利用Handler来更新android的UI

一时失言乱红尘 2022-08-05 00:51 159阅读 0赞

原贴链接:http://rayleung.javaeye.com/blog/411860

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();     
                    \}     
               \}     
          \}     
     \}     
\}

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