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 {
-
-
- 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 {
-
-
- 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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