Android高手进阶教程(九)之----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:

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:

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 ++; } }

下面我们看一下效果图: