推荐安卓开发神器（里面有各种UI特效和android代码库实例）
android中开发中，有时候为了某种效果需要给ImageView 或者LinearLayout画阴影。
为ImageView画阴影的主要的思想利用已知图片，然后构造一个阴影的bitmap。最后设置阴影的bitmap作为ImageView的背景。
这里参考了一个帖子：http://stackoverflow.com/questions/3567312/android-drop-shadow-on-view
利用这个思想。构造代码如下：
public void drawImageDropShadow(){
BlurMaskFilter blurFilter = new BlurMaskFilter(3, BlurMaskFilter.Blur.OUTER);
Paint shadowPaint = new Paint();
shadowPaint.setMaskFilter(blurFilter);
int[] offsetXY =new int[2];
Bitmap originalBitmap = BitmapFactory.decodeResource(this.getResources(),R.drawable.favoritelist);
Bitmap shadowBitmap = originalBitmap.extractAlpha(shadowPaint,offsetXY);
Bitmap shadowImage32 = shadowBitmap.copy(Bitmap.Config.ARGB_8888, true);
Canvas c = new Canvas(shadowImage32);
c.drawBitmap(originalBitmap, 0,0, null);
ImageView imageView1 = (ImageView)findViewById(R.id.shadowImageView);
imageView1.setImageBitmap(shadowImage32);
}
下面是设置LinearLayout的背景。用xml文件画Rectangle来作为LinearLayout的背景。思想和前面的一样。不同的是通过.xml创建一个Drawable，然后
制定 宽和高， 将Drawable转化bitmap 画阴影bitmap，然后将阴影bitmap转化为drawable，最后将drawable设置为LinearLayout的背景。
代码如下：
说明需要一个方法：将drawable转化为bitmap
一般通用的方法为:
public static Bitmap drawableToBitmap(Drawable drawable) {
Bitmap bitmap = Bitmap
.createBitmap(
drawable.getIntrinsicWidth(),
drawable.getIntrinsicHeight(),
drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
: Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(bitmap);
//canvas.setBitmap(bitmap);
drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
drawable.draw(canvas);
return bitmap;
}
我创建的drawable是一个xml文件，而不是图片，所以，drawable.getIntrinsicHeight()得不到值。所以要手动传递参数设宽度和高度。代码如下：
private Bitmap drawableToBitmap(Drawable drawable,int width,int height) {
Bitmap bitmap = Bitmap.createBitmap(
width,
height,
drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
: Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(bitmap);
drawable.setBounds(0, 0, width, height);
drawable.draw(canvas);
return bitmap;
}
最后设置阴影的代码：
public void drawLayoutDropShadow(){
LinearLayout linearLayout = (LinearLayout)findViewById(R.id.testShadowLinearLayout);
BlurMaskFilter blurFilter = new BlurMaskFilter(3, BlurMaskFilter.Blur.OUTER);
Paint shadowPaint = new Paint();
shadowPaint.setMaskFilter(blurFilter);
Drawable drawable = this.getResources().getDrawable(R.drawable.backgroundservicescolor);
int[] offsetXY =new int[2];
Bitmap originalBitmap = drawableToBitmap(drawable,200,100);
Bitmap shadowBitmap = originalBitmap.extractAlpha(shadowPaint,offsetXY);
Bitmap shadowImage32 = shadowBitmap.copy(Bitmap.Config.ARGB_8888, true);
Canvas c = new Canvas(shadowImage32);
c.drawBitmap(originalBitmap, 0,0, null);
Drawable d =new BitmapDrawable(shadowImage32);
linearLayout.setBackgroundDrawable(d);
}
最后的效果如下：
