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.html
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.android
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.app
Here is an example of Fragment to Activity communication:ide
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.模塊化
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.佈局
@Override public void onListItemClick(ListView l, View v, int position, long id) { // Send the event to the host activity mCallback.onArticleSelected(position); }
In order to receive event callbacks from the fragment, the activity that hosts it must implement the interface defined in the fragment class.ui
For example, the following activity implements the interface from the above example.this
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 } }
The host activity can deliver messages to a fragment by capturing the Fragment instance withfindFragmentById(), then directly call the fragment's public methods.spa
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:翻譯
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(); } } }
爲了能重用UI部件，你應該自定義每個Fragment的佈局和功能，使他們能成爲徹底獨立的模塊。定義好這些模塊化的Fragment後，就能夠讓他們關聯activity，使他們與application的邏輯結合起來，實現全局的複合的UI。
一般fragment之間可能會須要交互，好比基於用戶事件改變fragment的內容。全部fragment之間的交互須要經過他們關聯的activity，兩個fragment之間不該該直接交互。
爲了讓fragment與activity交互，能夠在Fragment 類中定義一個接口，並在activity中實現。Fragment在他們生命週期的onAttach()方法中獲取接口的實現，而後調用接口的方法來與Activity交互。
下面是一個fragment與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"); } } ... }
如今Fragment就能夠經過調用OnHeadlineSelectedListener接口實例的mCallback中的onArticleSelected()（也能夠是其它方法）方法與activity傳遞消息。
舉個例子，下面這個在fragment中的方法將會在用戶點擊列表條目時被調用，fragment 用回調接口來傳遞事件給父Activity.
@Override public void onListItemClick(ListView l, View v, int position, long id) { // Send the event to the host activity mCallback.onArticleSelected(position); }
爲了接收回調事件，宿主activity必須實如今Fragment中定義的接口。
舉個例子，下面的activity實現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 } }
宿主activity經過findFragmentById()方法獲取fragment的實例，而後直接調用Fragment的public方法來向fragment傳遞消息。
例如，假設上面所示的activity可能包含另一個fragment,這個fragment用來展現從上面的回調方法中返回的指定的數據。在這種狀況下，activity能夠把從回調方法中接收到的信息傳遞給這個展現數據的Fragment.
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(); } } }
翻譯來自：