Android开发：ImageView阴影和图层效果

import Android.app.Activity;  
import Android.content.Context;  
import Android.graphics.Bitmap;  
import Android.graphics.BitmapFactory;  
import Android.graphics.Canvas;  
import Android.graphics.Color;  
import Android.graphics.Paint;  
import Android.graphics.PorterDuff;  
import Android.graphics.PorterDuff.Mode;  
import Android.graphics.PorterDuffXfermode;  
import Android.graphics.Rect;  
import Android.graphics.RectF;  
import Android.graphics.drawable.Drawable;  
import Android.os.Bundle;  
import Android.view.View;  
  
public class MyCanvasActivity extends Activity {  
      
    @Override  
    public
void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(new
ImageEffect(this));  
    }  
      
  class
ImageEffect extends View{  
      Paint
paint;  
     public
ImageEffect(Context context){  
         super(context);  
         paint=
new Paint(); //初始化画笔，为后面阴影效果使用。   
         paint.setAntiAlias(true);//去除锯齿。   
         paint.setShadowLayer(5f,
5.0f, 5.0f, Color.BLACK); //设置阴影层，这是关键。   
         paint.setXfermode(new
PorterDuffXfermode(Mode.SRC_IN));  
           
     }  
     public
void onDraw(Canvas canvas){  
         super.onDraw(canvas);  
         int
posX  =
20;  
         int
posY = 50;  
         int
PicWidth,PicHeight;  
           
        Drawable
drawable = getResources().getDrawable(R.drawable.pic);  
        Drawable
dbe    =
getResources().getDrawable(R.drawable.pic).mutate();//如果不调用mutate方法，则原图也会被改变，因为调用的资源是同一个，所有对象是共享状态的。   
        Drawable
drawTest = getResources().getDrawable(R.drawable.pic);