from:

http://www.oschina.net/question/54100_29060

The android canvas has many fun functions to help me to draw the view . The warning point is , onDraw function WILL NOT update every frame automatically, must call the invalidate() to force it to refresh the screen.

Remember the OpenGL ES ,  in the Renderer , onDrawFrame(GL10 gl) will update automatically every frame to refresh the screen.

But the advantage of the canvas is , it can drawBitmap as the java SDK default !

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package com.drawviewtest;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.opengl.Matrix;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DrawViewTest extends Activity
{
    
    private Paint paint;
    private int i=0;
    private int times=1;
    
    
    private class DrawView extends View{
        
        public DrawView(Context context){
            super(context);
            
            //draw text part
//            paint=new Paint();
//            paint.setColor(Color.GREEN);
//            paint.setTextSize(25);
//            paint.setAntiAlias(true);
            
            //dynamic draw part
            paint=new Paint();
            paint.setColor(Color.GREEN);
            paint.setAntiAlias(true);
            paint.setStyle(Paint.Style.STROKE);
            
            
        }

        @Override
        protected void onDraw(Canvas canvas) {
            
            //draw text part
//            super.onDraw(canvas);
//            // text, x, y, paintParam
//            canvas.drawText("Hello world", 5, 230, paint);
//            
//            this.invalidate();
            
            
            //dynamic draw part
            super.onDraw(canvas);
            Log.i("l","this run"+i+"times!");
            
            canvas.drawArc(new RectF(60,120,260,320), 0, i, true, paint);
            
            if(i<360){
                i+=10;
            }
            else{
                i=0;
            }
            
            
            try {
                Thread.sleep(500);
            } catch (Exception ex) {
                Log.i("l","thread exception:"+ex);
            }
            
            
            
            
            this.invalidate();
        }
        
        
    
    }
    
    
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(new DrawView(this));
    }
}