本文最早發佈在CSDN博客,地址:http://blog.csdn.net/hwliu51/article/details/69841068。 歡迎轉載,但請標明原文地址。java
==本文所引用的代碼均爲support-v4-23.0.1包中的源碼,使用‘...’表示省略部分代碼。==數組
當在Activity的onCreate方法中經過一下方式添加Fragment,運行程序,即可以修飾在屏幕上。ide
FragmentManager fm = getSupportFragmentManager(); FragmentTransaction transaction = fm.beginTransaction(); transaction.add(resId, fragmentA); transaction.commit();
這幾行代碼讓Fragment經歷了怎樣的一番旅途,最終被關聯到宿主Activity並顯示。我準備扒一扒support-v4-23.0.0的源碼,探索這一段神奇的旅途。oop
##一 相關的類##佈局
與此相關的類主要有10個,分別爲:post
FragmentManger爲抽象類,定義對Fragment的操做行爲,子類爲FragmentMangerImpl。FragmentMangerImpl又實現了LayoutInflaterFactory接口,是真正對Fragment執行初始化,顯示和移除等等操做的類。ui
FragmentTransaction爲抽象類,定義對Fragment操做事務行爲,子類爲BackStackRecord。BackStackRecord又實現了Runnable和FragmentManger.BackStackEntry接口,是執行Fragment添加,顯示,隱藏和移除等等事務的類。Op爲BackStackRecord的靜態內部類,當使用FragmentTransaction添加,替換,隱藏,移除等等操做便會在BackStackRecord對象中生成一個記錄操做行爲和Fragment的Op對象,該對象以鏈表的方式存儲在BackStackRecord中。this
FragmentHostCallback<E>爲抽象類,又繼承了FragmentContainer,子類爲FragmentActivity的內部類HostCallback。spa
FragmentController封裝對FragmentMangerImpl和HostCallback獲取和操做的方法。.net
FragmentActivity用做Fragment的容器。
類圖(待添加):
##流程分析 ###一,獲取FragmentManager 在咱們自定義的Activity中常常使用使用getSupportFragmentManager方法獲取當前的FragmentManager(即FragmentMagagerImpl對象),那就先看看FragmentActivity類中的代碼:
public FragmentManager getSupportFragmentManager() { return mFragments.getSupportFragmentManager(); }
mFragments是什麼類型,什麼時候初始化與賦值?接着往FragmentActivity中查看:
//在對象建立是便已賦值 final FragmentController mFragments = FragmentController.createController(new HostCallbacks());
建立HostCallbacks對象,那就看看它的構造方法代碼:
public HostCallbacks() { //調用父類FragmentHostCallback的構造方法進行初始化 super(FragmentActivity.this /*fragmentActivity*/); }
接着繼續看FragmentHostCallback代碼:
public abstract class FragmentHostCallback<E> extends FragmentContainer { //當前關聯的FragmentActivity對象 private final Activity mActivity; //當前關聯的Context對象,其實就是FragmentActivity對象 final Context mContext; //當前FragmentActivity的mHandler屬性 private final Handler mHandler; final int mWindowAnimations; //FragmentActivity獲取的FragmentManager就是這個屬性 final FragmentManagerImpl mFragmentManager = new FragmentManagerImpl(); //當前key爲who,value爲加載器LoaderManagerImpl private SimpleArrayMap<String, LoaderManager> mAllLoaderManagers; // private LoaderManagerImpl mLoaderManager; private boolean mCheckedForLoaderManager; private boolean mLoadersStarted; public FragmentHostCallback(Context context, Handler handler, int windowAnimations) { this(null /*activity*/, context, handler, windowAnimations); } //FragmentActivity的內部類HostCallbacks調用賦值的構造方法 FragmentHostCallback(FragmentActivity activity) { //使用activity給mContext賦值,activity.mHandler給mHandler賦值 this(activity, activity /*context*/, activity.mHandler, 0 /*windowAnimations*/); } //執行賦值 FragmentHostCallback(Activity activity, Context context, Handler handler, int windowAnimations) { Activity = activity; mContext = context; mHandler = handler; mWindowAnimations = windowAnimations; } ... }
再往回看看FragmentActivity的onCreate方法:
protected void onCreate(@Nullable Bundle savedInstanceState) { //**這一步很重要** //將FragmentController的mHost賦值給HostCallBack的mFragmentManager,便完成了當前Activity與FramgmentManger關聯。 mFragments.attachHost(null /*parent*/); super.onCreate(savedInstanceState); NonConfigurationInstances nc = (NonConfigurationInstances) getLastNonConfigurationInstance(); if (nc != null) { mFragments.restoreLoaderNonConfig(nc.loaders); } if (savedInstanceState != null) { Parcelable p = savedInstanceState.getParcelable(FRAGMENTS_TAG); mFragments.restoreAllState(p, nc != null ? nc.fragments : null); } //通知mFragmentManager當前Activity執行了onCreate mFragments.dispatchCreate(); }
FragmentController中attachHost和dispatchCreate方法代碼:
public void attachHost(Fragment parent) { mHost.mFragmentManager.attachController(mHost, mHost /*container*/, parent); } public void dispatchCreate() { mHost.mFragmentManager.dispatchCreate(); }
調用FragmentManagerImpl相關方法和屬性的代碼:
public void attachController(FragmentHostCallback host, FragmentContainer container, Fragment parent) { if (mHost != null) throw new IllegalStateException("Already attached"); //將FragmentController中的mHost賦值給FragmentManagerImpl的mHost,自此便完成當前Activity與FramgmentManger關聯 mHost = host; mContainer = container; mParent = parent; } //FragmentManagerImpl當前狀態值,默認爲初始化 int mCurState = Fragment.INITIALIZING; public void dispatchCreate() { mStateSaved = false; //更新當前狀態mCurState爲Fragment.CREATED moveToState(Fragment.CREATED, false); } void moveToState(int newState, boolean always) { moveToState(newState, 0, 0, always); } void moveToState(int newState, int transit, int transitStyle, boolean always) { if (mHost == null && newState != Fragment.INITIALIZING) { throw new IllegalStateException("No host"); } if (!always && mCurState == newState) { return; } //更新當前狀態mCurState爲Fragment.CREATED mCurState = newState; //當從FragmentActivity的onCreate執行到此時,因爲還未有添加Fragment,則mActive爲null,便返回。 //執行完這些代碼後,FragmentManagerImpl的mCurState爲Fragment.CREATED if (mActive != null) { boolean loadersRunning = false; for (int i=0; i<mActive.size(); i++) { Fragment f = mActive.get(i); if (f != null) { moveToState(f, newState, transit, transitStyle, false); ... } } ... } }
當Activity的onCreate方法執行完super.onCreate(),咱們便可以經過getSupportFragmentManager方法獲取到一個能夠正常使用的FragmentManagerImpl對象。
###二,獲取FragmentTransaction 調用FragmentManager的beginTransaction()方法獲取FragmentTransaction。看看代碼,究竟執行了哪些操做。
public FragmentTransaction beginTransaction() { //建立了一個BackStackRecord對象,並把本身做爲參數傳遞給它。 return new BackStackRecord(this); } public BackStackRecord(FragmentManagerImpl manager){ //對mManager進行賦值,完成BackStackRecord與FragmentManagerImpl關聯 mManager = manager; }
###三,添加Fragment 調用FragmentTransaction的add方法添加Fragment又執行了BackStackRecord哪些方法?繼續看代碼:
//添加Fragment並綁定tag public FragmentTransaction add(Fragment fragment, String tag) { doAddOp(0, fragment, tag, OP_ADD); return this; } //向指定id的View做爲容器,添加Fragment public FragmentTransaction add(int containerViewId, Fragment fragment) { doAddOp(containerViewId, fragment, null, OP_ADD); return this; } //指定View容器和tag,添加Fragment public FragmentTransaction add(int containerViewId, Fragment fragment, String tag) { doAddOp(containerViewId, fragment, tag, OP_ADD); return this; } private void doAddOp(int containerViewId, Fragment fragment, String tag, int opcmd) { //將與Activity關聯的FragmentMangerImpl對象賦值給Fragment fragment.mFragmentManager = mManager; //若是Fragment的tag屬性已賦值,則添加時指定的tag必需要與其相同 if (tag != null) { if (fragment.mTag != null && !tag.equals(fragment.mTag)) { throw new IllegalStateException("Can't change tag of fragment " + fragment + ": was " + fragment.mTag + " now " + tag); } fragment.mTag = tag; } //若是Fagment已關聯顯示容器的Id(即在View中顯示),則添加時不能添加到其餘的View if (containerViewId != 0) { if (fragment.mFragmentId != 0 && fragment.mFragmentId != containerViewId) { throw new IllegalStateException("Can't change container ID of fragment " + fragment + ": was " + fragment.mFragmentId + " now " + containerViewId); } fragment.mContainerId = fragment.mFragmentId = containerViewId; } //建立Op,指定執行操做類型和關聯Fragment Op op = new Op(); op.cmd = opcmd; op.fragment = fragment; addOp(op); } //將Op對象加入到Op鏈表中 void addOp(Op op) { if (mHead == null) { mHead = mTail = op; } else { //加入到Op鏈表尾部 op.prev = mTail; mTail.next = op; mTail = op; } ... mNumOp++; }
自此Fragment便被添加到FragmentTransaction(即BackStackRecord對象中)。
###四,提交Fragment添加事務 調用FragmentTransaction的commit方法,便提交Fragment的添加事務。咱們只要運行代碼,Fragment便會顯示在屏幕上。commit操做執行了哪些方法,commit以後Actvity執行onStart和onResume時Fragment又經歷了哪些操做。繼續看代碼分析。
public int commit() { return commitInternal(false); } public int commitAllowingStateLoss() { return commitInternal(true); } int commitInternal(boolean allowStateLoss) { if (mCommitted) throw new IllegalStateException("commit already called"); if (FragmentManagerImpl.DEBUG) { Log.v(TAG, "Commit: " + this); LogWriter logw = new LogWriter(TAG); PrintWriter pw = new PrintWriter(logw); dump(" ", null, pw, null); } mCommitted = true; if (mAddToBackStack) { mIndex = mManager.allocBackStackIndex(this); } else { mIndex = -1; } //將建立的BackStackRecord對象,提交給FragmentManagerImpl mManager.enqueueAction(this, allowStateLoss); return mIndex; }
由於BackStackRecord實現了Runnable,故在FragmentManagerImpl定義一個ArrayList<Runnable>類型的集合mPendingActions來存儲添加的BackStackRecord對象。在看看enqueueAction以及與其相關的方法和屬性的代碼:
private void checkStateLoss() { //若是在已執行了保存狀態信息操做後執行commit,則拋出異常 if (mStateSaved) { throw new IllegalStateException( "Can not perform this action after onSaveInstanceState"); } if (mNoTransactionsBecause != null) { throw new IllegalStateException( "Can not perform this action inside of " + mNoTransactionsBecause); } } public void enqueueAction(Runnable action, boolean allowStateLoss) { //是否容許狀態信息丟失 if (!allowStateLoss) { //檢查狀態 checkStateLoss(); } synchronized (this) { if (mDestroyed || mHost == null) { throw new IllegalStateException("Activity has been destroyed"); } if (mPendingActions == null) { mPendingActions = new ArrayList<Runnable>(); } //將提交的BackStackRecord添加到集合中 mPendingActions.add(action); if (mPendingActions.size() == 1) { //移除還未執行的Runnalbe:mExecCommit mHost.getHandler().removeCallbacks(mExecCommit); //發送一個延時執行的Runnalbe:mExecCommit mHost.getHandler().post(mExecCommit); } } } //延時執行的Runnable對象 Runnable mExecCommit = new Runnable() { @Override public void run() { //運行mPendingActions中的Runnable對象 execPendingActions(); } };
從enqueueAction中第一個判斷的checkStateLoss方法代碼可知:不能在Activity執行onSaveInstanceState操做後再調用commit。若是提交的Fragment顯示重要的信息,建議也儘可能不要使用commitAllowingStateLoss。由於執行onSaveInstanceState時會保存全部Fragment的狀態信息 ,在其後執行commitAllowingStateLoss則會丟失提交的Fragment信息,致使狀態恢復時出現一些很奇怪的現象。
執行commit提交的BackStackRecord在enqueueAction方法裏並無被直接執行,而是存儲在mPendingActions中等待執行。同時,會移除正在Message隊列中等待執行的mExecCommit,並使用FragmentActivity的mHandler發送新的的延時執行信息mExecCommit。mExecCommit的run方法調用了execPendingActions,也就是說真正執行BackStackRecord的是execPendingActions。execPendingActions方法中有一個while(true)循環來遍歷mPendingActions中的Runnable並執行run方法,直至mPendingActions爲空集合才退出。
execPendingActions方法代碼:
/** * Only call from main thread! */ public boolean execPendingActions() { if (mExecutingActions) { throw new IllegalStateException("Recursive entry to executePendingTransactions"); } //不能在非主線程中調用此方法 if (Looper.myLooper() != mHost.getHandler().getLooper()) { throw new IllegalStateException("Must be called from main thread of process"); } boolean didSomething = false; //採用無限循環可讓在執行execPendingActions時提交的BackStackRecord被及時執行run方法。 while (true) { int numActions; synchronized (this) { //若是mPendingActions爲null(即未提交BackStackRecord),或mPendingActions爲空集合(即全部的BackStackRecord都執行完),則退出循環。 if (mPendingActions == null || mPendingActions.size() == 0) { break; } numActions = mPendingActions.size(); if (mTmpActions == null || mTmpActions.length < numActions) { mTmpActions = new Runnable[numActions]; } //將mPendingActions集合中的數據存儲到mTmpActions數組 mPendingActions.toArray(mTmpActions); //清空集合 mPendingActions.clear(); //移除延時執行消息 mHost.getHandler().removeCallbacks(mExecCommit); } mExecutingActions = true; for (int i=0; i<numActions; i++) { //**這一步執行很重要** //執行BackStackRecord的run方法 mTmpActions[i].run(); mTmpActions[i] = null; } mExecutingActions = false; didSomething = true; } ... return didSomething; }
關鍵步驟mTmpActions[i].run()執行的是BackStackRecord的run方法。其代碼:
public void run() { ... //循環執行Op鏈表中的Op對象 Op op = mHead; while (op != null) { int enterAnim = state != null ? 0 : op.enterAnim; int exitAnim = state != null ? 0 : op.exitAnim; switch (op.cmd) { //添加Fragment case OP_ADD: { Fragment f = op.fragment; f.mNextAnim = enterAnim; mManager.addFragment(f, false); } break; //替換Fragment case OP_REPLACE: { Fragment f = op.fragment; int containerId = f.mContainerId; if (mManager.mAdded != null) { for (int i=0; i<mManager.mAdded.size(); i++) { Fragment old = mManager.mAdded.get(i); if (FragmentManagerImpl.DEBUG) Log.v(TAG, "OP_REPLACE: adding=" + f + " old=" + old); if (old.mContainerId == containerId) { if (old == f) { op.fragment = f = null; } else { if (op.removed == null) { op.removed = new ArrayList<Fragment>(); } op.removed.add(old); old.mNextAnim = exitAnim; if (mAddToBackStack) { old.mBackStackNesting += 1; if (FragmentManagerImpl.DEBUG) Log.v(TAG, "Bump nesting of " + old + " to " + old.mBackStackNesting); } mManager.removeFragment(old, transition, transitionStyle); } } } } if (f != null) { f.mNextAnim = enterAnim; mManager.addFragment(f, false); } } break; // case OP_REMOVE: { Fragment f = op.fragment; f.mNextAnim = exitAnim; mManager.removeFragment(f, transition, transitionStyle); } break; //隱藏Fragment case OP_HIDE: { Fragment f = op.fragment; f.mNextAnim = exitAnim; mManager.hideFragment(f, transition, transitionStyle); } break; //顯示Fragment case OP_SHOW: { Fragment f = op.fragment; f.mNextAnim = enterAnim; mManager.showFragment(f, transition, transitionStyle); } break; //detach Fragment case OP_DETACH: { Fragment f = op.fragment; f.mNextAnim = exitAnim; mManager.detachFragment(f, transition, transitionStyle); } break; //attach Fragment case OP_ATTACH: { Fragment f = op.fragment; f.mNextAnim = enterAnim; mManager.attachFragment(f, transition, transitionStyle); } break; default: { throw new IllegalArgumentException("Unknown cmd: " + op.cmd); } } //執行下一個Op對象 op = op.next; } //調用FragmentManagerImpl的moveToState,更新當前Fragment狀態 mManager.moveToState(mManager.mCurState, transition, transitionStyle, true); ... }
使用FragmentTransaction的add方法添加Fragment時,會建立Op對象,cmd爲OP_ADD。執行到此run方法時,則會進入case OP_ADD,在其中調用了FragmentManagerImpl的addFragment方法添加提交的Fragment。回顧一下以前FragmentActivity的onCreate中的介紹,當咱們在Activity的onCreate方法代碼super.onCreate後調用getSupportFragmentManager時,與Actvity關聯的FragmentManagerImpl對象的mCurState已被更新爲Fragment.CREATED。此時被提交的fragment的mState屬性仍是Fragment.INITIALIZING默認值。
繼續查看FragmentManagerImpl的addFragment方法和與其相關聯的makeActive方法代碼:
void makeActive(Fragment f) { if (f.mIndex >= 0) { return; } if (mAvailIndices == null || mAvailIndices.size() <= 0) { if (mActive == null) { mActive = new ArrayList<Fragment>(); } //設置其位置和父Fragment(在Activity中添加的,mParent爲null;只有在Fragment中添加的纔有Parent Fragment)。 f.setIndex(mActive.size(), mParent); //添加到mActive集合中 mActive.add(f); } else { //更新信息 f.setIndex(mAvailIndices.remove(mAvailIndices.size()-1), mParent); mActive.set(f.mIndex, f); } ... } public void addFragment(Fragment fragment, boolean moveToStateNow) { if (mAdded == null) { mAdded = new ArrayList<Fragment>(); } if (DEBUG) Log.v(TAG, "add: " + fragment); //添加到mActive或更新信息 makeActive(fragment); if (!fragment.mDetached) { //若是已添加到mAdd,則拋出異常 if (mAdded.contains(fragment)) { throw new IllegalStateException("Fragment already added: " + fragment); } //添加到mAdded mAdded.add(fragment); //修改標誌mAdded爲true(即已添加) fragment.mAdded = true; fragment.mRemoving = false; ... if (moveToStateNow) { //更新fragment狀態,並執行相應操做 moveToState(fragment); } } }
由於BackStackRecord的run方法中case OP_ADD代碼塊中的addFragment的moveToStateNow爲false,因此if (moveToStateNow)不成立,即不會進入moveToState(fragment)。待BackStackRecord的run方法中的Op鏈表的數據被執行完,便會執行底部代碼:mManager.moveToState(mManager.mCurState, transition, transitionStyle, true)。此時mManager.mCurState爲Fragment.CREATED,而fragment.mState爲Fragment.INITIALIZING。
初始化Fragment:
void moveToState(int newState, int transit, int transitStyle, boolean always) { … mCurState = newState; if (mActive != null) { boolean loadersRunning = false; //遍歷mActive集合 for (int i=0; i<mActive.size(); i++) { //獲取Fragment Fragment f = mActive.get(i); if (f != null) { //執行更新操做並更新f.mState moveToState(f, newState, transit, transitStyle, false); … } } … } }
調用mManager.moveToState傳入newState值與mCurState相同,mCurState值沒有被改變。執行moveToState(f, newState, transit, transitStyle, false)代碼。仍是繼續看代碼,分析。
先看看Fragment的幾種狀態值:
static final int INITIALIZING = 0; // Not yet created. static final int CREATED = 1; // Created. static final int ACTIVITY_CREATED = 2; // The activity has finished its creation. static final int STOPPED = 3; // Fully created, not started. static final int STARTED = 4; // Created and started, not resumed. static final int RESUMED = 5; // Created started and resumed.
當前FragmentManagerImpl的mCurState爲Fragment.CREATED(即1),而mAtive中的Fragment的mState爲Fragment.INITIALIZING(即0)。
void moveToState(Fragment f, int newState, int transit, int transitionStyle, boolean keepActive) { ... if (f.mState < newState) { // For fragments that are created from a layout, when restoring from // state we don't want to allow them to be created until they are // being reloaded from the layout. //若是f是從佈局文件建立的,當恢復狀態時,沒有執行執行從佈局從新加載操做,則返回 if (f.mFromLayout && !f.mInLayout) { return; } ... switch (f.mState) { //執行Fragment初始化 case Fragment.INITIALIZING: //若是有保存狀態信息,則恢復 if (f.mSavedFragmentState != null) { f.mSavedFragmentState.setClassLoader(mHost.getContext().getClassLoader()); f.mSavedViewState = f.mSavedFragmentState.getSparseParcelableArray( FragmentManagerImpl.VIEW_STATE_TAG); f.mTarget = getFragment(f.mSavedFragmentState, FragmentManagerImpl.TARGET_STATE_TAG); if (f.mTarget != null) { f.mTargetRequestCode = f.mSavedFragmentState.getInt( FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG, 0); } f.mUserVisibleHint = f.mSavedFragmentState.getBoolean( FragmentManagerImpl.USER_VISIBLE_HINT_TAG, true); if (!f.mUserVisibleHint) { f.mDeferStart = true; if (newState > Fragment.STOPPED) { newState = Fragment.STOPPED; } } } //mHost賦值FragemntContooler,即與Activity關聯 f.mHost = mHost; //設置父Fragemnt(默認爲null,只有子Fragemnt纔有值) f.mParentFragment = mParent; //關聯FragmentManagerImpl f.mFragmentManager = mParent != null ? mParent.mChildFragmentManager : mHost.getFragmentManagerImpl(); f.mCalled = false; f.onAttach(mHost.getContext()); if (!f.mCalled) { throw new SuperNotCalledException("Fragment " + f + " did not call through to super.onAttach()"); } if (f.mParentFragment == null) { mHost.onAttachFragment(f); } if (!f.mRetaining) { f.performCreate(f.mSavedFragmentState); } f.mRetaining = false; //從佈局文件建立的Fragemnt if (f.mFromLayout) { // For fragments that are part of the content view // layout, we need to instantiate the view immediately // and the inflater will take care of adding it. f.mView = f.performCreateView(f.getLayoutInflater( f.mSavedFragmentState), null, f.mSavedFragmentState); if (f.mView != null) { f.mInnerView = f.mView; if (Build.VERSION.SDK_INT >= 11) { ViewCompat.setSaveFromParentEnabled(f.mView, false); } else { f.mView = NoSaveStateFrameLayout.wrap(f.mView); } if (f.mHidden) f.mView.setVisibility(View.GONE); f.onViewCreated(f.mView, f.mSavedFragmentState); } else { f.mInnerView = null; } } //建立Fragment的View case Fragment.CREATED: if (newState > Fragment.CREATED) { if (DEBUG) Log.v(TAG, "moveto ACTIVITY_CREATED: " + f); //非佈局文件建立,即直接new if (!f.mFromLayout) { ViewGroup container = null; if (f.mContainerId != 0) { container = (ViewGroup)mContainer.onFindViewById(f.mContainerId); if (container == null && !f.mRestored) { throwException(new IllegalArgumentException( "No view found for id 0x" + Integer.toHexString(f.mContainerId) + " (" + f.getResources().getResourceName(f.mContainerId) + ") for fragment " + f)); } } f.mContainer = container; //執行建立View f.mView = f.performCreateView(f.getLayoutInflater( f.mSavedFragmentState), container, f.mSavedFragmentState); if (f.mView != null) { f.mInnerView = f.mView; if (Build.VERSION.SDK_INT >= 11) { ViewCompat.setSaveFromParentEnabled(f.mView, false); } else { f.mView = NoSaveStateFrameLayout.wrap(f.mView); } if (container != null) { Animation anim = loadAnimation(f, transit, true, transitionStyle); if (anim != null) { setHWLayerAnimListenerIfAlpha(f.mView, anim); f.mView.startAnimation(anim); } container.addView(f.mView); } if (f.mHidden) f.mView.setVisibility(View.GONE); f.onViewCreated(f.mView, f.mSavedFragmentState); } else { f.mInnerView = null; } } f.performActivityCreated(f.mSavedFragmentState); if (f.mView != null) { f.restoreViewState(f.mSavedFragmentState); } f.mSavedFragmentState = null; } //執行Fragment的start操做 case Fragment.ACTIVITY_CREATED: case Fragment.STOPPED: if (newState > Fragment.STOPPED) { if (DEBUG) Log.v(TAG, "moveto STARTED: " + f); f.performStart(); } //顯示Fragemnt case Fragment.STARTED: if (newState > Fragment.STARTED) { if (DEBUG) Log.v(TAG, "moveto RESUMED: " + f); f.mResumed = true; f.performResume(); f.mSavedFragmentState = null; f.mSavedViewState = null; } } } else if (f.mState > newState) { ... } //更新fragment的mState值 f.mState = newState; }
執行moveToState(f, newState, transit, transitStyle, false)代碼時,傳入的newState爲1,而f.mState爲0,則進入case Fragment.INITIALIZING代碼塊。待執行完Fragment.INITIALIZING代碼塊,因爲f.mState值比Fragment.CREATED,Fragment.ACTIVITY_CREATED,Fragment.STOPPED和Fragment.STARTED都小,則沒法進入這些代碼塊。最終執行f.mState = newState,更新f.mState爲Fragment.CREATED。
到此時Activity的代碼也剛執行完onCreate,接着執行onStart,onResume並顯示。接着看FragemntActivity中的這些方法代碼:
final Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { ... case MSG_RESUME_PENDING: onResumeFragments(); //遍歷並執行execPendingActions中BackStackRecord mFragments.execPendingActions(); break; default: super.handleMessage(msg); } } }; protected void onStart() { super.onStart(); ... if (!mCreated) { mCreated = true; //更新狀態爲ActivityCreated mFragments.dispatchActivityCreated(); } mFragments.noteStateNotSaved(); //遍歷並執行execPendingActions中BackStackRecord mFragments.execPendingActions(); mFragments.doLoaderStart(); //更新狀態爲Start mFragments.dispatchStart(); mFragments.reportLoaderStart(); } protected void onResume() { super.onResume(); //發送執行execPendingActions消息 mHandler.sendEmptyMessage(MSG_RESUME_PENDING); mResumed = true; //遍歷並執行execPendingActions中BackStackRecord mFragments.execPendingActions(); }
FragmentController中execPendingActions,dispatchActivityCreated和dispatchStart代碼:
public void dispatchActivityCreated() { mHost.mFragmentManager.dispatchActivityCreated(); } public void dispatchStart() { mHost.mFragmentManager.dispatchStart(); } public void dispatchResume() { mHost.mFragmentManager.dispatchResume(); } public boolean execPendingActions() { return mHost.mFragmentManager.execPendingActions(); }
FragmentController並無作什麼事情,而是FragmentManagerImpl執行了對應的操做。再看看FragmentManagerImpl中這些方法的代碼。execPendingActions方法代碼在上文有展現,此處便再也不列出。
public void dispatchActivityCreated() { mStateSaved = false; moveToState(Fragment.ACTIVITY_CREATED, false); } public void dispatchStart() { mStateSaved = false; moveToState(Fragment.STARTED, false); } public void dispatchResume() { mStateSaved = false; moveToState(Fragment.RESUMED, false); }
當執行moveToState(Fragment.ACTIVITY_CREATED, false), 則FragmentManagerImpl的mCurState更新爲ACTIVITY_CREATED,Fragment便會進入到case Fragment.CREATED代碼塊,執行create相關操做。依次類推Activity執行onResume,fragment執行performResume()便可以顯示在屏幕上。
##Fragment添加子Fragment 使用getChildFragmentManager獲取FragmentManager。
final public FragmentManager getChildFragmentManager() { if (mChildFragmentManager == null) { instantiateChildFragmentManager(); if (mState >= RESUMED) { mChildFragmentManager.dispatchResume(); } else if (mState >= STARTED) { mChildFragmentManager.dispatchStart(); } else if (mState >= ACTIVITY_CREATED) { mChildFragmentManager.dispatchActivityCreated(); } else if (mState >= CREATED) { mChildFragmentManager.dispatchCreate(); } } return mChildFragmentManager; } void instantiateChildFragmentManager() { mChildFragmentManager = new FragmentManagerImpl(); mChildFragmentManager.attachController(mHost, new FragmentContainer() { @Override @Nullable public View onFindViewById(int id) { if (mView == null) { throw new IllegalStateException("Fragment does not have a view"); } return mView.findViewById(id); } @Override public boolean onHasView() { return (mView != null); } }, this); }
管理子Fragment的mChildFragmentManager的mHost與Activity中mHost是同一個對象。調用getChildFragmentManager方法時,也會更新mChildFragmentManager的mCurState狀態和子Fragment的狀態。更新流程與上文所講述的一致。