Android Handler的使用!!!

大家好我们这一节讲的是Android Handler的使用,在讲Handler之前，我们先提个小问题，就是如何让程序5秒钟更新一下Title.
首先我们看一下习惯了Java编程的人，在不知道Handler的用法之前是怎么样写的程序,代码如下所示:
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package com.android.tutor; 
import java.util.Timer; 
import java.util.TimerTask; 
import android.app.Activity; 
import android.os.Bundle; 
public class HandlerDemo extends Activity { 
     
    //title为setTitle方法提供变量,这里为了方便我设置成了int型 
    private int title = 0; 
     
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
         
        Timer timer = new Timer(); 
        timer.scheduleAtFixedRate(new MyTask(), 1, 5000); 
    } 
         
    private class MyTask extends TimerTask{ 
        @Override 
        public void run() { 
             
            setTitle("Welcome to Mr Wei's blog " + title); 
            title ++; 
        }    
    } 
} 
package
com.android.tutor;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.os.Bundle;
public class HandlerDemo extends Activity {
   
//title为setTitle方法提供变量,这里为了方便我设置成了int型
private int title = 0;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new MyTask(), 1, 5000);
    }
       
    private class MyTask extends TimerTask{
@Override
public void run() {

setTitle("Welcome to Mr Wei's blog " + title);
title ++;
} 
    }
}
然而当我们执行程序，并不能达到我们预期的效果，所以Android 引进了Handler 这个特殊的类，可以说它是Runnable和Activity交互的桥梁
，所以我们只要在run方法中发送Message,而在Handler里，通过不同的Message执行不同的任务。
所以我们修改后的代码如下:
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package com.android.tutor; 
import java.util.Timer; 
import java.util.TimerTask; 
import android.app.Activity; 
import android.os.Bundle; 
import android.os.Handler; 
import android.os.Message; 
public class HandlerDemo extends Activity { 
     
    //title为setTitle方法提供变量,这里为了方便我设置成了int型 
    private int title = 0; 
     
    private Handler mHandler = new Handler(){ 
         
        public void handleMessage(Message msg) { 
            switch (msg.what) { 
            case 1: 
                updateTitle(); 
                break; 
            } 
        }; 
    }; 
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
         
        Timer timer = new Timer(); 
        timer.scheduleAtFixedRate(new MyTask(), 1, 5000); 
    } 
         
    private class MyTask extends TimerTask{ 
        @Override 
        public void run() { 
             
            Message message = new Message(); 
            message.what = 1; 
            mHandler.sendMessage(message); 
             
        }    
    } 
     
     
    public void updateTitle(){ 
         
        setTitle("Welcome to Mr Wei's blog " + title); 
        title ++; 
    } 
} 
package
com.android.tutor;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
public class HandlerDemo extends Activity {
   
//title为setTitle方法提供变量,这里为了方便我设置成了int型
private int title = 0;

private Handler mHandler = new Handler(){

public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
updateTitle();
break;
}
};
};
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new MyTask(), 1, 5000);
    }
       
    private class MyTask extends TimerTask{
@Override
public void run() {

Message message = new Message();
message.what = 1;
mHandler.sendMessage(message);

} 
    }
   
   
    public void updateTitle(){
   
    setTitle("Welcome to Mr Wei's blog " + title);
title ++;
    }
}