片段应该如何获得有关异步任务结果的通知？

Question

我有一个使用片段的活动。这些片段可能会根据用户的交互来来去去。其中许多片段将作业启动到 IntentService，从而以这种方式异步运行。 IntentService 应如何报告这些作业的结果？

启动作业的片段可能不存在。如果作业完成并且起始片段当前处于活动状态，那么它应该收到有关此情况的通知，并采取相应的行动。如果不是，则无需执行任何操作。

我考虑过使用广播意图和 BroadcastReceiver 组件，但片段无法注册接收器，只能注册活动。

您会建议什么解决方案？

Answer 1

我在 IOSched 应用（适用于 Android 的 Google I/O 应用）中注意到同样的问题。

他们创建了 DetachableResultReceiver，其中扩展 SDK 类 ResultReciever。

他们很容易 在片段中使用它。

接收者：

/**
 * Proxy {@link ResultReceiver} that offers a listener interface that can be
 * detached. Useful for when sending callbacks to a {@link Service} where a
 * listening {@link Activity} can be swapped out during configuration changes.
 */
public class DetachableResultReceiver extends ResultReceiver {
    private static final String TAG = "DetachableResultReceiver";

    private Receiver mReceiver;

    public DetachableResultReceiver(Handler handler) {
        super(handler);
    }

    public void clearReceiver() {
        mReceiver = null;
    }

    public void setReceiver(Receiver receiver) {
        mReceiver = receiver;
    }

    public interface Receiver {
        public void onReceiveResult(int resultCode, Bundle resultData);
    }

    @Override
    protected void onReceiveResult(int resultCode, Bundle resultData) {
        if (mReceiver != null) {
            mReceiver.onReceiveResult(resultCode, resultData);
        } else {
            Log.w(TAG, "Dropping result on floor for code " + resultCode + ": "
                    + resultData.toString());
        }
    }
}

活动和片段：

public class HomeActivity extends BaseActivity {
    private static final String TAG = "HomeActivity";

    private SyncStatusUpdaterFragment mSyncStatusUpdaterFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //...

        mTagStreamFragment = (TagStreamFragment) fm.findFragmentById(R.id.fragment_tag_stream);

        mSyncStatusUpdaterFragment = (SyncStatusUpdaterFragment) fm
                .findFragmentByTag(SyncStatusUpdaterFragment.TAG);
        if (mSyncStatusUpdaterFragment == null) {
            mSyncStatusUpdaterFragment = new SyncStatusUpdaterFragment();
            fm.beginTransaction().add(mSyncStatusUpdaterFragment,
                    SyncStatusUpdaterFragment.TAG).commit();

            triggerRefresh();
        }
    }

    private void triggerRefresh() {
        final Intent intent = new Intent(Intent.ACTION_SYNC, null, this, SyncService.class);
        intent.putExtra(SyncService.EXTRA_STATUS_RECEIVER, mSyncStatusUpdaterFragment.mReceiver);
        startService(intent);

        if (mTagStreamFragment != null) {
            mTagStreamFragment.refresh();
        }
    }

    /**
     * A non-UI fragment, retained across configuration changes, that updates its activity's UI
     * when sync status changes.
     */
    public static class SyncStatusUpdaterFragment extends Fragment
            implements DetachableResultReceiver.Receiver {
        public static final String TAG = SyncStatusUpdaterFragment.class.getName();

        private boolean mSyncing = false;
        private DetachableResultReceiver mReceiver;

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setRetainInstance(true);
            mReceiver = new DetachableResultReceiver(new Handler());
            mReceiver.setReceiver(this);
        }

        /** {@inheritDoc} */
        public void onReceiveResult(int resultCode, Bundle resultData) {
            HomeActivity activity = (HomeActivity) getActivity();
            if (activity == null) {
                return;
            }

            switch (resultCode) {
                case SyncService.STATUS_RUNNING: {
                    mSyncing = true;
                    break;
                }
                //...
            }

            activity.updateRefreshStatus(mSyncing);
        }

        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            ((HomeActivity) getActivity()).updateRefreshStatus(mSyncing);
        }
    }
}