Android中两个类让你再也不用实现onActivityResult()

前言

当我们知道fragment仅仅可以收到自己请求的回调后，我们就可以用它来解耦activity中onActivityResult的逻辑了。一般情况下，如果一个activity中多个回调结果的话，onActivityResult()中会有各种case判断，并且这种设计也打断了流式写法。那么我们索性建立一个无UI的fragment做精准的接收器，这样就可以再也不写onActivityResult()了。

Fragment：

public class onActResultEventDispatcherFragment extends Fragment {

 public static final String TAG = "on_act_result_event_dispatcher";

 private SparseArray mCallbacks = new SparseArray<>();

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

 public void startForResult(Intent intent, ActResultRequest.Callback callback) {
  mCallbacks.put(callback.hashCode(), callback);
  startActivityForResult(intent, callback.hashCode());
 }

 @Override
 public void onActivityResult(int requestCode, int resultCode, Intent data) {
  super.onActivityResult(requestCode, resultCode, data);

  ActResultRequest.Callback callback = mCallbacks.get(requestCode);
  mCallbacks.remove(requestCode);

  if (callback != null) {
   callback.onActivityResult(resultCode, data);
  }
 }
}

请求封装类：

public class ActResultRequest {

 private onActResultEventDispatcherFragment fragment;

 public ActResultRequest(Activity activity) {
  fragment = getEventDispatchFragment(activity);
 }

 private onActResultEventDispatcherFragment getEventDispatchFragment(Activity activity) {
  final FragmentManager fragmentManager = activity.getFragmentManager();

  onActResultEventDispatcherFragment fragment = findEventDispatchFragment(fragmentManager);
  if (fragment == null) {
   fragment = new onActResultEventDispatcherFragment();
   fragmentManager
     .beginTransaction()
     .add(fragment, OnActResultEventDispatcherFragment.TAG)
     .commitAllowingStateLoss();
   fragmentManager.executePendingTransactions();
  }
  return fragment;
 }

 private onActResultEventDispatcherFragment findEventDispatchFragment(FragmentManager manager) {
  return (OnActResultEventDispatcherFragment) manager.findFragmentByTag(OnActResultEventDispatcherFragment.TAG);
 }

 public void startForResult(Intent intent, Callback callback) {
  fragment.startForResult(intent, callback);
 }

 public interface Callback {

  void onActivityResult(int resultCode, Intent data);
 }
}

发送请求和监听请求的代码：

Intent intent = new Intent(this, SecondActivity.class);

request.startForResult(intent, new ActResultRequest.Callback() {
 @Override
 public void onActivityResult(int resultCode, Intent data) {
  Toast.makeText(MainActivity.this, "" + resultCode, Toast.LENGTH_SHORT).show();
 }
});

题外话：

最新的support包已经解决了fragment嵌套时里层的fragment收不到结果的问题，请及时更新依赖。

总结

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