详解fragment(一):从源代码看fragment的生命周期

前面讲了那么多xml，我们缓一下，现在讲从代码角度来看fragment的创建。

我们通常会在FragmentActivity中通过如下方法：

getSupportFragmentManager().beginTransaction().replace(R.id.content, fragment, tag).commit();getSupportFragmentManager().beginTransaction().add(R.id.content, fragment, tag).commit();

来调用新建或者取代一个fragment。那你知道这中间发生了什么事情吗，别急，让我们慢慢看代码。

FragmentActivity.java中有个方法:getSupportFragmentManager

public FragmentManager getSupportFragmentManager() {        return mFragments;    }

这个方法用于获取一个FragmentManager，那么这个mFragments是哪里来的呢，我们搜一下这个类，不难发现他的初始化是这个样子的：

    final FragmentManagerImpl mFragments = new FragmentManagerImpl();

从中我们就可以知道FragmentManager以及FragmentManagerImpl是父子类关系。

在FragmentManagerImpl.java中:

final class FragmentManagerImpl extends FragmentManager

而且不用说也可以看出来，FragmentManagerImpl是FragmentManager的具体实现，然后自然而然的我们能找到代码：

public FragmentTransaction beginTransaction()  {    return new BackStackRecord(this);  }

自然而然的我们要去找到BackStackRecord.java这个类了，代码如下：

public BackStackRecord(FragmentManagerImpl manager) {        mManager = manager;    }

接下来，我们看如何添加一个Fragment到Activity，无非是addFragment方法了，我们到FragmentTransaction中看一下(前面说过的Impl类是具体实现)：

public void addFragment(Fragment paramFragment, boolean paramBoolean)  {    if (this.mAdded == null)      this.mAdded = new ArrayList();    if (DEBUG)      Log.v("FragmentManager", "add: " + paramFragment);    makeActive(paramFragment);    if (!paramFragment.mDetached)    {      this.mAdded.add(paramFragment);      paramFragment.mAdded = true;      paramFragment.mRemoving = false;      if ((paramFragment.mHasMenu) && (paramFragment.mMenuVisible))        this.mNeedMenuInvalidate = true;      if (paramBoolean)        moveToState(paramFragment);    }  }

这里果然是有一个数组ArrayList在管理，ArrayList是啥？是动态数组，这就意味着他是可以动态添加的，不是栈，所以里面的Fragments可以随便获取以及插入。

其中最重要的那句话就是moveToState，其实现代码还是比较多的，我们贴一下看看：

void moveToState(Fragment paramFragment, int paramInt1, int paramInt2, int paramInt3)  {    if ((!paramFragment.mAdded) && (paramInt1 > 1))      paramInt1 = 1;    if ((paramFragment.mRemoving) && (paramInt1 > paramFragment.mState))      paramInt1 = paramFragment.mState;    if (paramFragment.mState < paramInt1)    {      if ((paramFragment.mFromLayout) && (!paramFragment.mInLayout))        return;      if (paramFragment.mAnimatingAway != null)      {        paramFragment.mAnimatingAway = null;        moveToState(paramFragment, paramFragment.mStateAfterAnimating, 0, 0);      }      switch (paramFragment.mState)      {      default:      case 0:      case 1:      case 2:      case 3:      case 4:      }    }    while (true)    {      paramFragment.mState = paramInt1;      break;      if (DEBUG)        Log.v("FragmentManager", "moveto CREATED: " + paramFragment);      if (paramFragment.mSavedFragmentState != null)      {        paramFragment.mSavedViewState = paramFragment.mSavedFragmentState.getSparseParcelableArray("android:view_state");        paramFragment.mTarget = getFragment(paramFragment.mSavedFragmentState, "android:target_state");        if (paramFragment.mTarget != null)          paramFragment.mTargetRequestCode = paramFragment.mSavedFragmentState.getInt("android:target_req_state", 0);      }      paramFragment.mActivity = this.mActivity;      paramFragment.mFragmentManager = this.mActivity.mFragments;      paramFragment.mCalled = false;      paramFragment.onAttach(this.mActivity);      if (!paramFragment.mCalled)        throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onAttach()");        //第一步：attach      this.mActivity.onAttachFragment(paramFragment);      if (!paramFragment.mRetaining)      {        paramFragment.mCalled = false;        //第二步：onCreate        paramFragment.onCreate(paramFragment.mSavedFragmentState);        if (!paramFragment.mCalled)          throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onCreate()");      }      paramFragment.mRetaining = false;      if (paramFragment.mFromLayout)      {      //第三步：onCreateView        paramFragment.mView = paramFragment.onCreateView(paramFragment.getLayoutInflater(paramFragment.mSavedFragmentState), null, paramFragment.mSavedFragmentState);        if (paramFragment.mView == null)          break label570;        paramFragment.mInnerView = paramFragment.mView;        paramFragment.mView = NoSaveStateFrameLayout.wrap(paramFragment.mView);        if (paramFragment.mHidden)          paramFragment.mView.setVisibility(8);        paramFragment.onViewCreated(paramFragment.mView, paramFragment.mSavedFragmentState);      }      while (true)      {        if (paramInt1 <= 1)          break label777;        if (DEBUG)          Log.v("FragmentManager", "moveto ACTIVITY_CREATED: " + paramFragment);        if (paramFragment.mFromLayout)          break;        ViewGroup localViewGroup = null;        if (paramFragment.mContainerId != 0)        {          localViewGroup = (ViewGroup)this.mActivity.findViewById(paramFragment.mContainerId);          if ((localViewGroup == null) && (!paramFragment.mRestored))          {            throw new IllegalArgumentException("No view found for id 0x" + Integer.toHexString(paramFragment.mContainerId) + " for fragment " + paramFragment);            label570: paramFragment.mInnerView = null;            continue;          }        }        paramFragment.mContainer = localViewGroup;        paramFragment.mView = paramFragment.onCreateView(paramFragment.getLayoutInflater(paramFragment.mSavedFragmentState), localViewGroup, paramFragment.mSavedFragmentState);        if (paramFragment.mView == null)          break label753;        paramFragment.mInnerView = paramFragment.mView;        paramFragment.mView = NoSaveStateFrameLayout.wrap(paramFragment.mView);        if (localViewGroup != null)        {          Animation localAnimation2 = loadAnimation(paramFragment, paramInt2, true, paramInt3);          if (localAnimation2 != null)            paramFragment.mView.startAnimation(localAnimation2);          localViewGroup.addView(paramFragment.mView);        }        if (paramFragment.mHidden)          paramFragment.mView.setVisibility(8);        paramFragment.onViewCreated(paramFragment.mView, paramFragment.mSavedFragmentState);      }      while (true)      {        paramFragment.mCalled = false;        //第四步：onActivityCreated        paramFragment.onActivityCreated(paramFragment.mSavedFragmentState);        if (paramFragment.mCalled)          break;        throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onActivityCreated()");        label753: paramFragment.mInnerView = null;      }      if (paramFragment.mView != null)        paramFragment.restoreViewState();      paramFragment.mSavedFragmentState = null;      label777: if (paramInt1 > 3)      {        if (DEBUG)          Log.v("FragmentManager", "moveto STARTED: " + paramFragment);        paramFragment.mCalled = false;        paramFragment.performStart();        if (!paramFragment.mCalled)          throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onStart()");      }      if (paramInt1 <= 4)        continue;      if (DEBUG)        Log.v("FragmentManager", "moveto RESUMED: " + paramFragment);      paramFragment.mCalled = false;      paramFragment.mResumed = true;      //第五步：onResume      paramFragment.onResume();      if (!paramFragment.mCalled)        throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onResume()");      paramFragment.mSavedFragmentState = null;      paramFragment.mSavedViewState = null;      continue;      if (paramFragment.mState <= paramInt1)        continue;      switch (paramFragment.mState)      {      default:        break;      case 1:      case 5:      case 4:      case 3:      case 2:        while (paramInt1 < 1)        {          if ((this.mDestroyed) && (paramFragment.mAnimatingAway != null))          {            View localView = paramFragment.mAnimatingAway;            paramFragment.mAnimatingAway = null;            localView.clearAnimation();          }          if (paramFragment.mAnimatingAway == null)            break label1519;          paramFragment.mStateAfterAnimating = paramInt1;          paramInt1 = 1;          break;          if (paramInt1 < 5)          {            if (DEBUG)              Log.v("FragmentManager", "movefrom RESUMED: " + paramFragment);            paramFragment.mCalled = false;            //第六步：onPause            paramFragment.onPause();            if (!paramFragment.mCalled)              throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onPause()");            paramFragment.mResumed = false;          }          if (paramInt1 < 4)          {            if (DEBUG)              Log.v("FragmentManager", "movefrom STARTED: " + paramFragment);            paramFragment.mCalled = false;            paramFragment.performStop();            if (!paramFragment.mCalled)              throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onStop()");          }          if (paramInt1 < 3)          {            if (DEBUG)              Log.v("FragmentManager", "movefrom STOPPED: " + paramFragment);            paramFragment.performReallyStop();          }          if (paramInt1 >= 2)            continue;          if (DEBUG)            Log.v("FragmentManager", "movefrom ACTIVITY_CREATED: " + paramFragment);          if ((paramFragment.mView != null) && (!this.mActivity.isFinishing()) && (paramFragment.mSavedViewState == null))            saveFragmentViewState(paramFragment);          paramFragment.mCalled = false;          paramFragment.performDestroyView();          if (!paramFragment.mCalled)            throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onDestroyView()");          if ((paramFragment.mView != null) && (paramFragment.mContainer != null))          {            Animation localAnimation1 = null;            if ((this.mCurState > 0) && (!this.mDestroyed))              localAnimation1 = loadAnimation(paramFragment, paramInt2, false, paramInt3);            if (localAnimation1 != null)            {              paramFragment.mAnimatingAway = paramFragment.mView;              paramFragment.mStateAfterAnimating = paramInt1;              localAnimation1.setAnimationListener(new Animation.AnimationListener(paramFragment)              {                public void onAnimationEnd(Animation paramAnimation)                {                  if (this.val$fragment.mAnimatingAway != null)                  {                    this.val$fragment.mAnimatingAway = null;                    FragmentManagerImpl.this.moveToState(this.val$fragment, this.val$fragment.mStateAfterAnimating, 0, 0);                  }                }                public void onAnimationRepeat(Animation paramAnimation)                {                }                public void onAnimationStart(Animation paramAnimation)                {                }              });              paramFragment.mView.startAnimation(localAnimation1);            }            paramFragment.mContainer.removeView(paramFragment.mView);          }          paramFragment.mContainer = null;          paramFragment.mView = null;          paramFragment.mInnerView = null;        }        label1519: if (DEBUG)          Log.v("FragmentManager", "movefrom CREATED: " + paramFragment);        if (!paramFragment.mRetaining)        {          paramFragment.mCalled = false;          //第八步：onDestroy          paramFragment.onDestroy();          if (!paramFragment.mCalled)            throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onDestroy()");        }        paramFragment.mCalled = false;        //第九步：onDetach        paramFragment.onDetach();        if (!paramFragment.mCalled)          throw new SuperNotCalledException("Fragment " + paramFragment + " did not call through to super.onDetach()");        if (!paramFragment.mRetaining)        {          makeInactive(paramFragment);          continue;        }        paramFragment.mActivity = null;        paramFragment.mFragmentManager = null;      }    }  }

本来不想贴这部分的代码的，但确实这个比较重要，还是看一下吧。

最后一步肯定是commit了，这个方法是由FragmentTransaction.java类调用的，其实包括前面的addFragment等都是在这个类调用的，可是他是个抽象类，具体的实现还是在Impl类中。我们还是稍微浏览一下这个类吧（只截取了部分）：

public abstract class FragmentTransaction {    public abstract FragmentTransaction add(int containerViewId, Fragment fragment);       public abstract FragmentTransaction add(int containerViewId, Fragment fragment, String tag);       public abstract FragmentTransaction replace(int containerViewId, Fragment fragment);       public abstract FragmentTransaction replace(int containerViewId, Fragment fragment, String tag);       public abstract FragmentTransaction remove(Fragment fragment);       public abstract FragmentTransaction hide(Fragment fragment);            public abstract FragmentTransaction show(Fragment fragment);        public abstract FragmentTransaction detach(Fragment fragment);    public abstract FragmentTransaction attach(Fragment fragment);    public abstract int commit();}

最后看commit的实现，本人目前还没找到，求告诉！