Question

我有一个包含两个片段的活动应用程序：

包含所有UI的片段;
没有视图的片段，其成员AsyncTask，setRetainInstance设置为true。

目标是在活动被破坏后保持AsyncTask运行，并在应用程序重新聚焦时重用它。

我没有使用setTargetFragment，片段之间的所有通信都是通过MainActivity完成的。

我认为setRetainInstance所做的是阻止重新创建片段并保持完全相同的实例，所以当我在重新创建被破坏的活动时调用findFragmentByTag时，它应该返回相同的保留实例，因为它创建时，但似乎并非如此。

结果是我最终得到了一个在后台继续计数的noUi片段（我可以在调试器中看到这个混蛋），另一个，重新创建了一个没有对我运行的AsyncTask的引用...... < / p>

我做错了什么？

以下是一些代码：

public class MainActivity extends Activity
implements FragmentCounter.Callback, FragmentMainScreen.Callback {

private static final String TAG_MAINFRAGMENT = "TAG_MAINFRAGMENT";
private static final String TAG_COUNTERFRAGMENT = "TAG_COUNTERFRAGMENT";
private FragmentMainScreen mFragmentMain;
private FragmentCounter mFragmentCounter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (savedInstanceState == null) {
        mFragmentMain = FragmentMainScreen.getInstance();
        mFragmentCounter = FragmentCounter.getInstance();
        getFragmentManager().beginTransaction()
            .add(R.id.container, mFragmentMain, TAG_MAINFRAGMENT)
            .add(mFragmentCounter, TAG_COUNTERFRAGMENT)
            .commit();
    } else {
        mFragmentMain = (FragmentMainScreen) getFragmentManager()
            .findFragmentByTag(TAG_MAINFRAGMENT);
 //The fragment that gets returned here is not the same instance as the one
 //I returned with getInstance() above.
        mFragmentCounter = (FragmentCounter) getFragmentManager()
                .findFragmentByTag(TAG_COUNTERFRAGMENT);
    }
}
}

noGui片段：

public class FragmentCounter extends Fragment
implements CounterAsyncTask.Callback, FragmentMainScreen.Callback {

private Callback mListener;

private CounterAsyncTask mCounterTask;

public static FragmentCounter getInstance(){
    return new FragmentCounter();
}

public interface Callback {
    public void onData(int aValue);
}

@Override
public void onAttach(Activity activity){
    super.onAttach(activity);
    if (activity instanceof Callback)
        mListener = (Callback) activity;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRetainInstance(true);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    return null;
}

@Override
public void onValueChanged(int value) {
//In the debugger, I can see this callback beeing called,
//even after my activity gets destroyed.
//The mListener is null since I set it that way in the onDetach to
//prevent memory leaks.
//The new activity has a different instance of this Fragment.
    if (mListener != null)
        mListener.onData(value);
}

@Override
public void startCounting(int from) {
    mCounterTask = new CounterAsyncTask(this);
    mCounterTask.execute(from);
}

@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}
}

AsyncTask：

public class CounterAsyncTask extends AsyncTask<Integer, Integer, Void>{

private int counter;
private Callback mListener;
private static final int SKIP = 5000;

public CounterAsyncTask(Callback listener) {
    mListener = listener;
}

@Override
protected Void doInBackground(Integer...values) {
    if (values != null)
        counter = values[0];
    while(!this.isCancelled()){
        publishProgress(counter+=SKIP);
        try{
            Thread.sleep(SKIP);
        }
        catch(InterruptedException e){
            e.printStackTrace();
        }
    }
    return null;
}

@Override
protected void onProgressUpdate(Integer... values) {
    mListener.onValueChanged(values[0]);
}

public interface Callback{
    public void onValueChanged(int value);
}
}

提前致谢！

Answer 1

我的错误。使用setRetainInstance，片段在配置更改时仅保留。因此片段状态将在屏幕旋转时保持，或者如果活动在后台，则不，如果活动被破坏。

为了达到我想要的结果，我应该使用服务。

在setRetainInstance设置为true的片段上调用findFragmentByTag时，不会返回相同的实例

1 个答案: