Fragment间的通信
在网上看到的一篇文章,总结的很好
为了重用Fragment的UI组件,创建的每个Fragment都应该是自包含的、有它自己的布局和行为的模块化组件。一旦你定义了这些可重用的Fragment,你就可以把它们跟一个Activity关联,并把它们跟应用程序的逻辑相连来实现全部的组合式UI。
现实中我们经常想要一个Fragment跟另一个Fragment进行通信,例如,要基于一个用户事件来改变内容。所有的Fragment间的通信都是通过跟关联的Activity来完成的。另个Fragment不应该直接通信。也就是说Fragment间不直接通信,通过Activity转一下,按java常规,转一下多是使用Interface实现的。
定义Interface
为了让Fragment跟它的Activity通信,你可以在Fragment类中定义一个接口,并在它所属的Activity中实现该接口。Fragment在它的onAttach()方法执行期间捕获该接口的实现,然后就可以调用接口方法,以便跟Activity通信。
以下是Fragment跟Activity通信的示例:
- 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");
- }
- }
- ...
- }
现在,这个Fragment就可以通过调用OnHealdlineSelectedListener接口实例mCallback的onArticleSelected()方法(或其他的接口中的方法)给Activity发送消息。
例如,在Fragment中的下列方法会用户点击列表项时被调用。该Fragment使用回调接口把该事件发送给它的父Activity。
- @Override
- public void onListItemClick(ListView l, View v, int position, long id) {
- // Send the event to the host activity
- mCallback.onArticleSelected(position);
- }
实现Interface
为了从Fragment中接收事件回调,包含Fragment的Activity必须实现Fragment类中定义的接口。
例如,下面Activity实现了上面示例中定义的接口:
- 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
- }
- }
把消息传递给另一个Fragment
通过使用findFragmentById()方法捕获Fragment实例,宿主Activity可以把消息发送给该Fragment,然后直接调用该Fragment的公共方法。
例如,上面的示例,Activty通过Interface的实现方法,传递数据到另一个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();
- }
- }
- }
Fragment中使用左右滑动菜单 中应用到了Fragment间的通信
参考:http://developer.android.com/training/basics/fragments/communicating.html
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