利用handler更新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

Java代码  

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。

首先创建简单的View,代码如下：

Java代码  

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：

Java代码  

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();   
                    }   
               }   
          }   
     }   
}