原文地址：

-------------------------------------------------------------------------------------------------------------------------

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.

为了重用Fragment UI部件，你应该每一个建成完全独立的、模块化的部件，定义了它自己的布局和行为。一旦你已经定义了这些可重用的Fragments，你可以将它们与一个Activity相关联，并将它们和应用逻辑相连接来实现整体复合的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.

一旦你想要让一个Fragment和另一个进行交流，例如基于用户时间改变内容。所有的Fragment-to-Fragment交互通过相关联的Activity来完成。两个Fragment永远不应该直接交互。

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.

为了允许一个Fragment和它的Activity进行交互，你可以在Fragment类中定义一个接口，然后在Activity中实现它。Fragment在它的onAttach()生命周期方法中捕捉这个接口的实现，并且之后可以调用接口方法来达到和Activity交互的目的。

Here is an example of Fragment to Activity communication:

下面是一个Fragment和Activity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");        }    }        ...}

Now the fragment can deliver messages to the activity by calling the onArticleSelected() method (or other methods in the interface) using themCallback instance of theOnHeadlineSelectedListener interface.

现在，Fragment可以通过调用onArticleSelected()方法（或者其他接口中的方法）、使用OnHeadlineSelectedListener接口的实例mCallback向activity交付信息。

For example, the following method in the fragment is called when the user clicks on a list item. The fragment uses the callback interface to deliver the event to the parent activity.

例如，当用户在一个列表上点击时将调用下面的方法。Fragment使用回调函数接口来向父类activity交付事件。

@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

---

In order to receive event callbacks from the fragment, the activity that hosts it must implement the interface defined in the fragment class.

为了从Fragment中接收事件回调函数，持有它的activity必须实现在Fragment类中定义的接口。

For example, the following activity implements the interface from the above example.

例如，下面的activity实现了上述例子的接口。

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 —— 向一个Fragment交付信息

---

The host activity can deliver messages to a fragment by capturing the instance with, then directly call the fragment's public methods.

主activity可以通过实例、使用向Fragment交付信息，然后直接调用Fragment的公共方法。

For instance, imagine that the activity shown above may contain another fragment that's used to display the item specified by the data returned in the above callback method. In this case, the activity can pass the information received in the callback method to the other fragment that will display the item:

例如，想象上面演示的activity可以包含另一个Fragment来显示上述回调函数返回的数据。在这种情况下，activity可以向另一个显示它们的Fragment传递回调函数中接收的信息。

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();        }    }}