如何给文字添加阴影效果

package com.loaderman.customviewdemo;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends Activity  {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView tv = (TextView)findViewById(R.id.tv);
        tv.setShadowLayer(2,5,5, Color.RED);
    }

}

<?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"
    >
    <TextView
        android:id="@+id/tv"
        android:layout_width="match_parent"
        android:text="动态代码阴影效果"
        android:layout_gravity="center"
        android:gravity="center"
        android:textSize="18sp"
        android:layout_height="wrap_content" />

    <TextView
        android:layout_width="match_parent"
        android:text="XML实现阴影效果"
        android:layout_gravity="center"
        android:gravity="center"
        android:textSize="18sp"
        android:shadowColor="@color/colorPrimary"
        android:shadowDx="5"
        android:shadowDy="5"
        android:shadowRadius="5"
        android:layout_height="wrap_content" />
</LinearLayout>

效果: