上一章讲到Service在后台启动后不会自动销毁掉，其销毁的方式有两种一个是在外部使用stopService()方法，一个就是在继承Service的类下调用stopSelf()，那么应该何时调用stopself（）方法呢，如果不调用的话，service在后台会一直处在连接网络的状态，其内耗是可想而知的。这篇博文就会向大家介绍如果使用handle的信息传送机制来停止service的后台运行。‘
MainActivity
package com.example.f21_service01;import android.os.Bundle;import android.app.Activity;import android.content.Intent;import android.view.Menu;import android.view.View;import android.widget.Button;public class MainActivity extends Activity { private Button button; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); button=(Button)this.findViewById(R.id.button1); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub Intent intent=new Intent(MainActivity.this,DownLoadService.class); startService(intent);//通过intent启动service } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; }}MainActivity中的代码很简单，通过按下按钮来启动一个service，在这里还得强调一下service要记得在清单文件中声明，要不然会报错的。
DownloadService的代码
package com.example.f21_service01;import java.io.IOException;import org.apache.http.HttpResponse;import org.apache.http.client.ClientProtocolException;import org.apache.http.client.HttpClient;import org.apache.http.client.methods.HttpPost;import org.apache.http.impl.client.DefaultHttpClient;import org.apache.http.util.EntityUtils;import android.app.Service;import android.content.Intent;import android.os.Handler;import android.os.IBinder;import android.os.Message;public class DownLoadService extends Service { private static final String path = "http://my.csdn.net/u013900875"; private Handler handler = new Handler() { public void handleMessage(Message msg) { if (msg.what == 1) { stopSelf(); //当系统接收到消息后，关闭service } }; }; @Override public IBinder onBind(Intent intent) { // TODO Auto-generated method stub return null; } @Override public int onStartCommand(Intent intent, int flags, int startId) { // TODO Auto-generated method stub new Thread(new MyThread()).start();//启动线程 return super.onStartCommand(intent, flags, startId); } @Override public void onCreate() { // TODO Auto-generated method stub super.onCreate(); } public class MyThread implements Runnable { @Override public void run() { // TODO Auto-generated method stub HttpClient client = new DefaultHttpClient(); HttpPost httpPost = new HttpPost(path); try { HttpResponse httpResponse = client.execute(httpPost); byte[] result = EntityUtils.toByteArray(httpResponse .getEntity());//使用http协议下载图片 boolean flag = SDcardtoFile.WriteToFile("hello", result);//当成功写入内存卡后，将标志设为true if (flag) { handler.sendEmptyMessage(1);//通过handler发送消息 } } catch (ClientProtocolException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }}在startCommand()启动下载的线程，当下载完成后并且成功写入内存卡后，将flag置位true，通过handler的sendMessage()方法发送，然后调用stopself()，那为什么不直接调用这个方法呢，因为调用这个方法service的停止时间是不确定的，后面的代码还是会执行的。
最后再来回顾下之前前的sdcard的存入方法的书写
package com.example.f21_service01;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import android.os.Environment;public class SDcardtoFile { public static boolean WriteToFile(String name, byte[] data) { boolean flag = false; String state = Environment.getExternalStorageState(); FileOutputStream fileOutputStream = null; if (state.equals(Environment.MEDIA_MOUNTED)) { File file = new File(Environment.getExternalStorageDirectory(), name); try { fileOutputStream=new FileOutputStream(file); try { fileOutputStream.write(data, 0, data.length); flag=true; } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); }finally{ if (fileOutputStream!=null) { try { fileOutputStream.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } } return flag; }}