Communicating with Other Fragments

  次阅读 来源:互联网(转载协议) 2015-09-29 10:59 我要评论(0)

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.

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.

Define an Interface

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.

Here is an example of Fragment to Activity communication:

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 the mCallback instance of the OnHeadlineSelectedListener interface.

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.

@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

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

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

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

}

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