使用Android的线程实现View画图  

过去习惯捣鼓JavaSE,画图什么的很轻松.结果到了Android画图的处理发生很大改变,这篇暂时研究View画图,后面再写一篇关于SurfaceView画图的
Android是单线程处理模型的,如果要并发线程无法更新主View,否则Android就会认为线程干扰错误,例如下面的代码就是错的:

 new Thread( new Runnable() {
    public void run() {
         myView.invalidate();
     }
}).start();

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 org.c30;

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 org.c30;

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 UPMSG = 111; 

     Thread myRefreshThread = null;
     BounceView myBounceView = null; 

     Handler myHandler = new Handler() {
          public void handleMessage(Message msg) {
               switch (msg.what) {
                    case TestHandler.UPMSG :
                         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.UPMSG; 

                    TestHandler.this.myHandler.sendMessage(message);
                    try {
                         Thread.sleep(100);
                    } catch (InterruptedException e) {
                         Thread.currentThread().interrupt();
                    }
               }
          }
     }
}

 

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