Android的support v4中的Fragment的一个Bug

问题描述

public class MatchFragment extends BaseFragment {    public static final String TAG = MatchFragment.class.getSimpleName();    private FragmentManager mFragmentManager;    public MatchFragment() {        // Required empty public constructor    }    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,            Bundle savedInstanceState) {        // Inflate the layout for this fragment        View view = inflater.inflate(R.layout.fragment_match, container, false);        mFragmentManager = getChildFragmentManager();        FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();        fragmentTransaction.replace(R.id.root_frame_layout, new MatchingFashionFragment());        fragmentTransaction.commit();        return view;    }}

当这个Fragment对象被嵌入到一个Activity中然后又被其他Fragment取代后，然后这个Fragment对象又被重新放回到Activity中时，在fragmentTransaction.commit();处会报如下的错误

java.lang.IllegalStateException: Activity has been destroyed            at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1365)            at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:595)            at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:574)            at com.jd.wxsq.app.Fragment.MatchFragment.onCreateView(MatchFragment.java:70)            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)            at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)            at android.os.Handler.handleCallback(Handler.java:733)            at android.os.Handler.dispatchMessage(Handler.java:95)            at android.os.Looper.loop(Looper.java:136)            at android.app.ActivityThread.main(ActivityThread.java:5017)            at java.lang.reflect.Method.invokeNative(Native Method)            at java.lang.reflect.Method.invoke(Method.java:515)            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)            at dalvik.system.NativeStart.main(Native Method)

问题原因分析

查看android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1365)处的源码：

    public void enqueueAction(Runnable action, boolean allowStateLoss) {        if (!allowStateLoss) {            checkStateLoss();        }        synchronized (this) {            if (mDestroyed || mActivity == null) {                throw new IllegalStateException("Activity has been destroyed");            }            if (mPendingActions == null) {                mPendingActions = new ArrayList();            }            mPendingActions.add(action);            if (mPendingActions.size() == 1) {                mActivity.mHandler.removeCallbacks(mExecCommit);                mActivity.mHandler.post(mExecCommit);            }        }    }

在第7行，可以看到mActivity为null了，所以可以猜测Fragment被detach后，Fragment的mChildFragmentManager的mActivity变为空了，而Fragment被attach后，mChildFragmentManager的mActivity又没有被正确的赋予Activity的对象，才造成了这个bug

在哪里被赋值成null呢？请看下面的代码
C:\Users\lihuaping\AppData\Local\Android\sdk\android-sdk\extras\android\m2repository\com\android\support\support-v4\19.0.0\support-v4-19.0.0-sources.jar!\android\support\v4\app\FragmentManager.java

    public void dispatchDestroy() {        mDestroyed = true;        execPendingActions();        moveToState(Fragment.INITIALIZING, false);        mActivity = null;        mContainer = null;        mParent = null;    }

所以我们要做的就是，在Fragment被detach时，把mChildFragmentManager置空就可以了，mChildFragmentManager是Fragment的私有成员，如何做到？使用反射就可以做到
在你的Fragment的代码中加入如下的代码：

    @Override    public void onDetach() {        super.onDetach();        try {            Field childFragmentManager =                    Fragment.class.getDeclaredField("mChildFragmentManager");            childFragmentManager.setAccessible(true);            childFragmentManager.set(this, null);        } catch (NoSuchFieldException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }    }

问题描述

问题原因分析

更多相关文章

随机推荐