学步园

原作者：

文字程序很简单，一个View，一个Activity，利用handler和postInvalidate()更新UI。

程序效果是一个蓝色的正方形向右移出屏幕。

Java代码  

1. package com.ray.test;  
2.   
3. import android.app.Activity;  
4. import android.content.Context;  
5. import android.graphics.Canvas;  
6. import android.graphics.Color;  
7. import android.graphics.Paint;  
8. import android.os.Bundle;  
9. import android.os.Handler;  
10. import android.view.View;  
11.   
12. public class TestHandler extends Activity {  
13.     private MyView myView;  
14.     private Handler mHandler;  
15.     public void onCreate(Bundle savedInstanceState) {  
16.         super.onCreate(savedInstanceState);  
17.         myView = new MyView(this);  
18.         mHandler = new Handler();  
19.         mHandler.post(update);  
20.         setContentView(myView);  
21.     }  
22.       
23.     private Runnable update = new Runnable() {  
24.         public void run() {  
25.             myView.update();  
26.             mHandler.postDelayed(update, 5);  
27.         }  
28.     };  
29.       
30.     class MyView extends View{  
31.           
32.         private float x = 0f;  
33.         public MyView(Context context) {  
34.             super(context);  
35.               
36.         }  
37.           
38.         public void update(){  
39.             postInvalidate();  
40.         }  
41.         protected void onDraw(Canvas canvas) {  
42.             super.onDraw(canvas);  
43.             x+=1;  
44.             Paint mPaint = new Paint();  
45.             mPaint.setColor(Color.BLUE);  
46.             canvas.drawRect(x, 40, x+40, 80, mPaint);  
47.         }  
48.           
49.     }  
50. }  

package com.ray.test;

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.view.View;

public class TestHandler extends Activity {
	private MyView myView;
	private Handler mHandler;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        myView = new MyView(this);
        mHandler = new Handler();
        mHandler.post(update);
        setContentView(myView);
    }
    
    private Runnable update = new Runnable() {
        public void run() {
            myView.update();
            mHandler.postDelayed(update, 5);
        }
    };
    
    class MyView extends View{
    	
    	private float x = 0f;
		public MyView(Context context) {
			super(context);
			
		}
		
		public void update(){
			postInvalidate();
		}
		protected void onDraw(Canvas canvas) {
			super.onDraw(canvas);
			x+=1;
			Paint mPaint = new Paint();
			mPaint.setColor(Color.BLUE);
			canvas.drawRect(x, 40, x+40, 80, mPaint);
		}
    	
    }
}

 之前还写过另外一篇关于Handler更新UI的文章：

http://rayleung.iteye.com/blog/411860

回复人：（不需要handler)

你的两篇文章对于invalidate()和postInvalidate()认识有些问题
http://www.iteye.com/topic/435147
http://rayleung.iteye.com/blog/411860

调用Handler.post(Runnable r)方法,Runnable运行在UI所在线程,所以可以直接调用View.invalidate()

Java代码  

1. package com.ray.test;  
2.   
3. import android.app.Activity;  
4. import android.content.Context;  
5. import android.graphics.Canvas;  
6. import android.graphics.Color;  
7. import android.graphics.Paint;  
8. import android.os.Bundle;  
9. import android.os.Handler;  
10. import android.view.View;  
11.   
12. public class TestHandler extends Activity {  
13.     private MyView myView;  
14.     private Handler mHandler;  
15.     public void onCreate(Bundle savedInstanceState) {  
16.         super.onCreate(savedInstanceState);  
17.         myView = new MyView(this);  
18.         mHandler = new Handler();  
19.         mHandler.post(new Runnable(){  
20.             @Override  
21.             public void run() {  
22.                 myView.invalidate();  
23.                 mHandler.postDelayed(this, 5);  
24.             }  
25.          });  
26.         setContentView(myView);  
27.     }  
28.       
29.     class MyView extends View{  
30.         private float x = 0f;  
31.         public MyView(Context context) {  
32.             super(context);  
33.               
34.     }  
35.         protected void onDraw(Canvas canvas) {  
36.             super.onDraw(canvas);  
37.             x+=1;  
38.             Paint mPaint = new Paint();  
39.             mPaint.setColor(Color.BLUE);  
40.             canvas.drawRect(x, 40, x+40, 80, mPaint);  
41.         }  
42.           
43.     }  
44. }  

package com.ray.test;

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.view.View;

public class TestHandler extends Activity {
	private MyView myView;
	private Handler mHandler;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        myView = new MyView(this);
        mHandler = new Handler();
        mHandler.post(new Runnable(){
			@Override
			public void run() {
				myView.invalidate();
				mHandler.postDelayed(this, 5);
			}
         });
        setContentView(myView);
    }
    
    class MyView extends View{
    	private float x = 0f;
		public MyView(Context context) {
			super(context);
			
	}
		protected void onDraw(Canvas canvas) {
			super.onDraw(canvas);
			x+=1;
			Paint mPaint = new Paint();
			mPaint.setColor(Color.BLUE);
			canvas.drawRect(x, 40, x+40, 80, mPaint);
		}
    	
    }
}

在新线程里更新UI,可以直接postInvalidate()

Java代码  

1. public void onCreate(Bundle savedInstanceState) {      
2.                super.onCreate(savedInstanceState);      
3.                this.requestWindowFeature(Window.FEATURE_NO_TITLE);      
4.      
5.                myView = new MyView(this);  
6.        this.setContentView(this.myView);      
7.        new Thread(new myThread()).start();     
8. }      
9.     
10.     class myThread implements Runnable {      
11.           public void run() {     
12.               while (!Thread.currentThread().isInterrupted()) {      
13.                    try {  
14.                           myView.postInvalidate();   
15.                         Thread.sleep(100);       
16.                    } catch (InterruptedException e) {      
17.                         Thread.currentThread().interrupt();      
18.                    }      
19.                }      
20.           }      
21.     }