【Android Training - 03】使用Fragments建立动态的UI [ Lesson 4 - Fragment之间的通信 ]

为了重用fragment的UI组件，你必须为每个fragment建立自己的container，模块化自己的layout与行为。一旦你定义了那些可重用的fragment，你可以使用activity与他们建立联系，对那些UI组件做组合动作等。

通常，你也会想要fragment-s之间能够交流。例如，基于用户事件来改变内容。所有的Fragment-to-Fragment之间的交互都是基于activity进行操作的。两个fragment之间没有办法直接交互。

Define an Interface [定义接口]

为了允许fragment与activity进行交互，你可以在fragment中定义一个interface，然后在activity中去implement它。Fragment在它的onAttach()方法里面捕获接口的实现，然后call接口的方法来与activity进行交互。

下面是一个fragment与activity进行交互的例子：

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");
}
}

...
}

那么现在，fragment可以通过

onArticleSelected()

 传递messages给activity。这个方法去使用OnHeadlineSelectedListener接口的

mCallback

例如：下面在fragment中的方法会在用户点击listitem的时候被call到。Fragment使用这个callback接口来传递事件给父activity。

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Send the event to the host activity
mCallback.onArticleSelected(position);
}

Implement the Interface [实现接口]

为了接受到fragment返回事件的callback，包含那个fragment的activity必须实现定义在fragment中的接口。

例如：下面的activity实现了上面例子中的接口。

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
}
}

Deliver a Message to a Fragment [传递msg给fragment]

宿主activity可以通过

findFragmentById()

捕获到fragment实例，然后call
fragment的public方法来传递msg给fragment。

如下演示了使用另外一个fragment来显示从上面例子的callback中获取到的内容。

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();
}
}
}

学习自：https://developer.android.com/training/basics/fragments/communicating.html，欢迎一起交流！

转载请注明出自：http://blog.csdn.net/kesenhoo，谢谢！