利用Handler来更新android的UI
刚刚开始接触android线程编程的时候，习惯好像java一样，试图用下面的代码解决问题new Thread( new Runnable() { public void run() { myView.invalidate(); } }).start();
然而发现这样是不行的，因为它违背了单线程模型：Android UI操作并不是线程安全的并且这些操作必须在UI线程中执行。查阅了文档和apidemo后，发觉常用的方法是利用Handler来实现UI线程的更新的。
下面代码的功能很简单：画一个圆出来，每隔0.1秒，圆向10移动10个像素。但可以清楚展示利用Handler更新UI的流程。
http://www.agoit.com/upload/picture/pic/38944/1ebc7f50-7e2f-3a14-8144-f71c7fdabe25.jpg
首先创建简单的View,代码如下：
package com.ray.handler;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Point;import android.graphics.drawable.Drawable;import android.view.View;public class BounceView extends View { float x = 40; public BounceView(Context context) { super(context); } @Override protected void onDraw(Canvas canvas) { x+=10; Paint mPaint = new Paint(); mPaint.setAntiAlias(true); mPaint.setColor(Color.GREEN); canvas.drawCircle(x, 40, 40, mPaint); }}
创建Activity，代码如下：
package com.ray.handler;import android.app.Activity;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.view.Window;public class TestHandler extends Activity { protected static final int GUIUPDATEIDENTIFIER = 0x101; Thread myRefreshThread = null; BounceView myBounceView = null; Handler myHandler = new Handler() { public void handleMessage(Message msg) { switch (msg.what) { case TestHandler.GUIUPDATEIDENTIFIER: myBounceView.invalidate(); break; } super.handleMessage(msg); } }; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); this.requestWindowFeature(Window.FEATURE_NO_TITLE); this.myBounceView = new BounceView(this); this.setContentView(this.myBounceView); new Thread(new myThread()).start(); } class myThread implements Runnable { public void run() { while (!Thread.currentThread().isInterrupted()) { Message message = new Message(); message.what = TestHandler.GUIUPDATEIDENTIFIER; TestHandler.this.myHandler.sendMessage(message); try { Thread.sleep(100); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } } } }
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