Android实现图片添加阴影效果的2种方法

<?xml version="1.0" encoding="utf-8"? 
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" 
 <!-- 阴影图片，android:left表示阴影图片左边到背景图片左边的距离
 android:top表示阴影图片上边到背景图片上边的距离-- 
 <item android:left="5dp"
  android:top="5dp" 
  <shape 
   <corners android:radius="25dp"/ 
   <solid android:color="#60000000"/ 
  </shape 
 </item 
 <!-- 背景图片，android:right表示阴影图片右边到背景图片右边的距离
 android:bottom表示阴影图片下边到背景图片下边的距离-- 
 <item android:bottom="5dp"
  android:right="5dp" 
  <shape 
   <corners android:radius="25dp"/ 
   <solid android:color="#000000"/ 
  </shape 
 </item 
</layer-list 

<?xml version="1.0" encoding="utf-8"? 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context="com.example.liusiyutaloner.frescotest.MainActivity" 

 <TextView
  android:layout_width="100dp"
  android:layout_height="100dp"
  android:background="@drawable/shadow_view"/ 
</RelativeLayout 

package com.example.liusiyutaloner.frescotest;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;

public class CustomShadowView extends View {
  private Paint mPaint;

  public CustomShadowView(Context context, AttributeSet attrs) {
   super(context, attrs);
   mPaint = new Paint();
   mPaint.setColor(Color.BLACK);
   this.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
  }

  @Override
  protected void onDraw(Canvas canvas) {
   super.onDraw(canvas);
   //绘制阴影，param1：模糊半径；param2：x轴大小：param3：y轴大小；param4：阴影颜色
   mPaint.setShadowLayer(10F, 15F, 15F, Color.GRAY);
   RectF rect = new RectF(0 , 0, 200, 200);
   canvas.drawRoundRect(rect, (float)75, (float)75, mPaint);
  }

}

<?xml version="1.0" encoding="utf-8"? 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="150dp"
 android:layout_height="150dp"
 tools:context="com.example.liusiyutaloner.frescotest.MainActivity" 

 <com.example.liusiyutaloner.frescotest.CustomShadowView
  android:layout_gravity="center"
  android:layout_width="125dp"
  android:layout_height="125dp"
  android:layout_centerHorizontal="true" / 
</RelativeLayout