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。
程序运行界面:
代码:
定义服务,MyService.java
- package com.example;
-
- 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.d(TAG, "onCreate");
-
- player = MediaPlayer.create(this, R.raw.braincandy);
- player.setLooping(false);
- }
-
- @Override
- public void onDestroy() {
- Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
- Log.d(TAG, "onDestroy");
- player.stop();
- }
-
- @Override
- public void onStart(Intent intent, int startid) {
- Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show();
- Log.d(TAG, "onStart");
- player.start();
- }
- }
package com.example;
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.d(TAG, "onCreate");
player = MediaPlayer.create(this, R.raw.braincandy);//运行例子是,需要替换音乐的名称
player.setLooping(false); // Set looping
}
@Override
public void onDestroy() {
Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
Log.d(TAG, "onDestroy");
player.stop();
}
@Override
public void onStart(Intent intent, int startid) {
Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show();
Log.d(TAG, "onStart");
player.start();
}
}
除此之外还要在Manifest里面声明服务:
- xml version="1.0" encoding="utf-8"?>
- <manifest xmlns:android=""
- package="com.example" android:versionCode="1" android:versionName="1.0">
- <application android:icon="@drawable/icon" android:label="@string/app_name">
- <activity android:name=".ServicesDemo" 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>
- <uses-sdk android:minSdkVersion="3" />
- manifest>
定义Activity,ServicesDemo.java
- package com.example;
-
- 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 ServicesDemo extends Activity implements OnClickListener {
- private static final String TAG = "ServicesDemo";
- 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.d(TAG, "onClick: starting srvice");
- startService(new Intent(this, MyService.class));
- break;
- case R.id.buttonStop:
- Log.d(TAG, "onClick: stopping srvice");
- stopService(new Intent(this, MyService.class));
- break;
- }
- }
- }
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