android中fragment与activity之间通信原理以及例子

摘要 首先,如果你想在android3.0及以下版本使用fragment,你必须引用android-support-v4.jar这个包 然后你写的activity不能再继承自Activity类了,而是要继承android.support.v4.app.FragmentActivity,一些其他的父类也有相应的变化. 由于在android的实现机制中frag

首先,如果你想在android3.0及以下版本使用fragment,你必须引用android-support-v4.jar这个包

然后你写的activity不能再继承自Activity类了,而是要继承android.support.v4.app.FragmentActivity,一些其他的父类也有相应的变化.

由于在android的实现机制中fragment和activity会被分别实例化为两个不相干的对象,他们之间的联系由activity的一个成员对象fragmentmanager来维护.fragment实例化后会到activity中的fragmentmanager去注册一下,这个动作封装在fragment对象的onAttach中,所以你可以在fragment中声明一些回调接口,当fragment调用onAttach时,将这些回调接口实例化,这样fragment就能调用各个activity的成员函数了,当然activity必须implements这些接口,否则会包classcasterror

fragment和activity的回调机制又是OOP的一次完美演绎!

下面通过一个例子来说明：

 

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

 

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<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas./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

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<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas./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

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<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas./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:

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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. */     @Override     public 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Fragment         RightFragment 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();         }         @Override     protected void onResume()     {         super.onResume();         System.out.println("Activity--->onResume");         showMessageView = (TextView) findViewById(R.id.right_show_message);     } }

LeftFragment:

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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 */     @Override     public void onAttach(Activity activity)     {         super.onAttach(activity);         System.out.println("LeftFragment--->onAttach");             myListener = (MyListener) activity;     }         @Override     public void onCreate(Bundle savedInstanceState)     {         super.onCreate(savedInstanceState);         System.out.println("LeftFragment--->onCreate");     }         @Override     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)     {         System.out.println("LeftFragment--->onCreateView");         return inflater.inflate(R.layout.leftfragment, container, false);     }         @Override     public 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:

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public class RightFragment extends Fragment {     @Override     public void onCreate(Bundle savedInstanceState)     {         System.out.println("RightFragment--->onCreate");         super.onCreate(savedInstanceState);     }         @Override     public 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

 

 

 

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.