Android 启动后台运行程序(Service)

Android开发中，当需要创建在后台运行的程序的时候，就要使用到Service。Service 可以分为有无限生命和有限生命两种。

特别需要注意的是Service跟Activities是不同的（简单来说可以理解为后台与前台的区别），例如，如果需要使用Service的话，需要调用startService(),从而利用startService()去调用Service中的OnCreate()和onStart()方法来启动一个后台的Service。

启动一个Service的过程如下：context.startService() ->onCreate()- >onStart()->Service running其中onCreate()可以进行一些服务的初始化工作，onStart()则启动服务。

停止一个Service的过程如下：context.stopService() | ->onDestroy() ->Service stop

接下来的实例是一个利用后台服务播放音乐的小例子，点击start运行服务，点击stop停止服务。ServicesDemo.java（是一个Activity）

package com.android.myservice;  
  
import android.app.Activity;  
import android.content.Intent;  
import android.os.Bundle;  
import android.util.Log;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  
  
public class ServiceDemo extends Activity implements OnClickListener {  
private static final String TAG = "ServiceDemo";  
Button buttonStart, buttonStop;  
  
@Override  
public void onCreate(Bundle savedInstanceState) {  
super.onCreate(savedInstanceState);  
setContentView(R.layout.main);  
  
buttonStart = (Button) findViewById(R.id.buttonStart);  
buttonStop = (Button) findViewById(R.id.buttonStop);  
  
buttonStart.setOnClickListener(this);  
buttonStop.setOnClickListener(this);  
}  
  
public void onClick(View src) {  
switch (src.getId()) {  
case R.id.buttonStart:  
Log.i(TAG, "onClick: starting service");  
startService(new Intent(this, MyService.class));  
break;  
case R.id.buttonStop:  
Log.i(TAG, "onClick: stopping service");  
stopService(new Intent(this, MyService.class));  
break;  
}  
}  
}  

除此之外还要在Manifest里面声明服务:(AndroidManifest.xml)

<?xml version="1.0" encoding="utf-8"?>  
  
<manifest xmlns:android="http://schemas.android.com/apk/res/android"  
package="com.android.myservice">  
<application android:label="@string/app_name">  
<activity android:name=".ServiceDemo" android:label="@string/app_name">  
<intent-filter>  
<action android:name="android.intent.action.MAIN"/>  
<category android:name="android.intent.category.LAUNCHER"/>  
</intent-filter>  
</activity>  
<service android:enabled="true" android:name=".MyService"/>  
</application>  
</manifest>  

定义Service(MyService.java)

package com.android.myservice;  
  
import android.app.Service;  
import android.content.Intent;  
import android.media.MediaPlayer;  
import android.os.IBinder;  
import android.util.Log;  
import android.widget.Toast;  
  
public class MyService extends Service {  
private static final String TAG = "MyService";  
MediaPlayer player;  
  
@Override  
public IBinder onBind(Intent intent) {  
return null;  
}  
  
@Override  
public void onCreate() {  
Toast.makeText(this, "My Service created", Toast.LENGTH_LONG).show();  
Log.i(TAG, "onCreate");  
  
player = MediaPlayer.create(this, R.raw.braincandy);  
player.setLooping(false);  
}  
  
@Override  
public void onDestroy() {  
Toast.makeText(this, "My Service Stoped", Toast.LENGTH_LONG).show();  
Log.i(TAG, "onDestroy");  
player.stop();  
}  
  
@Override  
public void onStart(Intent intent, int startid) {  
Toast.makeText(this, "My Service Start", Toast.LENGTH_LONG).show();  
Log.i(TAG, "onStart");  
player.start();  
}  
}  

layout文件夹中是main.xml

<?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:gravity="center">  
<TextView  
android:layout_width="fill_parent"  
android:layout_height="wrap_content" android:text="@string/services_demo" android:gravity="center" android:textSize="20sp" android:padding="20dp"/>  
<Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/buttonStart" android:text="@string/start"></Button>  
<Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/stop" android:id="@+id/buttonStop"></Button>  
</LinearLayout>  

values 文件夹中是strings.xm

<?xml version="1.0" encoding="utf-8"?>  
  
<resources>  
<string name="start">Start</string>  
<string name="stop">Stop</string>  
<string name="services_demo">Service Demo</string>  
</resources>