原文自:http://android.eoe.cn/topic/ui
Communicating with Other Fragments
为了重用Fragment UI组件,你应该将Fragment建立成完全独立,模块化并且定义了自己布局和行为的组件。一旦你定义了这些可重用的Fragment,你可以通过activity,应用程序逻辑使它们关联,交互以组成一个整体复合型UI。
通常情况下,你希望一个Fragment可以与另一个交互,比如基于用户事件去修改内容。所有Fragment到Fragment的交互都是通过相关联的activity来做的。两个fragment应该从不直接交互。
定义一个接口 Define an Interface
为了允许Fragment与它的activity交互,你可以在fragment类中定义一个接口并且在activity中实现它。fragment可以在生命周期中的onAttach()方法获取接口的实现并调用接口的方法与activity交互。
以下是fragment到activity的交互例子:
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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");
}
}
...
}
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现在fragment可以使用OnHeadlineSelectedListener的实例mCallback调用onArticleSelected()方法(或者其他接口内的方法)提供信息给activity了。
例如,当用户点击list item(list子项)时就会调用下面在fragment的方法。fragment使用回调接口提供事件到父的activity。
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@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Send the event to the host activity
mCallback.onArticleSelected(position);
}
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实现接口 Implement the Interface
为了接收来自fragment的事件回调,包含fragment的activity(你需要用来与fragment交互的activity)必须实现定义在fragment类中的接口。
例如:下面这个activity就实现了上一例子中的接口:
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public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
...
public void onArticleSelected(Uri articleUri) {
// The user selected the headline of an article from the HeadlinesFragment
// Do something here to display that article
}
}
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Deliver a Message to a Fragment
宿主activity可以使用findFragmentById()方法获取Fragment实例,然后直接调用fragment的公共方法提供信息给fragment。
例如,假设在上面显示的那个activity中可能包含另外一个fragment,并且用来显示由上面那个回调方法返回的数据指定的项目。在这个案例中,这个activity可以从回调函数中获得信息并且传递给其他显示项目的fragment:
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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();
}
}
}
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