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11Communicating with Other Fragments(Fragment之间的通信)
In order to reuse the Fragment UI components, you should build each as a completely self-contained, modular component that defines its own layout and behavior. Once you have defined these reusable Fragments, you can associate them with an Activity and connect them with the application logic to realize the overall composite UI.
Often you will want one Fragment to communicate with another, for example to change the content based on a user event. All Fragment-to-Fragment communication is done through the associated Activity. Two Fragments should never communicate directly.
两个Fragment不能直接的通信,必须通过与之相关的Activity才可以通信。
第一步:Define an Interface
定义一个接口:
To allow a Fragment to communicate up to its Activity, you can define an interface in the Fragment class and implement it within the Activity. The Fragment captures the interface implementation during its onAttach() lifecycle method and can then call the Interface methods in order to communicate with the Activity.
public class HeadlinesFragment extends ListFragment { OnHeadlineSelectedListener mCallback; // Container Activity must implement this interface public interface OnHeadlineSelectedListener { public void onArticleSelected(int position); } @Override public void onAttach(Activity activity) { super.onAttach(activity); // This makes sure that the container activity has implemented // the callback interface. If not, it throws an exception try { mCallback = (OnHeadlineSelectedListener) activity; } catch (ClassCastException e) { throw new ClassCastException(activity.toString() + " must implement OnHeadlineSelectedListener"); } } ... }
Now the fragment can deliver messages to the activity by calling the
onArticleSelected()
method (or other methods in the interface) using the mCallback
instance of the OnHeadlineSelectedListener
interface.@Override public void onListItemClick(ListView l, View v, int position, long id) { // Send the event to the host activity mCallback.onArticleSelected(position); }
第二步:Implement the Interface
In order to receive event callbacks from the fragment, the activity that hosts it must implement the interface defined in the fragment class.
For example, the following activity implements the interface from the above example.
public static class MainActivity extends Activity implements HeadlinesFragment.OnHeadlineSelectedListener{ ... public void onArticleSelected(int position) { // The user selected the headline of an article from the HeadlinesFragment // Do something here to display that article } }第三步:Deliver a Message to a Fragment
传递数据给Fragment:
public static class MainActivity extends Activity implements HeadlinesFragment.OnHeadlineSelectedListener{ ... public void onArticleSelected(int position) { // The user selected the headline of an article from the HeadlinesFragment // Do something here to display that article ArticleFragment articleFrag = (ArticleFragment) getSupportFragmentManager().findFragmentById(R.id.article_fragment); if (articleFrag != null) { // If article frag is available, we're in two-pane layout... // Call a method in the ArticleFragment to update its content articleFrag.updateArticleView(position); } else { // Otherwise, we're in the one-pane layout and must swap frags... // Create fragment and give it an argument for the selected article ArticleFragment newFragment = new ArticleFragment(); Bundle args = new Bundle(); args.putInt(ArticleFragment.ARG_POSITION, position); newFragment.setArguments(args); FragmentTransaction transaction = getSupportFragmentManager().beginTransaction(); // Replace whatever is in the fragment_container view with this fragment, // and add the transaction to the back stack so the user can navigate back transaction.replace(R.id.fragment_container, newFragment); transaction.addToBackStack(null); // Commit the transaction transaction.commit(); } } }
其中一个比较重要的方法是:
newFragment.setArguments(args);
11Communicating with Other Fragments(Fragment之间的通信)