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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: view plaincopy to clipboardprint? 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: view plaincopy to clipboardprint? 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 ++; } }

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