支持 FragmentPagerAdapter 保存对旧片段的引用

我已将问题缩小为 FragmentManager 保留旧片段实例的问题，以及我的 viewpager 与 FragmentManager 不同步的问题.请参阅此问题:http://code.google.com/p/android/issues/detail?id=19211#makechanges.我仍然不知道如何解决这个问题.有什么建议吗?

I have narrowed my problem down to being a problem with the FragmentManager retaining instances of old fragments and my viewpager being out of sync with my FragmentManager. See this issue: http://code.google.com/p/android/issues/detail?id=19211#makechanges. I still have no clue how to solve this. Any suggestions?

我已经尝试调试了很长时间，任何帮助将不胜感激.我正在使用 FragmentPagerAdapter，它接受像这样的片段列表:

I have tried to debug this for a long time and any help would be greatly appreciated. I am using a FragmentPagerAdapter which accepts a list of fragments like so:

List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this, Fragment1.class.getName())); 
...
new PagerAdapter(getSupportFragmentManager(), fragments);

实施是标准的.我正在为 Fragment 使用 ActionBarSherlock 和 v4 可计算性库.

The implementation is standard. I am using ActionBarSherlock and v4 computability library for Fragments.

我的问题是，在离开应用程序并打开其他几个应用程序并返回后，片段失去了对 FragmentActivity 的引用(即 getActivity() == null).我不明白为什么会这样.我试图手动设置 setRetainInstance(true); 但这没有帮助.我认为当我的 FragmentActivity 被破坏时会发生这种情况，但是如果我在收到日志消息之前打开应用程序，这种情况仍然会发生.有什么想法吗?

My problem is that after leaving the app and opening several other applications and coming back, the fragments lose their reference back to the FragmentActivity (ie. getActivity() == null). I can not figure out why this is happening. I tried to manually set setRetainInstance(true); but this does not help. I figured that this happens when my FragmentActivity gets destroyed, however this still happens if I open the app before I get the log message. Are there any ideas?

@Override
protected void onDestroy(){
    Log.w(TAG, "DESTROYDESTROYDESTROYDESTROYDESTROYDESTROYDESTROY");
    super.onDestroy();
}

适配器:

public class PagerAdapter extends FragmentPagerAdapter {
    private List<Fragment> fragments;

    public PagerAdapter(FragmentManager fm, List<Fragment> fragments) {
        super(fm);

        this.fragments = fragments;

    }

    @Override
    public Fragment getItem(int position) {

        return this.fragments.get(position);

    }

    @Override
    public int getCount() {

        return this.fragments.size();

    }

}

我的一个 Fragments 被剥离了，但我将所有被剥离的片段都注释掉了，但它仍然不起作用.

One of my Fragments stripped but I commented everything out that's stripped and it still doesn't work.

public class MyFragment extends Fragment implements MyFragmentInterface, OnScrollListener {
...

@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    handler = new Handler();    
    setHasOptionsMenu(true);
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    Log.w(TAG,"ATTACHATTACHATTACHATTACHATTACH");
    context = activity;
    if(context== null){
        Log.e("IS NULL", "NULLNULLNULLNULLNULLNULLNULLNULLNULLNULLNULL");
    }else{
        Log.d("IS NOT NULL", "NOTNOTNOTNOTNOTNOTNOTNOT");
    }

}

@Override
public void onActivityCreated(Bundle savedState) {
    super.onActivityCreated(savedState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.my_fragment,container, false);

    return v;
}


@Override
public void onResume(){
    super.onResume();
}

private void callService(){
    // do not call another service is already running
    if(startLoad || !canSet) return;
    // set flag
    startLoad = true;
    canSet = false;
    // show the bottom spinner
    addFooter();
    Intent intent = new Intent(context, MyService.class);
    intent.putExtra(MyService.STATUS_RECEIVER, resultReceiver);
    context.startService(intent);
}

private ResultReceiver resultReceiver = new ResultReceiver(null) {
    @Override
    protected void onReceiveResult(int resultCode, final Bundle resultData) {
        boolean isSet = false;
        if(resultData!=null)
        if(resultData.containsKey(MyService.STATUS_FINISHED_GET)){
            if(resultData.getBoolean(MyService.STATUS_FINISHED_GET)){
                removeFooter();
                startLoad = false;
                isSet = true;
            }
        }

        switch(resultCode){
        case MyService.STATUS_FINISHED: 
            stopSpinning();
            break;
        case SyncService.STATUS_RUNNING:
            break;
        case SyncService.STATUS_ERROR:
            break;
        }
    }
};

public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    menu.clear();
    inflater.inflate(R.menu.activity, menu);
}

@Override
public void onPause(){
    super.onPause();
}

public void onScroll(AbsListView arg0, int firstVisible, int visibleCount, int totalCount) {
    boolean loadMore = /* maybe add a padding */
        firstVisible + visibleCount >= totalCount;
        
    boolean away = firstVisible+ visibleCount <= totalCount - visibleCount;
        
    if(away){
        // startLoad can now be set again
        canSet = true;
    }
        
    if(loadMore) 
        
}

public void onScrollStateChanged(AbsListView arg0, int state) {
    switch(state){
    case OnScrollListener.SCROLL_STATE_FLING: 
        adapter.setLoad(false); 
        lastState = OnScrollListener.SCROLL_STATE_FLING;
        break;
    case OnScrollListener.SCROLL_STATE_IDLE: 
        adapter.setLoad(true);
        if(lastState == SCROLL_STATE_FLING){
            // load the images on screen
        }
        
        lastState = OnScrollListener.SCROLL_STATE_IDLE;
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        adapter.setLoad(true);
        if(lastState == SCROLL_STATE_FLING){
            // load the images on screen
        }
        
        lastState = OnScrollListener.SCROLL_STATE_TOUCH_SCROLL;
        break;
    }
}

@Override
public void onDetach(){
    super.onDetach();
    if(this.adapter!=null)
        this.adapter.clearContext();
    
    Log.w(TAG, "DETACHEDDETACHEDDETACHEDDETACHEDDETACHEDDETACHED");
}

public void update(final int id, String name) {
    if(name!=null){
        getActivity().getSupportActionBar().setTitle(name);
    }
    
}

}

当用户与不同的片段交互并且 getActivity 返回 null 时，将调用更新方法.这是另一个片段调用的方法:

The update method is called when a user interacts with a different fragment and the getActivity is returning null. Here is the method the other fragment is calling:

((MyFragment) pagerAdapter.getItem(1)).update(id, name);

我相信当应用程序被销毁然后再次创建时，而不是仅仅将应用程序启动到默认片段，应用程序会启动，然后 viewpager 导航到最后一个已知页面.这看起来很奇怪，应用程序不应该只是加载到默认片段吗?

I believe that when the app is destroyed then created again instead of just starting the app up to the default fragment the app starts up and then viewpager navigates to the last known page. This seems strange, shouldn't the app just load to the default fragment?