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

<?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. */
    @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

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.