给图片加阴影效果简单示例代码实现

package com.loaderman.customviewdemo;

import android.content.Context;
import android.graphics.*;
import android.util.AttributeSet;
import android.view.View;

public class BitmapShadowView extends View {
    private Paint mPaint;
    private Bitmap mBitmap, mAlphaBmp;

    public BitmapShadowView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setLayerType(LAYER_TYPE_SOFTWARE, null);
        mPaint = new Paint();
        mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.cat_dog);
        mAlphaBmp = mBitmap.extractAlpha();//抽取只有alpha值图片的函数
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        int width = 200;
        int height = width * mAlphaBmp.getWidth() / mAlphaBmp.getHeight();

        //绘制阴影
        mPaint.setColor(Color.GRAY);
        mPaint.setMaskFilter(new BlurMaskFilter(10, BlurMaskFilter.Blur.NORMAL));//
        canvas.drawBitmap(mAlphaBmp, null, new Rect(10, 10, width, height), mPaint);

        //绘制原图像
        canvas.translate(-5, -5);
        mPaint.setMaskFilter(null);
        canvas.drawBitmap(mBitmap, null, new Rect(0, 0, width, height), mPaint);
    }


}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_gravity="center"
    android:gravity="center"
    android:background="@android:color/white"
    >
  <com.loaderman.customviewdemo.BitmapShadowView
      android:layout_width="match_parent"
      android:layout_height="match_parent" />
</LinearLayout>

效果: