android中fragment与activity之间通信原理以及例子

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,否则会报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

<?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

FirstActivity：

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:

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:

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