Android开发之根据Service的生命周期特点后台连接网络下载图片（源代码分享）

       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;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);button=(Button)this.findViewById(R.id.button1);button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubIntent intent=new Intent(MainActivity.this,DownLoadService.class);startService(intent);//通过intent启动service}});}@Overridepublic 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}};};@Overridepublic IBinder onBind(Intent intent) {// TODO Auto-generated method stubreturn null;}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {// TODO Auto-generated method stubnew Thread(new MyThread()).start();//启动线程return super.onStartCommand(intent, flags, startId);}@Overridepublic void onCreate() {// TODO Auto-generated method stubsuper.onCreate();}public class MyThread implements Runnable {@Overridepublic void run() {// TODO Auto-generated method stubHttpClient 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trueif (flag) {handler.sendEmptyMessage(1);//通过handler发送消息}} catch (ClientProtocolException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.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 blocke.printStackTrace();}} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();}finally{if (fileOutputStream!=null) {try {fileOutputStream.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}return flag;}}