Fragment状态变化，触发了哪些方法

1、追踪FragmentManager对Fragment操做涉及到方法

getSupportFragmentManager().beginTransaction().remove(Fragment fragment).commit()

BackStackRecord remove(Fragment fragment)
BackStackRecord.commit() // 开始
BackStackRecord.commitInternal(boolean allowStateLoss)

FragmentManagerImpl.enqueueAction(OpGenerator action, boolean allowStateLoss)
// 涉及到Handler的延时处理
FragmentManager.scheduleCommit() {
        synchronized (this) {
            boolean postponeReady =
                    mPostponedTransactions != null && !mPostponedTransactions.isEmpty();
            boolean pendingReady = mPendingActions != null && mPendingActions.size() == 1;
            if (postponeReady || pendingReady) {
                mHost.getHandler().removeCallbacks(mExecCommit);
                mHost.getHandler().post(mExecCommit);
            }
        }
}

handler将进一步操做Runnable

Runnable mExecCommit = new Runnable() {
        @Override
        public void run() {
            execPendingActions();
        }
    };

FragmentManager.execPendingActions()
FragmentManager.doPendingDeferredStart()
FragmentManager.startPendingDeferredFragments()
FragmentManager.performPendingDeferredStart(Fragment f)
FragmentManager.moveToState(Fragment f, int newState, int transit, int transitionStyle, boolean keepActive){
   case Fragment.ACTIVITY_CREATED:
       onDestroyView();
       mContainer.removeView(f.mView)
       f.view.dispatchDetachedFromWindow();
       f.mContainer = null;
       f.mView = null;
   case Fragment.CREATED:
       f.performDestroy();
       f.performDetach();
       makeInactive(f);
       f.mHost = null;
}

moveToState 是状态变化的核心方法，须要进一步查看源码

2、FragmentManager.moveToState解析

FragmentActivity维护着FragmentManager一个实例，而FragmentManager管理者Fragment的各个状态， 查看FragmentManagerImpl源码中

FragmentManagerImpl{
 int mCurState = Fragment.INITIALIZING; //初始化状态
}

Fragment{
    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.
}

mCurState就是当前FragmentManager的状态,mCurState只有一个方法中对其有赋值操做moveToState(int newState, boolean always)而这个方法调用处以下：

public void dispatchCreate() {
        mStateSaved = false;
        mStopped = false;
        dispatchStateChange(Fragment.CREATED);
    }

    public void dispatchActivityCreated() {
        mStateSaved = false;
        mStopped = false;
        dispatchStateChange(Fragment.ACTIVITY_CREATED);
    }

    public void dispatchStart() {
        mStateSaved = false;
        mStopped = false;
        dispatchStateChange(Fragment.STARTED);
    }

    public void dispatchResume() {
        mStateSaved = false;
        mStopped = false;
        dispatchStateChange(Fragment.RESUMED);
    }

    public void dispatchPause() {
        dispatchStateChange(Fragment.STARTED);
    }

    public void dispatchStop() {
        mStopped = true;
        dispatchStateChange(Fragment.STOPPED);
    }

方法对应着状态值的调整，看命名好像和Activity的生命周期对于，咱们再对照FragmentActivity的源码

public void dispatchCreate() {
        mHost.mFragmentManager.dispatchCreate();
    }

    public void dispatchActivityCreated() {
        mHost.mFragmentManager.dispatchActivityCreated();
    }

    public void dispatchStart() {
        mHost.mFragmentManager.dispatchStart();
    }

    public void dispatchResume() {
        mHost.mFragmentManager.dispatchResume();
    }

    public void dispatchPause() {
        mHost.mFragmentManager.dispatchPause();
    }

    public void dispatchStop() {
        mHost.mFragmentManager.dispatchStop();
    }

果真是由Activity来触发FragmentManager的状态变化 接下来详细看下FragmentManager.moveToState(Fragment f, int newState, int transit, int transitionStyle, boolean keepActive)方法 简化以下：

if (f.mState < newState) {
            switch (f.mState) {
                case Fragment.INITIALIZING:
                    //some code
                case Fragment.CREATED:
                    if (newState > Fragment.CREATED) {
                        //some code
                    }
                case Fragment.ACTIVITY_CREATED:
                case Fragment.STOPPED:
                    if (newState > Fragment.STOPPED) {
                        //some code
                    }
                case Fragment.STARTED:
                    if (newState > Fragment.STARTED) {
                        //some code
                    }
            }
        } else if (f.mState > newState) {
            switch (f.mState) {
                case Fragment.RESUMED:
                    if (newState < Fragment.RESUMED) {
                        //some code
                    }
                case Fragment.STARTED:
                    if (newState < Fragment.STARTED) {
                        //some code
                    }
                case Fragment.STOPPED:
                    if (newState < Fragment.STOPPED) {
                        //some code
                    }
                case Fragment.ACTIVITY_CREATED:
                    if (newState < Fragment.ACTIVITY_CREATED) {
                        //some code
                    }
                case Fragment.CREATED:
                    if (newState < Fragment.CREATED) {
                        //some code
                    }
            }
        }
        f.mState = newState;

在每一个case中都没有break，则会顺序执行，主要是fragment状态和FragmentManager的状态进行了对比，

• 1）fragment状态小于FragmentManager的状态，相似Activity已完成初始化，用户点击操做，开始addFragment，则开始顺序执行初始化Fragment的状态；
• 2）fragment状态大于FragmentManager的状态，相似Activity已完成初始化，用户点击操做，开始removeFragment，则开始删除Fragment 最终Fragment状态和FragmentManager的状态同步