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Android Handler 课程

热度：336 发布时间：2016-05-01 18:47:21.0

Android Handler 教程

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.

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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?++;??
????????}?????
????}??
}??

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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。

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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?++;??
????}??
}??

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下面我们看一下效果图:

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