android中fragment与activity之间通信

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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

<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

<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="firstButton"/> 
   
    <Button
        android:id="@+id/second_button"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="second_button"/> 
   
    <Button
        android:id="@+id/third_button"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="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:

package com.example.fragmentandactivity;

import com.example.fragmentandactivity.LeftFragment.MyListener;

import android.os.Bundle;
import android.app.Activity;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends FragmentActivity implements MyListener{
	 /** 得到RightFragment中显示信息的控件 */  
    private TextView showMessageView;  
	  /** 
     * 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("第一页");  
	        if(2 == index)   
	            showMessageView.setText("第二页");  
	        if(3 == index)   
	            showMessageView.setText("第三页");  
	    } 

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		 System.out.println("Activity--->onCreate");  
		 
		 FragmentManager manager = 	getSupportFragmentManager();
		 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);   
	    } 

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}

LeftFragment:

package com.example.fragmentandactivity;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;

public class LeftFragment extends Fragment{
	   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);  
        }  
    }  

	 /** 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);   
    }  

}

RightFragment:

package com.example.fragmentandactivity;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

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.