Android 如何清空 Canvas ?（找了好久的答案）

Android 如何清空　Canvas ?

似乎一直未找到好的解决办法，有的方法限制使用纯色背景，但无论怎么尝试，都未见效果，

终于在　http://stackoverflow.com/questions/4650755/clearing-canvas-with-canvas-drawcolor　　上面找到了答案：

经过尝试，结果如下：

　　　　　

之前的不理想图片　　　　　　　　　　　　　　　　　　　　　想要的效果

（注，图示方向为最顶层）

此类如下：

package com.test.move;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.PorterDuff.Mode;import android.graphics.PorterDuffXfermode;import android.util.AttributeSet;import android.view.SurfaceHolder;import android.view.SurfaceHolder.Callback;import android.view.SurfaceView;import com.test.R;public class GlobalMove extends SurfaceView implements Callback, Runnable {public final static String TAG = "GlobalMove";public static int count = 0;private boolean bSurfaceRun = true;private SurfaceHolder sh;private Thread   th;    private Paint p;       private Canvas canvas;  //objects to be moved...private Bitmap bmp;private int lastX = 0;public GlobalMove(Context context, AttributeSet attrs) {//这种写法。。。super(context, attrs);sh = this.getHolder();sh.addCallback(this);th = new Thread(this);p = new Paint();initComponents(context);}private void initComponents(Context context){bmp = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon); }private void draw(){canvas = sh.lockCanvas();if(canvas != null){

//取消如下四行注释看效果。//Paint paint = new Paint();//paint.setXfermode(new PorterDuffXfermode(Mode.CLEAR));//canvas.drawPaint(paint);//paint.setXfermode(new PorterDuffXfermode(Mode.SRC));canvas.drawBitmap(bmp, lastX+10, 50, p);}lastX += 10;if(lastX > 400)lastX = 0;sh.unlockCanvasAndPost(canvas);}@Overridepublic void run() {while(bSurfaceRun){draw();try{Thread.sleep(100);} catch(InterruptedException  e){                e.printStackTrace();  }}}///////////////////////////////////////////////////////////////////////////////////////////////////@Overridepublic void surfaceCreated(SurfaceHolder holder) {th.start();}@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width,int height) {}@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {bSurfaceRun = false;} }