Fragment生命周期

---

Fragment依赖于Activity，生命周期与Activity的类似。
六个状态

static final int INITIALIZING = 0;     // Not yet created.
static final int CREATED = 1;          // Created.
static final int ACTIVITY_CREATED = 2; // activity完成创建
static final int STOPPED = 3;          // created, not started.
static final int STARTED = 4;          //  not resumed.
static final int RESUMED = 5;          // resumed.

FragmentManager#moveToState方法。

void moveToState(Fragment f, int newState, int transit, int 
                    transitionStyle,boolean keepActive) {
    if (f.mState < newState) {
        switch (f.mState) {//创建与初始化
            case Fragment.INITIALIZING:
            case Fragment.CREATED:
            case Fragment.ACTIVITY_CREATED:
            case Fragment.STOPPED:        
            case Fragment.STARTED:
        }
    } else if (f.mState > newState) {
        switch (f.mState) {//暂停或销毁
            case Fragment.RESUMED:
            case Fragment.STARTED:
            case Fragment.STOPPED:
            case Fragment.ACTIVITY_CREATED:
            case Fragment.CREATED:  
        }
    }
}

比较Fragment当前mState和新newState状态。

• 若新newState大于mState，Fragment创建与初始化。
• 若新newState小于mState，Fragment暂停或销毁。
• 状态转换过程触发一系列生命周期方法。

启动生命周期

Fragment创建启动生命周期。 Fragment创建启动生命周期.jpg

1，INITIALIZING->CREATED

Fragment还未初始化。
Fragment#onAttach方法。

public void onAttach(Context context) {
    mCalled = true;
    final Activity hostActivity = 
                    mHost == null ? null : mHost.getActivity();
    if (hostActivity != null) {
        mCalled = false;
        onAttach(hostActivity);
    }
}

mHost是FragmentHostCallback类型，在onAttach执行前赋值。获取依附的Activity，触发Fragment#onAttach方法。
Fragment#performCreate方法。

void performCreate(Bundle savedInstanceState) {
    ...
    mState = CREATED;
    mCalled = false;
    onCreate(savedInstanceState);
    if (!mCalled) {
        throw new SuperNotCalledException("Fragment " + this
                    + " did not call through to super.onCreate()");
    }
}

触发onCreate，在onCreate会判断恢复savedInstanceState。
Fragment#onCreate方法。

public void onCreate(@Nullable Bundle savedInstanceState) {
    mCalled = true;
    restoreChildFragmentState(savedInstanceState);
    if (mChildFragmentManager != null
                && !mChildFragmentManager.isStateAtLeast(Fragment.CREATED)) {
        mChildFragmentManager.dispatchCreate();
    }
}

2，CREATED->ACTIVITY_CREATED

Fragment已经完成了初始化，这一步完成视图创建。

依次触发：onCreateView，onViewCreated，onActivityCreated

Fragment#performCreateView方法

View performCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
    ..
    return onCreateView(inflater, container, savedInstanceState);
}

默认onCreateView返回空，需重写onCreateView方法，创建视图，赋值给f.mView。
Fragment#onViewCreated方法是空方法，子类中可重写，初始化控件资源。
Fragment#performActivityCreated方法。

void performActivityCreated(Bundle savedInstanceState) {
    ..
    mState = ACTIVITY_CREATED;
    mCalled = false;
    onActivityCreated(savedInstanceState);
    if (!mCalled) {
        throw new SuperNotCalledException("Fragment " + this
                    + " did not call through to super.onActivityCreated()");
    }
    ...
}

触发onActivityCreated，将mCalled设置为true，子类重写该方法。

public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    mCalled = true;
}

3，ACTIVITY_CREATED->STOPPED

activity完成创建。

case Fragment.ACTIVITY_CREATED:
    if (newState > Fragment.ACTIVITY_CREATED) {
        f.mState = Fragment.STOPPED;
    }

4，STOPPED->STARTED

完全创建完成，还未start。

case Fragment.STOPPED:
if (newState > Fragment.STOPPED) {
    f.performStart();
}

Fragment开始可见。
Fragment#performStart方法。

void performStart() {
    ...
    mState = STARTED;
    mCalled = false;
    onStart();
    if (!mCalled) {//抛出异常
    }
    ...
}

触发onStart，将mCalled设置为true，子类可重写该方法。

5，STARTED->RESUMED

case Fragment.STARTED:
if (newState > Fragment.STARTED) {
    f.performResume();
    f.mSavedFragmentState = null;
    f.mSavedViewState = null;
}

活动状态，可交互。
Fragment#performResume方法。

void performResume() {
    ...
    mState = RESUMED;
    mCalled = false;
    onResume();
    if (!mCalled) {//抛出异常
    }
    ..
}

触发onResume方法，将mCalled设置为true，子类可重写该方法。

RESUMED状态

活动状态。

---

销毁生命周期

Fragment销毁生命周期。 Fragment销毁生命周期.jpg

1，RESUMED->STARTED

case Fragment.RESUMED:
    if (newState < Fragment.RESUMED) {
        f.performPause();
    }

使Fragment处于暂停状态，可见，无法交互。
Fragment#performPause方法。

void performPause() {
    ...
    mState = STARTED;
    mCalled = false;
    onPause();
    if (!mCalled) {//抛出异常
    }
}

触发Fragment#onPause，将mCalled设置为true，子类可重写该方法。

2，STARTED->STOPPED

case Fragment.STARTED:
    if (newState < Fragment.STARTED) {
        f.performStop();
    }

使Fragment不可见。
Fragment#performStop方法

void performStop() {
    ...
    mState = STOPPED;
    mCalled = false;
    onStop();
    if (!mCalled) {//抛出异常
    }
}

触发Fragment#onStop方法，将mCalled设置为true，子类可重写该方法。

3，STOPPED->ACTIVITY_CREATED

case Fragment.STOPPED:
    if (newState < Fragment.STOPPED) {
        f.performReallyStop();
    }

4，,ACTIVITY_CREATED->CREATED

Fragment#performDestroyView方法。

void performDestroyView() {
    ...
    mState = CREATED;
    mCalled = false;
    onDestroyView();
    ....
}

销毁与Fragment有关的视图，但未与Activity解除绑定。
触发Fragment#onDestroyView方法。

5，CREATED->INITIALIZING

Fragment#performDestroy方法。

void performDestroy() {
    ....
    mState = INITIALIZING;
    mCalled = false;
    onDestroy();
    ....
}

销毁Fragment，触发onDestory方法。
Fragment#performDetach方法。
解除与Activity绑定，触发onDetach方法。

生命周期方法总结
onAttach，onCreate，onCreateView，onViewCreated，onActivityCreated，onStart，onResume

onPause，onStop，onDestoryView，onDestory，onDetach。

---

任重而道远