**
Fragment的onCreateView創建的view是如果加入到Activity的過程分析
**
1.簡單介紹一下fragment的使用
在activity的佈局裏添加一個ViewGroup並設置一個id，使用的時候通過這個id添加一個fragment。這個過程相信大家都非常的清楚所以很簡單的說明一下。
2.開始正式說明這個添加過程
1，在FragmentActivity裏有一個變量mFragments
final FragmentController mFragments = FragmentController.createController(new HostCallbacks());
這個mFragments 是用來管理控制fragment的，請看他的創建方法，new了一個HostCallbacks對象，這個對象是activity與fragmeController交互的回調
class HostCallbacks extends FragmentHostCallback<FragmentActivity> {
public HostCallbacks() {
super(FragmentActivity.this /*fragmentActivity*/);
}
@Override
public void onDump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
FragmentActivity.this.dump(prefix, fd, writer, args);
}
@Override
public boolean onShouldSaveFragmentState(Fragment fragment) {
return !isFinishing();
}
@Override
public LayoutInflater onGetLayoutInflater() {
return FragmentActivity.this.getLayoutInflater().cloneInContext(FragmentActivity.this);
}
@Override
public FragmentActivity onGetHost() {
return FragmentActivity.this;
}
@Override
public void onSupportInvalidateOptionsMenu() {
FragmentActivity.this.supportInvalidateOptionsMenu();
}
@Override
public void onStartActivityFromFragment(Fragment fragment, Intent intent, int requestCode) {
FragmentActivity.this.startActivityFromFragment(fragment, intent, requestCode);
}
@Override
public void onStartActivityFromFragment(
Fragment fragment, Intent intent, int requestCode, @Nullable Bundle options) {
FragmentActivity.this.startActivityFromFragment(fragment, intent, requestCode, options);
}
@Override
public void onStartIntentSenderFromFragment(Fragment fragment, IntentSender intent,
int requestCode, @Nullable Intent fillInIntent, int flagsMask, int flagsValues,
int extraFlags, Bundle options) throws IntentSender.SendIntentException {
FragmentActivity.this.startIntentSenderFromFragment(fragment, intent, requestCode,
fillInIntent, flagsMask, flagsValues, extraFlags, options);
}
@Override
public void onRequestPermissionsFromFragment(@NonNull Fragment fragment,
@NonNull String[] permissions, int requestCode) {
FragmentActivity.this.requestPermissionsFromFragment(fragment, permissions,
requestCode);
}
@Override
public boolean onShouldShowRequestPermissionRationale(@NonNull String permission) {
return ActivityCompat.shouldShowRequestPermissionRationale(
FragmentActivity.this, permission);
}
@Override
public boolean onHasWindowAnimations() {
return getWindow() != null;
}
@Override
public int onGetWindowAnimations() {
final Window w = getWindow();
return (w == null) ? 0 : w.getAttributes().windowAnimations;
}
@Override
public void onAttachFragment(Fragment fragment) {
FragmentActivity.this.onAttachFragment(fragment);
}
@Nullable
@Override
public View onFindViewById(int id) {
return FragmentActivity.this.findViewById(id);
}
@Override
public boolean onHasView() {
final Window w = getWindow();
return (w != null && w.peekDecorView() != null);
}
}
在這個回調的方法都很重要，其中
@Override
public FragmentActivity onGetHost() {
return FragmentActivity.this;
}
@Nullable
@Override
public View onFindViewById(int id) {
return FragmentActivity.this.findViewById(id);
}
這兩個方法是把fragment的view添加到activity最重要的2個方法，onFindViewById(int id)的這個id 就是
我們activity佈局時給fragment設置ViewGroup ID。
FragmentController 裏的private final FragmentHostCallback<?> mHost;就是通過onGetHost方法賦值。
FragmentHostCallback裏面的幾個重要變量
private final Activity mActivity;
final Context mContext;
private final Handler mHandler;
final int mWindowAnimations;
final FragmentManagerImpl mFragmentManager = new FragmentManagerImpl();
這幾個變量看名字也能猜出他們是幹什麼的，其中mFragmentManager 是主要負責管理fragment的各種操作，包括onCreateView這個方法
現在我們再看看FragmentManagerImpl這個類裏的2個重要變量
FragmentHostCallback mHost;
FragmentContainer mContainer;
mHost就是HostCallbacks 的實例對象
mContainer看名字是一個Fragment的容器，他的代碼如下：
public abstract class FragmentContainer {
/**
* Return the view with the given resource ID. May return {@code null} if the
* view is not a child of this container.
*/
@Nullable
public abstract View onFindViewById(@IdRes int id);
/**
* Return {@code true} if the container holds any view.
*/
public abstract boolean onHasView();
/**
* Creates an instance of the specified fragment, can be overridden to construct fragments
* with dependencies, or change the fragment being constructed. By default just calls
* {@link Fragment#instantiate(Context, String, Bundle)}.
*/
public Fragment instantiate(Context context, String className, Bundle arguments) {
return Fragment.instantiate(context, className, arguments);
}
}
instantiate用來創建fragment的實例，onFindViewById最後會通過
@Nullable
@Override
public View onFindViewById(int id) {
return FragmentActivity.this.findViewById(id);
}
這個方法來獲取我們給fragment準備的ViewGroup並添加fragment onCreateView返回的view，這樣fragment的view就添加到acti裏了
那有人可能就要問了mContainer是在哪初始化的，在FragmentManagerImpl的如下方法裏
public void attachController(FragmentHostCallback host,
FragmentContainer container, Fragment parent) {
if (mHost != null) throw new IllegalStateException("Already attached");
mHost = host;
mContainer = container;
mParent = parent;
}
再看看attachController是在哪調用的呢？這時又回到了FragmentController裏
public void attachHost(Fragment parent) {
mHost.mFragmentManager.attachController(
mHost, mHost /*container*/, parent);
}
mHost 是不是很熟悉，前面介紹過了
3.最後看看mContainer是怎麼添加view的
在FragmentManagerImpl的onCreateView方法裏，方法比較長這裏完整貼出方便看清楚過程
（說明一下這原碼是在android.support.v4.app包下找的，不同版本內容可能略有不同）
@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
if (!"fragment".equals(name)) {
return null;
}
String fname = attrs.getAttributeValue(null, "class");
TypedArray a = context.obtainStyledAttributes(attrs, FragmentTag.Fragment);
if (fname == null) {
fname = a.getString(FragmentTag.Fragment_name);
}
int id = a.getResourceId(FragmentTag.Fragment_id, View.NO_ID);
String tag = a.getString(FragmentTag.Fragment_tag);
a.recycle();
if (!Fragment.isSupportFragmentClass(mHost.getContext(), fname)) {
// Invalid support lib fragment; let the device's framework handle it.
// This will allow android.app.Fragments to do the right thing.
return null;
}
int containerId = parent != null ? parent.getId() : 0;
if (containerId == View.NO_ID && id == View.NO_ID && tag == null) {
throw new IllegalArgumentException(attrs.getPositionDescription()
+ ": Must specify unique android:id, android:tag, or have a parent with an id for " + fname);
}
// If we restored from a previous state, we may already have
// instantiated this fragment from the state and should use
// that instance instead of making a new one.
Fragment fragment = id != View.NO_ID ? findFragmentById(id) : null;
if (fragment == null && tag != null) {
fragment = findFragmentByTag(tag);
}
if (fragment == null && containerId != View.NO_ID) {
fragment = findFragmentById(containerId);
}
if (FragmentManagerImpl.DEBUG) Log.v(TAG, "onCreateView: id=0x"
+ Integer.toHexString(id) + " fname=" + fname
+ " existing=" + fragment);
if (fragment == null) {
fragment = mContainer.instantiate(context, fname, null);
fragment.mFromLayout = true;
fragment.mFragmentId = id != 0 ? id : containerId;
fragment.mContainerId = containerId;
fragment.mTag = tag;
fragment.mInLayout = true;
fragment.mFragmentManager = this;
fragment.mHost = mHost;
fragment.onInflate(mHost.getContext(), attrs, fragment.mSavedFragmentState);
addFragment(fragment, true);
} else if (fragment.mInLayout) {
// A fragment already exists and it is not one we restored from
// previous state.
throw new IllegalArgumentException(attrs.getPositionDescription()
+ ": Duplicate id 0x" + Integer.toHexString(id)
+ ", tag " + tag + ", or parent id 0x" + Integer.toHexString(containerId)
+ " with another fragment for " + fname);
} else {
// This fragment was retained from a previous instance; get it
// going now.
fragment.mInLayout = true;
fragment.mHost = mHost;
// If this fragment is newly instantiated (either right now, or
// from last saved state), then give it the attributes to
// initialize itself.
if (!fragment.mRetaining) {
fragment.onInflate(mHost.getContext(), attrs, fragment.mSavedFragmentState);
}
}
// If we haven't finished entering the CREATED state ourselves yet,
// push the inflated child fragment along. This will ensureInflatedFragmentView
// at the right phase of the lifecycle so that we will have mView populated
// for compliant fragments below.
if (mCurState < Fragment.CREATED && fragment.mFromLayout) {
moveToState(fragment, Fragment.CREATED, 0, 0, false);
} else {
moveToState(fragment);
}
if (fragment.mView == null) {
throw new IllegalStateException("Fragment " + fname
+ " did not create a view.");
}
if (id != 0) {
fragment.mView.setId(id);
}
if (fragment.mView.getTag() == null) {
fragment.mView.setTag(tag);
}
return fragment.mView;
}
在這個很長的方法裏通過fragment = mContainer.instantiate(context, fname, null);創建fragment，
通過 moveToState(fragment);來添加view。這個方法也很長裏面通過不同狀態進行不同的操作
這裏只貼出create的部分
case Fragment.CREATED:
// This is outside the if statement below on purpose; we want this to run
// even if we do a moveToState from CREATED => *, CREATED => CREATED, and
// * => CREATED as part of the case fallthrough above.
ensureInflatedFragmentView(f);
if (newState > Fragment.CREATED) {
if (DEBUG) Log.v(TAG, "moveto ACTIVITY_CREATED: " + f);
if (!f.mFromLayout) {
ViewGroup container = null;
if (f.mContainerId != 0) {
if (f.mContainerId == View.NO_ID) {
throwException(new IllegalArgumentException(
"Cannot create fragment "
+ f
+ " for a container view with no id"));
}
//通過id獲取activity的ViewGroup
container = (ViewGroup) mContainer.onFindViewById(f.mContainerId);
if (container == null && !f.mRestored) {
String resName;
try {
resName = f.getResources().getResourceName(f.mContainerId);
} catch (NotFoundException e) {
resName = "unknown";
}
throwException(new IllegalArgumentException(
"No view found for id 0x"
+ Integer.toHexString(f.mContainerId) + " ("
+ resName
+ ") for fragment " + f));
}
}
f.mContainer = container;
//調用fragment的onCreateView返回的view賦值
f.mView = f.performCreateView(f.performGetLayoutInflater(
f.mSavedFragmentState), container, f.mSavedFragmentState);
if (f.mView != null) {
f.mInnerView = f.mView;
f.mView.setSaveFromParentEnabled(false);
if (container != null) {
//把fragment創建的view添加到了activity的設置的ViewGroup裏
container.addView(f.mView);
}
if (f.mHidden) {
f.mView.setVisibility(View.GONE);
}
f.onViewCreated(f.mView, f.mSavedFragmentState);
dispatchOnFragmentViewCreated(f, f.mView, f.mSavedFragmentState,
false);
// Only animate the view if it is visible. This is done after
// dispatchOnFragmentViewCreated in case visibility is changed
f.mIsNewlyAdded = (f.mView.getVisibility() == View.VISIBLE)
&& f.mContainer != null;
} else {
f.mInnerView = null;
}
}
f.performActivityCreated(f.mSavedFragmentState);
dispatchOnFragmentActivityCreated(f, f.mSavedFragmentState, false);
if (f.mView != null) {
f.restoreViewState(f.mSavedFragmentState);
}
f.mSavedFragmentState = null;
}
關鍵部分加入了註釋，到這裏整個過程就都說了，希望對大家有用，哪裏時候的不對的請指出，謝謝