MainActivity:

package com.hyzhou.imagedemo;import java.io.File;import android.os.Bundle;import android.os.Environment;import android.app.Activity;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.view.Menu;public class MainActivity extends Activity {	@Override	protected void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		//设置当前Activity界面布局		setContentView(R.layout.activity_main);		//SD卡路径		File sd=Environment.getExternalStorageDirectory();		String path=sd.getPath()+"/image/zhizhi.jpg";		//通过BitmapFactory获得Bitmap实例		Bitmap bm=BitmapFactory.decodeFile(path);		try {			//设置桌面			setWallpaper(bm);		} catch (Exception e) {			e.printStackTrace();		}	}	@Override	public boolean onCreateOptionsMenu(Menu menu) {		// Inflate the menu; this adds items to the action bar if it is present.		getMenuInflater().inflate(R.menu.activity_main, menu);		return true;	}}

注意：一定要记得在Android Manifest.xml中加入下面语句，声明拥有修改壁纸的权限，不然setWallpaper()方法不起作用

<uses-permission  android:name="android.permission.SET_WALLPAPER"/>