一.概述
當項目有加殼子,插件化或熱修復等需求的時候,可以使用Proxy/Delegate Application框架的方式,在正常的模式中,一個程序一般只有一個Application入口,而Proxy/Delegate模式中需要有兩個Application,原程序的Application改爲Delegate Application,再新加一個Proxy Application,由Proxy Application 提供一系列的個性化定製,再將所有的context和context相關的引用全部轉化爲Delegate
Application的實例,讓外界包括Delegate Application自身都以爲該App的Application入口就是Delegate Application.
二.實例
1.Proxy/Delegate 之前
這裏就在Android 4.4原生的DeskClock程序上應用Proxy/Delegate框架爲示例
原生的DeskClock程序沒有自定義Application,這裏先定義一個,並print該程序目前ApplicationContext的名字(在DeskClock中使用的Log是自定義的)
/**
* Created by jesse on 15-7-17.
*/
public class MyApplication extends Application{
private final String TAG = MyApplication.class.getSimpleName();
@Override
public void onCreate() {
super.onCreate();
Log.i(TAG + ", onCreate " + this.getApplicationContext().getClass().getSimpleName());
}
} Application的Manifest配置是
<application android:name="cn.jesse.MyApplication"
android:label="@string/app_label"
android:icon="@mipmap/ic_launcher_alarmclock"
android:requiredForAllUsers="true"
android:supportsRtl="true">
2.使用Proxy/Delegate框架之後
使用Proxy/Delegate框架,需要重新構建出來一個新的ProxyApplication,用來做代理Application,原先的MyApplication的作用爲DelegateApplication
所以Manifest的配置需要更改,app的主入口更改爲MyProxyApplication,把DelegateApplication的信息以meta-data子元素的形式存儲(當然也可以用其他的方式)
<application android:name="cn.jesse.MyProxyApplication"
android:label="@string/app_label"
android:icon="@mipmap/ic_launcher_alarmclock"
android:requiredForAllUsers="true"
android:supportsRtl="true">
<meta-data
android:name="DELEGATE_APPLICATION_CLASS_NAME"
android:value="cn.jesse.MyApplication" >
</meta-data>
</application> 定義一個抽象類,提供一個用於替換當前ProxyApplication 的ClassLoader成父類的ClassLoader的抽象方法(或者一些其他的個性化定製)
* Created by jesse on 15-7-17.
*/
public abstract class ProxyApplication extends Application{
protected abstract void initProxyApplication();
} 通常來說在Application的OnCreate中來做替換就足夠了,但是當app有註冊ContentProvider的時候ContentProvider：OnCreate的調用是在Application:OnCreate之前的,所以我們必須保證替換ClassLoader的動作要在ContentProvider之前.
通過查看源碼可以看到Application是繼承自ContextWrapper,而在ContextWrapper中系統在構建完成完善的Context之後第一次回調是通過attachBaseContext方法,既然這樣就通過在ProxyApplication中複寫該方法來獲取剛出爐熱噴噴的Context來轉換ClassLoader.
/**
* Set the base context for this ContextWrapper. All calls will then be
* delegated to the base context. Throws
* IllegalStateException if a base context has already been set.
*
* @param base The new base context for this wrapper.
*/
protected void attachBaseContext(Context base) {
if (mBase != null) {
throw new IllegalStateException("Base context already set");
}
mBase = base;
}/**
* Created by jesse on 15-7-17.
*/
public class MyProxyApplication extends ProxyApplication {
private final String TAG = MyProxyApplication.class.getSimpleName();
private Context mContext;
@Override
protected void attachBaseContext(Context base) {
super.attachBaseContext(base);
Log.i(TAG + ", attachBaseContext");
mContext = base;
this.initProxyApplication();
}
@Override
public void onCreate() {
super.onCreate();
Log.i(TAG + ", onCreate" + this.getApplicationContext().getClass().getSimpleName());
BootLoader.boot(mContext);
}
@Override
protected void initProxyApplication() {
Log.i(TAG + ", initProxyApplication");
BootLoader.resetClassLoader(mContext);
}
}
入口的順序沒問題了之後,就可以在initProxyApplication方法中替換當前的ClassLoader到父類的ClassLoader,並且在MyProxyApplication的onCreate中將應用層所有的Application的引用全部從ProxyApplication替換成MyApplication(當前在DeskClock程序中沒有替換ClassLoader的需求,只需要替換所有的Application的引用就能達到代理的效果,所以在initProxyApplication方法處就寫了一個空方法帶過).
先從AndroidManifest配置文件中的metadata拿到DelegateApplication的屬性
String className = CLASS_NAME;
ApplicationInfo appInfo = getPackageManager().getApplicationInfo(super.getPackageName(), PackageManager.GET_META_DATA);
Bundle bundle = appInfo.metaData;
if (bundle != null && bundle.containsKey(KEY)) {
className = bundle.getString(KEY);
if (className.startsWith("."))
className = super.getPackageName() + className;
} Class delegateClass = Class.forName(className, true, getClassLoader());
Application delegate = (Application) delegateClass.newInstance();
Application proxyApplication = (Application)getApplicationContext(); Class contextImplClass = Class.forName("android.app.ContextImpl");
Field mOuterContext = contextImplClass.getDeclaredField("mOuterContext");
mOuterContext.setAccessible(true);
mOuterContext.set(mContext, delegate); 獲取MyProxyApplication Context的PackageInfo對象,替換掉其中的mApplication屬性
Field mPackageInfoField = contextImplClass.getDeclaredField("mPackageInfo");
mPackageInfoField.setAccessible(true);
Object mPackageInfo = mPackageInfoField.get(mContext);
Class loadedApkClass = Class.forName("android.app.LoadedApk");
Field mApplication = loadedApkClass.getDeclaredField("mApplication");
mApplication.setAccessible(true);
mApplication.set(mPackageInfo, delegate); 再根據之前反射得到的packageInfo對象獲取到mActivityThread屬性,替換掉其中的mInitialApplication屬性
Class activityThreadClass = Class.forName("android.app.ActivityThread");
Field mAcitivityThreadField = loadedApkClass.getDeclaredField("mActivityThread");
mAcitivityThreadField.setAccessible(true);
Object mActivityThread = mAcitivityThreadField.get(mPackageInfo);
Field mInitialApplicationField = activityThreadClass.getDeclaredField("mInitialApplication");
mInitialApplicationField.setAccessible(true);
mInitialApplicationField.set(mActivityThread, delegate); 拿着之前的mActivityThread對象獲取到mAllApplications屬性,注意該屬性是一個list，這裏就移除MyProxyApplication添加DelegateApplication,至此應用層MyProxyApplication的Context的引用全部都替換成了MyApplication的引用.
Field mAllApplicationsField = activityThreadClass.getDeclaredField("mAllApplications");
mAllApplicationsField.setAccessible(true);
ArrayList<Application> al = (ArrayList<Application>)mAllApplicationsField.get(mActivityThread);
al.add(delegate);
al.remove(proxyApplication); 給MyApplication通過反射和attach內部方法設置baseContext,並調用MyApplication的onCreate方法完成DelegateApplication的初始化.
Method attach = Application.class.getDeclaredMethod("attach", Context.class);
attach.setAccessible(true);
attach.invoke(delegate, mContext);
delegate.onCreate();
但是這樣還沒有完全結束,還記得開頭說的ContentProvider嗎?他的構造是在Application的onCreate之前的,那麼ContentProvider部分有沒有需要替換的Context引用呢？從framework/base/core/java/android/app下可以找到ActivityThread.java從其中裝載ContentProvider的部分可以看到,如果當前Context的包名和ProviderInfo的包名一樣的話,ContentProvider就會引用當前的MyProxyApplication的Context.由於當前的MyProxyApplication只是做代理啓動用的,所以在MyProxyApplication處複寫getPackageName並且返回空就可以避免ContentProvider複用當前Context了.
private IActivityManager.ContentProviderHolder installProvider(Context context,
IActivityManager.ContentProviderHolder holder, ProviderInfo info,
boolean noisy, boolean noReleaseNeeded, boolean stable) {
ContentProvider localProvider = null;
IContentProvider provider;
if (holder == null || holder.provider == null) {
if (DEBUG_PROVIDER || noisy) {
Slog.d(TAG, "Loading provider " + info.authority + ": "
+ info.name);
}
Context c = null;
ApplicationInfo ai = info.applicationInfo;
if (context.getPackageName().equals(ai.packageName)) {
c = context;
} else if (mInitialApplication != null &&
mInitialApplication.getPackageName().equals(ai.packageName)) {
c = mInitialApplication;
} else {
try {
c = context.createPackageContext(ai.packageName,
Context.CONTEXT_INCLUDE_CODE);
} catch (PackageManager.NameNotFoundException e) {
// Ignore
}
}三.總結
這篇只是先簡單的走了下Proxy/Delegate框架的流程,這個框架其實是有很多使用場景的,例如多dex動態加載,插件化,線上程序熱修復bug等可以靈活使用出很多有趣的技術,有時間的話還會再發一篇以Proxy/Delegate實現的線上程序熱修復bug的博客.
轉載請註明出處:http://blog.csdn.net/l2show/article/details/46914881
