【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！