利用Handler来更新android的UI(1)

利用Handler来更新android的UI(1)

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。


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();
                    }
               }
          }
     }
}