != aInfo.applicationInfo.uid ||
!mService.mHeavyWeightProcess.processName.equals(aInfo.processName))) {
int appCallingUid = callingUid;
…………//此处代码省略
}
}
}
int res = startActivityLocked(caller, intent, resolvedType, aInfo,
voiceSession, voiceInteractor, resultTo, resultWho,
requestCode, callingPid, callingUid, callingPackage,
realCallingPid, realCallingUid, startFlags, options, ignoreTargetSecurity,
componentSpecified, null, container, inTask);
Binder.restoreCallingIdentity(origId);
if (stack.mConfigWillChange) {
// 一般不会走这里
…………
}
if (outResult != null) {
// 一般不会走这里
……
}
return res;
}
}
- ActivityStackSupervisor.startActivityLocked ：检查有没有在AndroidManifest中注册
final int startActivityLocked(IApplicationThread caller,
Intent intent, String resolvedType, ActivityInfo aInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode,
int callingPid, int callingUid, String callingPackage,
int realCallingPid, int realCallingUid, int startFlags, Bundle options,
boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,
ActivityContainer container, TaskRecord inTask) {
int err = ActivityManager.START_SUCCESS;
ProcessRecord callerApp = null;
if (caller != null) {
// 获取调用者所在的ProcessRecord
callerApp = mService.getRecordForAppLocked(caller);
if (callerApp != null) {
callingPid = callerApp.pid;
callingUid = callerApp.info.uid;
} else {
err = ActivityManager.START_PERMISSION_DENIED;
}
}
// 获取userId，如果是管理员用户该值为0
final int userId = aInfo != null ? UserHandle.getUserId(aInfo.applicationInfo.uid) : 0;
if (err == ActivityManager.START_SUCCESS) {
// 打印一些信息
}
ActivityRecord sourceRecord = null;
ActivityRecord resultRecord = null;
// resultTo为调用者Activity的mToken，保存了它所处的ActivityRecord信息
if (resultTo != null) {
// 获取调用者Activity所对用的ActivityRecord
sourceRecord = isInAnyStackLocked(resultTo);
if (sourceRecord != null) {
// 如果需要返回结果，即requestCode不为-1，赋值resultRecord
if (requestCode >= 0 && !sourceRecord.finishing) {
resultRecord = sourceRecord;
}
}
}
final int launchFlags = intent.getFlags();
if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {
// 对Intent.FLAG_ACTIVITY_FORWARD_RESULT处理，如果设置了这个flag，执行结果相当于透传
// 比如Activity启动顺序A->B->C，那么C的结果将直接返回给A
…………//此处代码忽略
}
if (err == ActivityManager.START_SUCCESS && intent.getComponent() == null) {
err = ActivityManager.START_INTENT_NOT_RESOLVED;
}
if (err == ActivityManager.START_SUCCESS && aInfo == null) {
// 如果待启动的Activity没有在Manifestfest中显示声明，就会有这个error
err = ActivityManager.START_CLASS_NOT_FOUND;
}
if (err == ActivityManager.START_SUCCESS
&& !isCurrentProfileLocked(userId)
&& (aInfo.flags & FLAG_SHOW_FOR_ALL_USERS) == 0) {
err = ActivityManager.START_NOT_CURRENT_USER_ACTIVITY;
}
if (err == ActivityManager.START_SUCCESS && sourceRecord != null
&& sourceRecord.task.voiceSession != null) {
……
}
if (err == ActivityManager.START_SUCCESS && voiceSession != null) {
……
}
final ActivityStack resultStack = resultRecord == null ? null : resultRecord.task.stack;
if (err != ActivityManager.START_SUCCESS) {
if (resultRecord != null) {
resultStack.sendActivityResultLocked(-1,
resultRecord, resultWho, requestCode,
Activity.RESULT_CANCELED, null);
}
ActivityOptions.abort(options);
return err;
}
boolean abort = false;
final int startAnyPerm = mService.checkPermission(
START_ANY_ACTIVITY, callingPid, callingUid);
执行一系列的权限检查
…………
abort |= !mService.mIntentFirewall.checkStartActivity(intent, callingUid,
callingPid, resolvedType, aInfo.applicationInfo);
if (mService.mController != null) {
try {
// The Intent we give to the watcher has the extra data
// stripped off, since it can contain private information.
Intent watchIntent = intent.cloneFilter();
abort |= !mService.mController.activityStarting(watchIntent,
aInfo.applicationInfo.packageName);
} catch (RemoteException e) {
mService.mController = null;
}
}
if (abort) {
// 权限检查不通过就退出
if (resultRecord != null) {
resultStack.sendActivityResultLocked(-1, resultRecord, resultWho, requestCode,
Activity.RESULT_CANCELED, null);
}
ActivityOptions.abort(options);
return ActivityManager.START_SUCCESS;
}
// 新建一个ActivityRecord，对应将要启动的Activity
ActivityRecord r = new ActivityRecord(mService, callerApp, callingUid, callingPackage,
intent, resolvedType, aInfo, mService.mConfiguration, resultRecord, resultWho,
requestCode, componentSpecified, voiceSession != null, this, container, options);
if (outActivity != null) {
outActivity[0] = r;
}
if (r.appTimeTracker == null && sourceRecord != null) {
r.appTimeTracker = sourceRecord.appTimeTracker;
}
// 当前的ActivityStack
final ActivityStack stack = mFocusedStack;
if (voiceSession == null && (stack.mResumedActivity == null
|| stack.mResumedActivity.info.applicationInfo.uid != callingUid)) {
if (!mService.checkAppSwitchAllowedLocked(callingPid, callingUid,
realCallingPid, realCallingUid, "Activity start")) {
PendingActivityLaunch pal =
new PendingActivityLaunch(r, sourceRecord, startFlags, stack);
mPendingActivityLaunches.add(pal);
ActivityOptions.abort(options);
return ActivityManager.START_SWITCHES_CANCELED;
}
}
if (mService.mDidAppSwitch) {
mService.mAppSwitchesAllowedTime = 0;
} else {
mService.mDidAppSwitch = true;
}
doPendingActivityLaunchesLocked(false);
err = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, true, options, inTask);
if (err < 0) {
notifyActivityDrawnForKeyguard();
}
return err;
}
- ActivityStackSupervisor.startActivityUncheckedLocked
参数中 r 代表即将要启动的 Activity 对应的 ActivityRecord，sourceRecord 代表调用者。
final int startActivityUncheckedLocked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags,
boolean doResume, Bundle options, TaskRecord inTask) {
final Intent intent = r.intent;
final int callingUid = r.launchedFromUid;
// 如果指定的inTask不在Recents列表中，认为inTask是无效的
// inTask不为空，表示调用者希望在指定的task里面启动activity
// 一般情况下为null
if (inTask != null && !inTask.inRecents) {
inTask = null;
}
// 被启动Activity的启动模式
final boolean launchSingleTop = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TOP;
final boolean launchSingleInstance = r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE;
final boolean launchSingleTask = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK;
int launchFlags = intent.getFlags();
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0 &&
(launchSingleInstance || launchSingleTask)) {
//当Inent中定义的launch flag和manifest中定义的有冲突的话优先使用manifest中定义的
launchFlags &=
~(Intent.FLAG_ACTIVITY_NEW_DOCUMENT | Intent.FLAG_ACTIVITY_MULTIPLE_TASK);
} else {
switch (r.info.documentLaunchMode) {
case ActivityInfo.DOCUMENT_LAUNCH_NONE:
break;
case ActivityInfo.DOCUMENT_LAUNCH_INTO_EXISTING:
launchFlags |= Intent.FLAG_ACTIVITY_NEW_DOCUMENT;
break;
case ActivityInfo.DOCUMENT_LAUNCH_ALWAYS:
launchFlags |= Intent.FLAG_ACTIVITY_NEW_DOCUMENT;
break;
case ActivityInfo.DOCUMENT_LAUNCH_NEVER:
launchFlags &= ~Intent.FLAG_ACTIVITY_MULTIPLE_TASK;
break;
}
}
// 是否为后台启动任务的标志位
final boolean launchTaskBehind = r.mLaunchTaskBehind
&& !launchSingleTask && !launchSingleInstance
&& (launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0;
if (r.resultTo != null && (launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0
&& r.resultTo.task.stack != null) {
// 如果需要返回结果，但是此时的launchFlags有FLAG_ACTIVITY_NEW_TASK，则取消返回结果
r.resultTo.task.stack.sendActivityResultLocked(-1,
r.resultTo, r.resultWho, r.requestCode,
Activity.RESULT_CANCELED, null);
r.resultTo = null;
}
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0 && r.resultTo == null) {
// 赋予FLAG_ACTIVITY_NEW_TASK标志
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
// 如果设置了android:documentLaunchMode为always，那么设置FLAG_ACTIVITY_MULTIPLE_TASK标志
// 即使在其他task里面有该Activity以及启动，仍然新建Task再次启动一个Activity
if (launchTaskBehind
|| r.info.documentLaunchMode == ActivityInfo.DOCUMENT_LAUNCH_ALWAYS) {
launchFlags |= Intent.FLAG_ACTIVITY_MULTIPLE_TASK;
}
}
// 判断一下是否是用户的行为，比如用户按下Home键等等
// 如果是用户的行为的话Activity跳转的时候是要调用onUserLeaveHint()方法的
mUserLeaving = (launchFlags & Intent.FLAG_ACTIVITY_NO_USER_ACTION) == 0;
// 如果设置了不需要resume，那么设置延迟resume标志
if (!doResume) {
r.delayedResume = true;
}
// FLAG_ACTIVITY_PREVIOUS_IS_TOP标志来决定待启动Activity会不会被作为栈顶，
// 如果调用者希望待启动的Activity马上销毁，就会使用该启动参数。
// 通常情况下notTop为null
ActivityRecord notTop =
(launchFlags & Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP) != 0 ? r : null;
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
ActivityRecord checkedCaller = sourceRecord;
if (checkedCaller == null) {
checkedCaller = mFocusedStack.topRunningNonDelayedActivityLocked(notTop);
}
if (!checkedCaller.realActivity.equals(r.realActivity)) {
// 如果调用者和被调用者不是同一个Activity，去掉这个标志，因为这个时候都需要启动
startFlags &= ~ActivityManager.START_FLAG_ONLY_IF_NEEDED;
}
}
boolean addingToTask = false;//表示是否需要在inTask中启动activity
TaskRecord reuseTask = null;//表示可以复用的task
//当调用者不是来自activity，而是明确指定task的情况。
if (sourceRecord == null && inTask != null && inTask.stack != null) {
final Intent baseIntent = inTask.getBaseIntent();
final ActivityRecord root = inTask.getRootActivity();
……
if (root == null) {
// 如果inTask是个空的task，从baseIntent里面挑选出一些flag设置到launchFlags
final int flagsOfInterest = Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_MULTIPLE_TASK | Intent.FLAG_ACTIVITY_NEW_DOCUMENT
| Intent.FLAG_ACTIVITY_RETAIN_IN_RECENTS;
launchFlags = (launchFlags&~flagsOfInterest)
| (baseIntent.getFlags()&flagsOfInterest);
intent.setFlags(launchFlags);
inTask.setIntent(r);
addingToTask = true;
} else if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
// 如果inTask非空，launchFlags要求在新task里面启动那么就不加入到这个task里面去
addingToTask = false;
} else {
// 其他情况就加入到inTask
addingToTask = true;
}
// 如果inTask不为空，就作为复用的task
reuseTask = inTask;
} else {
inTask = null;
}
if (inTask == null) {
// 当没有指定task
if (sourceRecord == null) {
// 调用者不是一个activity，那么就在一个新的task里面启动activity
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) == 0 && inTask == null) {
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
// 如果调用者是一个activity，而且调用者的启动模式是LAUNCH_SINGLE_INSTANCE，
// 那么也需要在新的task里面启动
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
} else if (launchSingleInstance || launchSingleTask) {
// 启动标志位里面是SingleInstance或者launchSingleTask，也需要在新task里面启动
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
}
ActivityInfo newTaskInfo = null;
Intent newTaskIntent = null;
ActivityStack sourceStack;
if (sourceRecord != null) {
if (sourceRecord.finishing) {
// 如果调用者activity处于正在销毁的状态，那么就需要在新的task里启动
// 并且保存一些调用者的信息，并把sourceRecord和sourceStack置空
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
newTaskInfo = sourceRecord.info;
newTaskIntent = sourceRecord.task.intent;
}
sourceRecord = null;
sourceStack = null;
} else {
// 如果不在销毁状态，把其所在的栈赋于sourceStack
sourceStack = sourceRecord.task.stack;
}
} else {
sourceStack = null;
}
boolean movedHome = false;
ActivityStack targetStack;
// 至此，启动参数的修正工作结束，设置给intent
intent.setFlags(launchFlags);
// 看是否需要动画
final boolean noAnimation = (launchFlags & Intent.FLAG_ACTIVITY_NO_ANIMATION) != 0;
// FLAG_ACTIVITY_NEW_TASK && FLAG_ACTIVITY_MULTIPLE_TASK 表示不是在当前任务中启动，
// 但是要查看是否有目标Activity已经存在的任务，同launchSingleInstance和launchSingleTask
if (((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags & Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| launchSingleInstance || launchSingleTask) {
if (inTask == null && r.resultTo == null) {
// 在没有指定task且不要返回结果的情况下，去查找是否有匹配的activity
// findTaskLocked是找到匹配的目标ActivityRecord所在的任务栈(TaskRecord)，包含taskAffinity的操作
// 这个方法后面会详细介绍
// 从栈顶至栈底遍历ActivityStack中的所有Activity，根据Intent和ActivityInfo这
// 两个参数得到的Activity的包名
ActivityRecord intentActivity = !launchSingleInstance ?
findTaskLocked(r) : findActivityLocked(intent, r.info);
if (intentActivity != null) {
// intentActivity不为空表示找到目标activity，那么目标Activity所在的任务(TaskRecord)
// 和任务所在的栈(ActivityRecord)就是宿主任务和宿主栈
// 这里通过isLockTaskModeViolation锁定屏幕的那些Task
if (isLockTaskModeViolation(intentActivity.task,
(launchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))) {
// 如果不是锁定的task，就结束启动流程
// lock task mode 是Android 5.0 Lollipop添加的功能
showLockTaskToast();
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
if (r.task == null) {
r.task = intentActivity.task;
}
if (intentActivity.task.intent == null) {
intentActivity.task.setIntent(r);
}
targetStack = intentActivity.task.stack;
targetStack.mLastPausedActivity = null;
// 如果目标task不在前台就需要把它移至前台
// 这里首先获取焦点所在的栈
final ActivityStack focusStack = getFocusedStack();
//从焦点栈里面找到当前可见的ActivityRecord
ActivityRecord curTop = (focusStack == null)
? null : focusStack.topRunningNonDelayedActivityLocked(notTop);
boolean movedToFront = false;
if (curTop != null && (curTop.task != intentActivity.task ||
curTop.task != focusStack.topTask())) {
// 满足上面的条件表示待启动的activity和当前可见activity不在同一个task
// 那么就需要将待启动的activity所在的栈移动到前台
r.intent.addFlags(Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT);
if (sourceRecord == null || (sourceStack.topActivity() != null &&
sourceStack.topActivity().task == sourceRecord.task)) {
if (launchTaskBehind && sourceRecord != null) {
intentActivity.setTaskToAffiliateWith(sourceRecord.task);
}
movedHome = true;
// 将目标任务移动到栈顶
targetStack.moveTaskToFrontLocked(intentActivity.task, noAnimation,
options, r.appTimeTracker, "bringingFoundTaskToFront");
movedToFront = true;
if ((launchFlags &
(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME)) {
//将toReturnTo设置为home
intentActivity.task.setTaskToReturnTo(HOME_ACTIVITY_TYPE);
}
options = null;
}
}
if (!movedToFront) {
// 将当前栈移动到前台
targetStack.moveToFront("intentActivityFound");
}
// 根据需要重置activity所在的task
if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
intentActivity = targetStack.resetTaskIfNeededLocked(intentActivity, r);
}
if ((startFlags & ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
// 如果不需要启动一个新的activity，结束启动流程
if (doResume) {
resumeTopActivitiesLocked(targetStack, null, options);
// 如果没有移动到前台，通知Keyguard
if (!movedToFront) {
notifyActivityDrawnForKeyguard();
}
} else {
ActivityOptions.abort(options);
}
return ActivityManager.START_RETURN_INTENT_TO_CALLER;
}
if ((launchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK)) {
// 这里需要移除目标task中所有关联的其他activity，即要完全替代目标task
// 将该启动activity变为task中的根activity
reuseTask = intentActivity.task;
reuseTask.performClearTaskLocked();
reuseTask.setIntent(r);
} else if ((launchFlags & FLAG_ACTIVITY_CLEAR_TOP) != 0
|| launchSingleInstance || launchSingleTask) {
// 清除task中目标activity上面的所有activity，返回目标activity
ActivityRecord top =
intentActivity.task.performClearTaskLocked(r, launchFlags);
if (top != null) {
if (top.frontOfTask) {
top.task.setIntent(r);
}
//触发调用onNewIntent()
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
} else {
// A special case: we need to start the activity because it is not
// currently running, and the caller has asked to clear the current
// task to have this activity at the top.
addingToTask = true;
// Now pretend like this activity is being started by the top of its
// task, so it is put in the right place.
sourceRecord = intentActivity;
TaskRecord task = sourceRecord.task;
if (task != null && task.stack == null) {
// Target stack got cleared when we all activities were removed
// above. Go ahead and reset it.
targetStack = computeStackFocus(sourceRecord, false /* newTask */);
targetStack.addTask(
task, !launchTaskBehind /* toTop */, false /* moving */);
}
}
} else if (r.realActivity.equals(intentActivity.task.realActivity)) {
// In this case the top activity on the task is the
// same as the one being launched, so we take that
// as a request to bring the task to the foreground.
// If the top activity in the task is the root
// activity, deliver this new intent to it if it
// desires.
if (((launchFlags&Intent.FLAG_ACTIVITY_SINGLE_TOP) != 0 || launchSingleTop)
&& intentActivity.realActivity.equals(r.realActivity)) {
ActivityStack.logStartActivity(EventLogTags.AM_NEW_INTENT, r,
intentActivity.task);
if (intentActivity.frontOfTask) {
intentActivity.task.setIntent(r);
}
intentActivity.deliverNewIntentLocked(callingUid, r.intent,
r.launchedFromPackage);
} else if (!r.intent.filterEquals(intentActivity.task.intent)) {
// In this case we are launching the root activity
// of the task, but with a different intent. We
// should start a new instance on top.
addingToTask = true;
sourceRecord = intentActivity;
}
} else if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) == 0) {
// In this case an activity is being launched in to an
// existing task, without resetting that task. This
// is typically the situation of launching an activity
// from a notification or shortcut. We want to place
// the new activity on top of the current task.
addingToTask = true;
sourceRecord = intentActivity;
} else if (!intentActivity.task.rootWasReset) {
// In this case we are launching in to an existing task
// that has not yet been started from its front door.
// The current task has been brought to the front.
// Ideally, we'd probably like to place this new task
// at the bottom of its stack, but that's a little hard
// to do with the current organization of the code so
// for now we'll just drop it.
intentActivity.task.setIntent(r);
}
if (!addingToTask && reuseTask == null) {
// 如果不需要加入指定的task，且不用复用task，那么直接把找到的目标activity推到前台
// 并结束启动流程
if (doResume) {
targetStack.resumeTopActivityLocked(null, options);
if (!movedToFront) {
notifyActivityDrawnForKeyguard();
}
} else {
ActivityOptions.abort(options);
}
return ActivityManager.START_TASK_TO_FRONT;
}
}//end of (intentActivity != null)
}//end of (inTask == null && r.resultTo == null)
}
if (r.packageName != null) {
// 待启动activity包名不为空
ActivityStack topStack = mFocusedStack;
ActivityRecord top = topStack.topRunningNonDelayedActivityLocked(notTop);
if (top != null && r.resultTo == null) {
if (top.realActivity.equals(r.realActivity) && top.userId == r.userId) {
// 待启动的activity和前台显示的activity是同一个activity的情况
if (top.app != null && top.app.thread != null) {
if ((launchFlags & Intent.FLAG_ACTIVITY_SINGLE_TOP) != 0
|| launchSingleTop || launchSingleTask) {
ActivityStack.logStartActivity(EventLogTags.AM_NEW_INTENT, top,
top.task);
topStack.mLastPausedActivity = null;
if (doResume) {
resumeTopActivitiesLocked();
}
ActivityOptions.abort(options);
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
return ActivityManager.START_RETURN_INTENT_TO_CALLER;
}
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
return ActivityManager.START_DELIVERED_TO_TOP;
}
}
}
}
} else {
//如果目标activity包名为空，表示找不到待启动的activity，结束启动流程
if (r.resultTo != null && r.resultTo.task.stack != null) {
r.resultTo.task.stack.sendActivityResultLocked(-1, r.resultTo, r.resultWho,
r.requestCode, Activity.RESULT_CANCELED, null);
}
ActivityOptions.abort(options);
return ActivityManager.START_CLASS_NOT_FOUND;
}
目标activity不存在的情况：
// 接下来处理目标activity不存在的情况
boolean newTask = false;
boolean keepCurTransition = false;
TaskRecord taskToAffiliate = launchTaskBehind && sourceRecord != null ?
sourceRecord.task : null;
if (r.resultTo == null && inTask == null && !addingToTask
&& (launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
// 这种情况下要在一个新的task中启动activity
newTask = true;
targetStack = computeStackFocus(r, newTask);
targetStack.moveToFront("startingNewTask");
if (reuseTask == null) {
// 如果没有可以复用的就新建一个
r.setTask(targetStack.createTaskRecord(getNextTaskId(),
newTaskInfo != null ? newTaskInfo : r.info,
newTaskIntent != null ? newTaskIntent : intent,
voiceSession, voiceInteractor, !launchTaskBehind /* toTop */),
taskToAffiliate);
} else {
// 复用task
r.setTask(reuseTask, taskToAffiliate);
}
if (isLockTaskModeViolation(r.task)) {
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
if (!movedHome) {
if ((launchFlags &
(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME)) {
// 把当前新启动的任务置于Home任务之上，也就是按back键从这个任务返回的时候
// 会回到home，即使这个不是他们最后看见的activity
r.task.setTaskToReturnTo(HOME_ACTIVITY_TYPE);
}
}
} else if (sourceRecord != null) {
// 不用在新task中启动activity
final TaskRecord sourceTask = sourceRecord.task;
if (isLockTaskModeViolation(sourceTask)) {
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
// 那么目标activity的栈也就是调用者所在的栈
targetStack = sourceTask.stack;
targetStack.moveToFront("sourceStackToFront");
final TaskRecord topTask = targetStack.topTask();
if (topTask != sourceTask) {
// 移动task到前台
targetStack.moveTaskToFrontLocked(sourceTask, noAnimation, options,
r.appTimeTracker, "sourceTaskToFront");
}
if (!addingToTask && (launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {
// 清除activity
ActivityRecord top = sourceTask.performClearTaskLocked(r, launchFlags);
keepCurTransition = true;
if (top != null) {
ActivityStack.logStartActivity(EventLogTags.AM_NEW_INTENT, r, top.task);
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
targetStack.mLastPausedActivity = null;
if (doResume) {
targetStack.resumeTopActivityLocked(null);
}
ActivityOptions.abort(options);
return ActivityManager.START_DELIVERED_TO_TOP;
}
} else if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_REORDER_TO_FRONT) != 0) {
final ActivityRecord top = sourceTask.findActivityInHistoryLocked(r);
if (top != null) {
final TaskRecord task = top.task;
task.moveActivityToFrontLocked(top);
ActivityStack.logStartActivity(EventLogTags.AM_NEW_INTENT, r, task);
top.updateOptionsLocked(options);
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
targetStack.mLastPausedActivity = null;
if (doResume) {
targetStack.resumeTopActivityLocked(null);
}
return ActivityManager.START_DELIVERED_TO_TOP;
}
}
r.setTask(sourceTask, null);
} else if (inTask != null) {
// 在指定的task中启动activity
if (isLockTaskModeViolation(inTask)) {
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
targetStack = inTask.stack;
targetStack.moveTaskToFrontLocked(inTask, noAnimation, options, r.appTimeTracker,
"inTaskToFront");
// check一下是在这个task中启动一个新的activity或者是复用当前栈顶的activity
ActivityRecord top = inTask.getTopActivity();
if (top != null && top.realActivity.equals(r.realActivity) && top.userId == r.userId) {
if ((launchFlags & Intent.FLAG_ACTIVITY_SINGLE_TOP) != 0
|| launchSingleTop || launchSingleTask) {
ActivityStack.logStartActivity(EventLogTags.AM_NEW_INTENT, top, top.task);
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
return ActivityManager.START_RETURN_INTENT_TO_CALLER;
}
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
return ActivityManager.START_DELIVERED_TO_TOP;
}
}
if (!addingToTask) {
ActivityOptions.abort(options);
return ActivityManager.START_TASK_TO_FRONT;
}
r.setTask(inTask, null);
} else {
// 既不启动一个新的activity，也不在指定的task中启动
// 目前不会走到这个分支中
targetStack = computeStackFocus(r, newTask);
targetStack.moveToFront("addingToTopTask");
ActivityRecord prev = targetStack.topActivity();
r.setTask(prev != null ? prev.task : targetStack.createTaskRecord(getNextTaskId(),
r.info, intent, null, null, true), null);
mWindowManager.moveTaskToTop(r.task.taskId);
}
mService.grantUriPermissionFromIntentLocked(callingUid, r.packageName,
intent, r.getUriPermissionsLocked(), r.userId);
if (sourceRecord != null && sourceRecord.isRecentsActivity()) {
r.task.setTaskToReturnTo(RECENTS_ACTIVITY_TYPE);
}
if (newTask) {
EventLog.writeEvent(EventLogTags.AM_CREATE_TASK, r.userId, r.task.taskId);
}
ActivityStack.logStartActivity(EventLogTags.AM_CREATE_ACTIVITY, r, r.task);
targetStack.mLastPausedActivity = null;
// 进行下一步流程，启动activity
targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);
if (!launchTaskBehind) {
// 如果不是在后台启动就把焦点设置在当前activity
mService.setFocusedActivityLocked(r, "startedActivity");
}
return ActivityManager.START_SUCCESS;
}
可以看到这个方法首先是修正了一些启动参数，接着根据目标Activity是否存在分别进行了处理，然后启动activity。
- ActivityStack.startActivityLocked ：判断是否需要创建一个新的任务来启动Activity。
final void startActivityLocked(ActivityRecord r, boolean newTask,
boolean doResume, boolean keepCurTransition, Bundle options) {
TaskRecord rTask = r.task;
final int taskId = rTask.taskId;
if (!r.mLaunchTaskBehind && (taskForIdLocked(taskId) == null || newTask)) {
// 历史activity被清除了或者是明确要求在新的task启动activity
// 将task插入stack栈顶
insertTaskAtTop(rTask, r);
// 调用WindowManagerService
mWindowManager.moveTaskToTop(taskId);
}
TaskRecord task = null;
if (!newTask) {
// 在一个已经存在的task中启动activity
boolean startIt = true;// 是否需要启动activity的标志位
for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
task = mTaskHistory.get(taskNdx);
if (task.getTopActivity() == null) {
// 该task中已经没有activity了
continue;
}
if (task == r.task) {
// 匹配到目标task
if (!startIt) {
// 如果不需要启动，就先添加到栈顶
task.addActivityToTop(r);
r.putInHistory();
// 调用WindowManagerService 添加apptoken
mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken,
r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen,
(r.info.flags & ActivityInfo.FLAG_SHOW_FOR_ALL_USERS) != 0,
r.userId, r.info.configChanges, task.voiceSession != null,
r.mLaunchTaskBehind);
if (VALIDATE_TOKENS) {
validateAppTokensLocked();
}
ActivityOptions.abort(options);
return;
}
break;
} else if (task.numFullscreen > 0) {
// 如果在这个任务中有全屏显示的activity，就先不显示
startIt = false;
}
}
}
// 走到这里已经把目标activity所在的task推到了stack的栈顶
// 如果不需要在新的activity中启动，而且上面查到了目标task，且task在栈顶，就不需要调用onUserLeaving方法
if (task == r.task && mTaskHistory.indexOf(task) != (mTaskHistory.size() - 1)) {
mStackSupervisor.mUserLeaving = false;
}
task = r.task;
// 将activity放到task的栈顶
task.addActivityToTop(r);
// activity移动或者销毁之后调用setFrontOfTask方法
task.setFrontOfTask();
r.putInHistory();
if (!isHomeStack() || numActivities() > 0) {
// 进入这个分支的条件当前stack不是桌面stack，也即当前是否是桌面。或者当前stack中已有task
// 一些切换动画相关的操作
boolean showStartingIcon = newTask;
ProcessRecord proc = r.app;
if (proc == null) {
proc = mService.mProcessNames.get(r.processName, r.info.applicationInfo.uid);
}
if (proc == null || proc.thread == null) {
showStartingIcon = true;
}
if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_NO_ANIMATION) != 0) {
mWindowManager.prepareAppTransition(AppTransition.TRANSIT_NONE, keepCurTransition);
mNoAnimActivities.add(r);
} else {
mWindowManager.prepareAppTransition(newTask
? r.mLaunchTaskBehind
? AppTransition.TRANSIT_TASK_OPEN_BEHIND
: AppTransition.TRANSIT_TASK_OPEN
: AppTransition.TRANSIT_ACTIVITY_OPEN, keepCurTransition);
mNoAnimActivities.remove(r);
}
// 调用WindowManagerService 添加apptoken
mWindowManager.addAppToken(task.mActivities.indexOf(r),
r.appToken, r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen,
(r.info.flags & ActivityInfo.FLAG_SHOW_FOR_ALL_USERS) != 0, r.userId,
r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind);
boolean doShow = true;
// 一些显示StartingWindow的操作
if (newTask) {
if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
resetTaskIfNeededLocked(r, r);
doShow = topRunningNonDelayedActivityLocked(null) == r;
}
} else if (options != null && new ActivityOptions(options).getAnimationType()
== ActivityOptions.ANIM_SCENE_TRANSITION) {
doShow = false;
}
if (r.mLaunchTaskBehind) {
mWindowManager.setAppVisibility(r.appToken, true);
ensureActivitiesVisibleLocked(null, 0);
} else if (SHOW_APP_STARTING_PREVIEW && doShow) {
ActivityRecord prev = mResumedActivity;
// prev 表示当前在resumed状态的activity
if (prev != null) {
// 如果它和目标activity不在同一个task
if (prev.task != r.task) {
prev = null;
}
// 在同一个task且已经显示
else if (prev.nowVisible) {
prev = null;
}
}
mWindowManager.setAppStartingWindow(
r.appToken, r.packageName, r.theme,
mService.compatibilityInfoForPackageLocked(
r.info.applicationInfo), r.nonLocalizedLabel,
r.labelRes, r.icon, r.logo, r.windowFlags,
prev != null ? prev.appToken : null, showStartingIcon);
r.mStartingWindowShown = true;
}
} else {
// 进入这个分支条件：目标stack中还没有任何activity，那就不要做任何动画
// 调用addAppToken绑定窗口
mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken,
r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen,
(r.info.flags & ActivityInfo.FLAG_SHOW_FOR_ALL_USERS) != 0, r.userId,
r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind);
ActivityOptions.abort(options);
options = null;
}
if (VALIDATE_TOKENS) {
validateAppTokensLocked();
}
// 显示activity
if (doResume) {
mStackSupervisor.resumeTopActivitiesLocked(this, r, options);
}
}
- ActivityStack.resumeTopActivityLocked ：获取栈顶的activity，并通知Launcher应该pause掉这个Activity以便启动新的activity。
final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) {
if (mStackSupervisor.inResumeTopActivity) {
// Don't even start recursing.
return false;
}
boolean result = false;
try {
// 防止递归调用
mStackSupervisor.inResumeTopActivity = true;
if (mService.mLockScreenShown == ActivityManagerService.LOCK_SCREEN_LEAVING) {
mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN;
mService.updateSleepIfNeededLocked();
}
result = resumeTopActivityInnerLocked(prev, options);
} finally {
mStackSupervisor.inResumeTopActivity = false;
}
return result;
}
- ActivityStack.startPausingLocked
final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping,
ActivityRecord resuming, boolean pauseImmediately) {
if (mPausingActivity != null) {
Slog.wtf(TAG, "Going to pause when pause is already pending for " + mPausingActivity
+ " state=" + mPausingActivity.getState());
if (!shouldSleepActivities()) {
// Avoid recursion among check for sleep and complete pause during sleeping.
// Because activity will be paused immediately after resume, just let pause
// be completed by the order of activity paused from clients.
completePauseLocked(false, resuming);
}
}
ActivityRecord prev = mResumedActivity;
if (prev == null) {
if (resuming == null) {
Slog.wtf(TAG, "Trying to pause when nothing is resumed");
mStackSupervisor.resumeFocusedStackTopActivityLocked();
}
return false;
}
if (prev == resuming) {
Slog.wtf(TAG, "Trying to pause activity that is in process of being resumed");
return false;
}
if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to PAUSING: " + prev);
else if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Start pausing: " + prev);
mPausingActivity = prev;
mLastPausedActivity = prev;
mLastNoHistoryActivity = (prev.intent.getFlags() & Intent.FLAG_ACTIVITY_NO_HISTORY) != 0
|| (prev.info.flags & ActivityInfo.FLAG_NO_HISTORY) != 0 ? prev : null;
prev.setState(PAUSING, "startPausingLocked");
prev.getTask().touchActiveTime();
clearLaunchTime(prev);
mStackSupervisor.getLaunchTimeTracker().stopFullyDrawnTraceIfNeeded(getWindowingMode());
mService.updateCpuStats();
if (prev.app != null && prev.app.thread != null) {
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Enqueueing pending pause: " + prev);
try {
EventLogTags.writeAmPauseActivity(prev.userId, System.identityHashCode(prev),
prev.shortComponentName, "userLeaving=" + userLeaving);
mService.updateUsageStats(prev, false);
mService.getLifecycleManager().scheduleTransaction(prev.app.thread, prev.appToken,
PauseActivityItem.obtain(prev.finishing, userLeaving,
prev.configChangeFlags, pauseImmediately));
} catch (Exception e) {
// Ignore exception, if process died other code will cleanup.
Slog.w(TAG, "Exception thrown during pause", e);
mPausingActivity = null;
mLastPausedActivity = null;
mLastNoHistoryActivity = null;
}
} else {
mPausingActivity = null;
mLastPausedActivity = null;
mLastNoHistoryActivity = null;
}
// If we are not going to sleep, we want to ensure the device is
// awake until the next activity is started.
if (!uiSleeping && !mService.isSleepingOrShuttingDownLocked()) {
mStackSupervisor.acquireLaunchWakelock();
}
if (mPausingActivity != null) {
// Have the window manager pause its key dispatching until the new
// activity has started. If we're pausing the activity just because
// the screen is being turned off and the UI is sleeping, don't interrupt
// key dispatch; the same activity will pick it up again on wakeup.
if (!uiSleeping) {
prev.pauseKeyDispatchingLocked();
} else if (DEBUG_PAUSE) {
Slog.v(TAG_PAUSE, "Key dispatch not paused for screen off");
}
if (pauseImmediately) {
// If the caller said they don't want to wait for the pause, then complete
// the pause now.
completePauseLocked(false, resuming);
return false;
} else {
schedulePauseTimeout(prev);
return true;
}
} else {
// This activity failed to schedule the
// pause, so just treat it as being paused now.
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Activity not running, resuming next.");
if (resuming == null) {
mStackSupervisor.resumeFocusedStackTopActivityLocked();
}
return false;
}
}
- ApplicationThreadProxy.schedulePauseActivity
第三阶段： pause Launcher的Activity，并通知AMS已经paused（在Launcher所在进程执行）
- ApplicationThread.schedulePauseActivity
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport) {
int seq = getLifecycleSeq();
if (DEBUG_ORDER) Slog.d(TAG, "pauseActivity " + ActivityThread.this
+ " operation received seq: " + seq);
sendMessage(
finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
token,
(userLeaving ? USER_LEAVING : 0) | (dontReport ? DONT_REPORT : 0),
configChanges,
seq);
}
- ActivityThread.queueOrSendMessage
- H.handleMessage
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case EXIT_APPLICATION:
if (mInitialApplication != null) {
mInitialApplication.onTerminate();
}
Looper.myLooper().quit();
break;
case RECEIVER:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveComp");
handleReceiver((ReceiverData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case CREATE_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceCreate: " + String.valueOf(msg.obj)));
handleCreateService((CreateServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case UNBIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceUnbind");
handleUnbindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SERVICE_ARGS:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceStart: " + String.valueOf(msg.obj)));
handleServiceArgs((ServiceArgsData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case STOP_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStop");
handleStopService((IBinder)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case CONFIGURATION_CHANGED:
handleConfigurationChanged((Configuration) msg.obj);
break;
case CLEAN_UP_CONTEXT:
ContextCleanupInfo cci = (ContextCleanupInfo)msg.obj;
cci.context.performFinalCleanup(cci.who, cci.what);
break;
case GC_WHEN_IDLE:
scheduleGcIdler();
break;
case DUMP_SERVICE:
handleDumpService((DumpComponentInfo)msg.obj);
break;
case LOW_MEMORY:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "lowMemory");
handleLowMemory();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case PROFILER_CONTROL:
handleProfilerControl(msg.arg1 != 0, (ProfilerInfo)msg.obj, msg.arg2);
break;
case CREATE_BACKUP_AGENT:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "backupCreateAgent");
handleCreateBackupAgent((CreateBackupAgentData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case DESTROY_BACKUP_AGENT:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "backupDestroyAgent");
handleDestroyBackupAgent((CreateBackupAgentData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SUICIDE:
Process.killProcess(Process.myPid());
break;
case REMOVE_PROVIDER:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "providerRemove");
completeRemoveProvider((ProviderRefCount)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case ENABLE_JIT:
ensureJitEnabled();
break;
case DISPATCH_PACKAGE_BROADCAST:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastPackage");
handleDispatchPackageBroadcast(msg.arg1, (String[])msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SCHEDULE_CRASH:
throw new RemoteServiceException((String)msg.obj);
case DUMP_HEAP:
handleDumpHeap((DumpHeapData) msg.obj);
break;
case DUMP_ACTIVITY:
handleDumpActivity((DumpComponentInfo)msg.obj);
break;
case DUMP_PROVIDER:
handleDumpProvider((DumpComponentInfo)msg.obj);
break;
case SLEEPING:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "sleeping");
handleSleeping((IBinder)msg.obj, msg.arg1 != 0);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SET_CORE_SETTINGS:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "setCoreSettings");
handleSetCoreSettings((Bundle) msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case UPDATE_PACKAGE_COMPATIBILITY_INFO:
handleUpdatePackageCompatibilityInfo((UpdateCompatibilityData)msg.obj);
break;
case UNSTABLE_PROVIDER_DIED:
handleUnstableProviderDied((IBinder)msg.obj, false);
break;
case REQUEST_ASSIST_CONTEXT_EXTRAS:
handleRequestAssistContextExtras((RequestAssistContextExtras)msg.obj);
break;
case TRANSLUCENT_CONVERSION_COMPLETE:
handleTranslucentConversionComplete((IBinder)msg.obj, msg.arg1 == 1);
break;
case INSTALL_PROVIDER:
handleInstallProvider((ProviderInfo) msg.obj);
break;
case ON_NEW_ACTIVITY_OPTIONS:
Pair<IBinder, ActivityOptions> pair = (Pair<IBinder, ActivityOptions>) msg.obj;
onNewActivityOptions(pair.first, pair.second);
break;
case ENTER_ANIMATION_COMPLETE:
handleEnterAnimationComplete((IBinder) msg.obj);
break;
case START_BINDER_TRACKING:
handleStartBinderTracking();
break;
case STOP_BINDER_TRACKING_AND_DUMP:
handleStopBinderTrackingAndDump((ParcelFileDescriptor) msg.obj);
break;
case LOCAL_VOICE_INTERACTION_STARTED:
handleLocalVoiceInteractionStarted((IBinder) ((SomeArgs) msg.obj).arg1,
(IVoiceInteractor) ((SomeArgs) msg.obj).arg2);
break;
case ATTACH_AGENT: {
Application app = getApplication();
handleAttachAgent((String) msg.obj, app != null ? app.mLoadedApk : null);
break;
}
case APPLICATION_INFO_CHANGED:
mUpdatingSystemConfig = true;
try {
handleApplicationInfoChanged((ApplicationInfo) msg.obj);
} finally {
mUpdatingSystemConfig = false;
}
break;
case RUN_ISOLATED_ENTRY_POINT:
handleRunIsolatedEntryPoint((String) ((SomeArgs) msg.obj).arg1,
(String[]) ((SomeArgs) msg.obj).arg2);
break;
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
if (isSystem()) {
// Client transactions inside system process are recycled on the client side
// instead of ClientLifecycleManager to avoid being cleared before this
// message is handled.
transaction.recycle();
}
// TODO(lifecycler): Recycle locally scheduled transactions.
break;
case RELAUNCH_ACTIVITY:
handleRelaunchActivityLocally((IBinder) msg.obj);
break;
}
Object obj = msg.obj;
if (obj instanceof SomeArgs) {
((SomeArgs) obj).recycle();
}
if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what));
}
- ActivityThread.handlePauseActivity
public void handlePauseActivity(IBinder token, boolean finished, boolean userLeaving,
int configChanges, PendingTransactionActions pendingActions, String reason) {
ActivityClientRecord r = mActivities.get(token);
if (r != null) {
if (userLeaving) {
performUserLeavingActivity(r);
}
r.activity.mConfigChangeFlags |= configChanges;
performPauseActivity(r, finished, reason, pendingActions);
// Make sure any pending writes are now committed.
if (r.isPreHoneycomb()) {
QueuedWork.waitToFinish();
}
mSomeActivitiesChanged = true;
}
}
- ActivityManagerProxy.activityPaused
第四阶段：检查activity所在进程是否存在，如果存在，就直接通知这个进程，在该进程中启动Activity；不存在的话，会调用Process.start创建一个新进程（执行在AMS进程）
- ActivityManagerService.activityPaused
@Override
public final void activityPaused(IBinder token) {
final long origId = Binder.clearCallingIdentity();
synchronized(this) {
ActivityStack stack = ActivityRecord.getStackLocked(token);
if (stack != null) {
stack.activityPausedLocked(token, false);
}
}
Binder.restoreCallingIdentity(origId);
}
- ActivityStack.activityPaused
- ActivityStack.completePauseLocked
private void completePauseLocked(boolean resumeNext, ActivityRecord resuming) {
ActivityRecord prev = mPausingActivity;
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Complete pause: " + prev);
if (prev != null) {
final boolean wasStopping = prev.state == STOPPING;
prev.state = ActivityState.PAUSED;
if (prev.finishing) {
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Executing finish of activity: " + prev);
prev = finishCurrentActivityLocked(prev, FINISH_AFTER_VISIBLE, false);
} else if (prev.app != null) {
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Enqueue pending stop if needed: " + prev
+ " wasStopping=" + wasStopping + " visible=" + prev.visible);
if (mStackSupervisor.mActivitiesWaitingForVisibleActivity.remove(prev)) {
if (DEBUG_SWITCH || DEBUG_PAUSE) Slog.v(TAG_PAUSE,
"Complete pause, no longer waiting: " + prev);
}
if (prev.deferRelaunchUntilPaused) {
// Complete the deferred relaunch that was waiting for pause to complete.
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Re-launching after pause: " + prev);
prev.relaunchActivityLocked(false /* andResume */,
prev.preserveWindowOnDeferredRelaunch);
} else if (wasStopping) {
// We are also stopping, the stop request must have gone soon after the pause.
// We can't clobber it, because the stop confirmation will not be handled.
// We don't need to schedule another stop, we only need to let it happen.
prev.state = STOPPING;
} else if ((!prev.visible && !hasVisibleBehindActivity())
|| mService.isSleepingOrShuttingDownLocked()) {
// Clear out any deferred client hide we might currently have.
prev.setDeferHidingClient(false);
// If we were visible then resumeTopActivities will release resources before
// stopping.
addToStopping(prev, true /* scheduleIdle */, false /* idleDelayed */);
}
} else {
if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "App died during pause, not stopping: " + prev);
prev = null;
}
// It is possible the activity was freezing the screen before it was paused.
// In that case go ahead and remove the freeze this activity has on the screen
// since it is no longer visible.
if (prev != null) {
prev.stopFreezingScreenLocked(true /*force*/);
}
mPausingActivity = null;
}
if (resumeNext) {
final ActivityStack topStack = mStackSupervisor.getFocusedStack();
if (!mService.isSleepingOrShuttingDownLocked()) {
mStackSupervisor.resumeFocusedStackTopActivityLocked(topStack, prev, null);
} else {
mStackSupervisor.checkReadyForSleepLocked();
ActivityRecord top = topStack.topRunningActivityLocked();
if (top == null || (prev != null && top != prev)) {
// If there are no more activities available to run, do resume anyway to start
// something. Also if the top activity on the stack is not the just paused
// activity, we need to go ahead and resume it to ensure we complete an
// in-flight app switch.
mStackSupervisor.resumeFocusedStackTopActivityLocked();
}
}
}
if (prev != null) {
prev.resumeKeyDispatchingLocked();
if (prev.app != null && prev.cpuTimeAtResume > 0
&& mService.mBatteryStatsService.isOnBattery()) {
long diff = mService.mProcessCpuTracker.getCpuTimeForPid(prev.app.pid)
- prev.cpuTimeAtResume;
if (diff > 0) {
BatteryStatsImpl bsi = mService.mBatteryStatsService.getActiveStatistics();
synchronized (bsi) {
BatteryStatsImpl.Uid.Proc ps =
bsi.getProcessStatsLocked(prev.info.applicationInfo.uid,
prev.info.packageName);
if (ps != null) {
ps.addForegroundTimeLocked(diff);
}
}
}
}
prev.cpuTimeAtResume = 0; // reset it
}
// Notify when the task stack has changed, but only if visibilities changed (not just
// focus). Also if there is an active pinned stack - we always want to notify it about
// task stack changes, because its positioning may depend on it.
if (mStackSupervisor.mAppVisibilitiesChangedSinceLastPause
|| mService.mStackSupervisor.getStack(PINNED_STACK_ID) != null) {
mService.mTaskChangeNotificationController.notifyTaskStackChanged();
mStackSupervisor.mAppVisibilitiesChangedSinceLastPause = false;
}
mStackSupervisor.ensureActivitiesVisibleLocked(resuming, 0, !PRESERVE_WINDOWS);
}
- ActivityStack.resumeTopActivityLocked
- ActivityStack.startSpecificActivityLocked
- ActivityManagerService.startProcessLocked
@GuardedBy("this")
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
return startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingType,
hostingName, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
null /* crashHandler */);
}
@GuardedBy("this")
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
long startTime = SystemClock.elapsedRealtime();
ProcessRecord app;
if (!isolated) {
app = getProcessRecordLocked(processName, info.uid, keepIfLarge);
checkTime(startTime, "startProcess: after getProcessRecord");
if ((intentFlags & Intent.FLAG_FROM_BACKGROUND) != 0) {
// If we are in the background, then check to see if this process
// is bad. If so, we will just silently fail.
if (mAppErrors.isBadProcessLocked(info)) {
if (DEBUG_PROCESSES) Slog.v(TAG, "Bad process: " + info.uid
+ "/" + info.processName);
return null;
}
} else {
// When the user is explicitly starting a process, then clear its
// crash count so that we won't make it bad until they see at
// least one crash dialog again, and make the process good again
// if it had been bad.
if (DEBUG_PROCESSES) Slog.v(TAG, "Clearing bad process: " + info.uid
+ "/" + info.processName);
mAppErrors.resetProcessCrashTimeLocked(info);
if (mAppErrors.isBadProcessLocked(info)) {
EventLog.writeEvent(EventLogTags.AM_PROC_GOOD,
UserHandle.getUserId(info.uid), info.uid,
info.processName);
mAppErrors.clearBadProcessLocked(info);
if (app != null) {
app.bad = false;
}
}
}
} else {
// If this is an isolated process, it can't re-use an existing process.
app = null;
}
// We don't have to do anything more if:
// (1) There is an existing application record; and
// (2) The caller doesn't think it is dead, OR there is no thread
// object attached to it so we know it couldn't have crashed; and
// (3) There is a pid assigned to it, so it is either starting or
// already running.
if (DEBUG_PROCESSES) Slog.v(TAG_PROCESSES, "startProcess: name=" + processName
+ " app=" + app + " knownToBeDead=" + knownToBeDead
+ " thread=" + (app != null ? app.thread : null)
+ " pid=" + (app != null ? app.pid : -1));
if (app != null && app.pid > 0) {
if ((!knownToBeDead && !app.killed) || app.thread == null) {
// We already have the app running, or are waiting for it to
// come up (we have a pid but not yet its thread), so keep it.
if (DEBUG_PROCESSES) Slog.v(TAG_PROCESSES, "App already running: " + app);
// If this is a new package in the process, add the package to the list
app.addPackage(info.packageName, info.versionCode, mProcessStats);
checkTime(startTime, "startProcess: done, added package to proc");
return app;
}
// An application record is attached to a previous process,
// clean it up now.
if (DEBUG_PROCESSES || DEBUG_CLEANUP) Slog.v(TAG_PROCESSES, "App died: " + app);
checkTime(startTime, "startProcess: bad proc running, killing");
killProcessGroup(app.uid, app.pid);
handleAppDiedLocked(app, true, true);
checkTime(startTime, "startProcess: done killing old proc");
}
String hostingNameStr = hostingName != null
? hostingName.flattenToShortString() : null;
if (app == null) {
checkTime(startTime, "startProcess: creating new process record");
app = newProcessRecordLocked(info, processName, isolated, isolatedUid);
if (app == null) {
Slog.w(TAG, "Failed making new process record for "
+ processName + "/" + info.uid + " isolated=" + isolated);
return null;
}
app.crashHandler = crashHandler;
app.isolatedEntryPoint = entryPoint;
app.isolatedEntryPointArgs = entryPointArgs;
checkTime(startTime, "startProcess: done creating new process record");
} else {
// If this is a new package in the process, add the package to the list
app.addPackage(info.packageName, info.versionCode, mProcessStats);
checkTime(startTime, "startProcess: added package to existing proc");
}
// If the system is not ready yet, then hold off on starting this
// process until it is.
if (!mProcessesReady
&& !isAllowedWhileBooting(info)
&& !allowWhileBooting) {
if (!mProcessesOnHold.contains(app)) {
mProcessesOnHold.add(app);
}
if (DEBUG_PROCESSES) Slog.v(TAG_PROCESSES,
"System not ready, putting on hold: " + app);
checkTime(startTime, "startProcess: returning with proc on hold");
return app;
}
checkTime(startTime, "startProcess: stepping in to startProcess");
final boolean success = startProcessLocked(app, hostingType, hostingNameStr, abiOverride);
checkTime(startTime, "startProcess: done starting proc!");
return success ? app : null;
}
- Process.start //在这里创建了新进程，新的进程会导入ActivityThread类，并执行它的main函数
第五阶段： 创建ActivityThread实例，执行一些初始化操作，并绑定Application。如果Application不存在，会调用LoadedApk.makeApplication创建一个新的Application对象。之后进入Loop循环。（执行在新创建的app进程）
- ActivityThread.main
- ActivityThread.attach(false) //声明不是系统进程
- ActivityManagerProxy.attachApplication
第六阶段：处理新的应用进程发出的创建进程完成的通信请求，并通知新应用程序进程启动目标Activity组件（执行在AMS进程）
- ActivityManagerService.attachApplication //AMS绑定本地ApplicationThread对象，后续通过ApplicationThreadProxy来通信。
- ActivityManagerService.attachApplicationLocked
- ActivityStack.realStartActivityLocked //真正要启动Activity了！
- ApplicationThreadProxy.scheduleLaunchActivity //AMS通过ATP通知app进程启动Activity
第七阶段： 加载MainActivity类，调用onCreate声明周期方法（执行在新启动的app进程）
- ApplicationThread.scheduleLaunchActivity //ApplicationThread发消息给AT
- ActivityThread.queueOrSendMessage
- H.handleMessage //AT的Handler来处理接收到的LAUNCH_ACTIVITY的消息
- ActivityThread.handleLaunchActivity
- ActivityThread.performLaunchActivity
- Instrumentation.newActivity //调用Instrumentation类来新建一个Activity对象
- Instrumentation.callActivityOnCreate
- MainActivity.onCreate
- ActivityThread.handleResumeActivity
- AMP.activityResumed
- AMS.activityResumed(AMS进程)