Fragment之Creating event callbacks to activity实例

在看Android帮助文档的时候，会出现一些例子，但是例子总是穿插着多种知识，让还没有系统学过Android的人读起来很费神难懂,所以就自己写了一个creating event callbacks to activity的例子.

我把Activity的UI分为两个部分，左边和右边，左边用来放置点击的按钮(LeftFragment),右边用来放置对应点击后显示的信息(RightFragment).

Activity的布局layout文件：main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="horizontal" >    <LinearLayout        android:id="@+id/left_layout"        android:layout_width="wrap_content"        android:layout_height="fill_parent"        android:layout_weight="1"        android:orientation="vertical" >    </LinearLayout>    <LinearLayout        android:id="@+id/right_layout"        android:layout_width="wrap_content"        android:layout_height="fill_parent"        android:layout_weight="10"        android:orientation="vertical" >    </LinearLayout></LinearLayout>

LeftFragment的布局layout：leftfragment.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical" >    <Button        android:id="@+id/first_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/first_button" />    <Button        android:id="@+id/second_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/second_button" />    <Button        android:id="@+id/third_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/third_button" /></LinearLayout>

RightFragment的布局layout:rightfragment.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical" >    <TextView        android:id="@+id/right_show_message"        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:background="@android:color/holo_orange_dark"        android:textColor="@android:color/white" /></LinearLayout>

以上是两个fragment和一个Activity的布局文件，下面来看他们的java文件

Activity: 

public class FirstActivity extends Activity implements MyListener{/** * 实现MyListener,当LeftFragment中点击第一页的时候，让RightFragment显示第一页信息,同理当点击第二页的时候，RightFragment显示第二页信息 *  * @param index *            显示的页数 */public void showMessage(int index){if (1 == index)showMessageView.setText(R.string.first_page);if (2 == index)showMessageView.setText(R.string.second_page);if (3 == index)showMessageView.setText(R.string.third_page);}/** 得到RightFragment中显示信息的控件 */private TextView showMessageView;/** Called when the activity is first created. */@Overridepublic void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.main);System.out.println("Activity--->onCreate");FragmentManager manager = getFragmentManager();FragmentTransaction transaction = manager.beginTransaction();// 动态增加FragmentRightFragment rightFragment = new RightFragment();LeftFragment leftFragment = new LeftFragment();transaction.add(R.id.left_layout, leftFragment, "leftfragment");transaction.add(R.id.right_layout, rightFragment, "rightfragment");transaction.commit();}@Overrideprotected void onResume(){super.onResume();System.out.println("Activity--->onResume");showMessageView = (TextView) findViewById(R.id.right_show_message);}}

LeftFragment:

public class LeftFragment extends Fragment{/** Acitivity要实现这个接口，这样Fragment和Activity就可以共享事件触发的资源了 */public interface MyListener{public void showMessage(int index);}private MyListener myListener;private Button firstButton;private Button secondButton;private Button thirdButton;/** Fragment第一次附属于Activity时调用,在onCreate之前调用 */@Overridepublic void onAttach(Activity activity){super.onAttach(activity);System.out.println("LeftFragment--->onAttach");myListener = (MyListener) activity;}@Overridepublic void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);System.out.println("LeftFragment--->onCreate");}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){System.out.println("LeftFragment--->onCreateView");return inflater.inflate(R.layout.leftfragment, container, false);}@Overridepublic void onResume(){super.onResume();System.out.println("LeftFragment--->onResume");firstButton = (Button) getActivity().findViewById(R.id.first_button);secondButton = (Button) getActivity().findViewById(R.id.second_button);thirdButton = (Button) getActivity().findViewById(R.id.third_button);MyButtonClickListener clickListener = new MyButtonClickListener();firstButton.setOnClickListener(clickListener);secondButton.setOnClickListener(clickListener);thirdButton.setOnClickListener(clickListener);}/** 按钮的监听器 */class MyButtonClickListener implements OnClickListener{public void onClick(View v){Button button = (Button) v;if (button == firstButton)myListener.showMessage(1);if (button == secondButton)myListener.showMessage(2);if (button == thirdButton)myListener.showMessage(3);}}}

RightFragment:

public class RightFragment extends Fragment{@Overridepublic void onCreate(Bundle savedInstanceState){System.out.println("RightFragment--->onCreate");super.onCreate(savedInstanceState);}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){System.out.println("RightFragment--->onCreateView");return inflater.inflate(R.layout.rightfragment, container, false);}}

注意，Fragment的生命周期和Activity生命周期之间的关系。在Activity里动态生成Fragment，首先是Activity调用onCreate()方法，但是这时候还没有加载到Fragment里的组件，当Fragment调用其onCreateView()方法后，Activity才能得到Fragment中的组件.以下可以看到它们的生命周期情况:

图：

这里最关键的就是Fragment要有一个接口和这个接口的引用，而这个接口需要Activity去实现它。当Fragment调用onAttach(Activity acitivity)方法的时候，将这个activity传递给这个接口引用，这样，就可以和Activity进行交互了.