Android中有一个经常使用到的组件,叫Service,它有这么几个特点:
- 它无法与用户直接进行交互;
- 它必须由用户或者其他程序显式的启动;
- 它的优先级比较高,它比处于前台的应用优先级低,但是比后台的其他应用优先级高,这就决定了当系统因为缺少内存而销毁某些没被利用的资源时,它被销毁的概率很小。
那么接下来,我们就写一个比较简单的跟activity界面绑定的service,用于音乐播放,activity销毁时,服务service也销毁,音乐就停止播放。
看TestService.java:
/** * @author xpd3581 * @date 2017-3-27 * @version 1.0 */
package com.xingpd.test;
import java.io.IOException;
import android.app.Service;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.IBinder;
import android.util.Log;
/** * TestService 2017-3-27 */
public class TestService extends Service {
@Override
public IBinder onBind(Intent intent) {
Log.e("onBind:", "服务启动!");
new Thread() {
public void run() {
for (int i = 0; i < 100; i++) {
Log.e("i:", "====>" + i);
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}.start();
return null;
}
private MediaPlayer mp;
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.e("TestService:", "onStartCommand()!");
return super.onStartCommand(intent, flags, startId);
}
@Override
public void onStart(Intent intent, int startId) {
Log.e("TestService:", "onStart()!");
// 开始播放音乐
mp.start();
// 音乐播放完毕的事件处理
mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
public void onCompletion(MediaPlayer mp) {
// 循环播放
try {
mp.start();
} catch (IllegalStateException e) {
e.printStackTrace();
}
}
});
// 播放音乐时发生错误的事件处理
mp.setOnErrorListener(new MediaPlayer.OnErrorListener() {
public boolean onError(MediaPlayer mp, int what, int extra) {
// 释放资源
try {
mp.release();
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
});
super.onStart(intent, startId);
}
@Override
public void onCreate() {
Log.e("TestService:", "onCreate()!");
// 初始化音乐资源
try {
// 创建MediaPlayer对象
mp = new MediaPlayer();
// 将音乐保存在res/raw/era_themass.mp3,R.java中自动生成{public static final int
// era_themass=0x7f040000;}
mp = MediaPlayer.create(this, R.raw.era_themass);
// 在MediaPlayer取得播放资源与stop()之后要准备PlayBack的状态前一定要使用MediaPlayer.prepeare()
mp.prepare();
} catch (IllegalStateException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
super.onCreate();
}
@Override
public void onDestroy() {
Log.e("TestService:", "onDestroy()!");
// 服务停止时停止播放音乐并释放资源
mp.stop();
mp.release();
super.onDestroy();
}
@Override
public boolean onUnbind(Intent intent) {
Log.e("TestService:", "onUnbind()!");
return super.onUnbind(intent);
}
}
相关的资源配置:
服务写完以后,需要在AndroidManifest.xml文件里边注册:
<service android:name=".TestService">
</service>
然后启动服务和停止服务需要activity来实现:
MainActivity.java:
package com.xingpd.test;
import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity implements OnClickListener {
Button startService, stopService;
ServiceConnection sc = new ServiceConnection() {
@Override
public void onServiceDisconnected(ComponentName name) {
Log.e("ServiceConnection:", "onServiceDisconnected!");
}
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.e("ServiceConnection:", "onServiceConnected!");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
startService = (Button) this.findViewById(R.id.startService);
stopService = (Button) this.findViewById(R.id.stopService);
startService.setOnClickListener(this);
stopService.setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.startService:
Intent startIntent = new Intent(this, TestService.class);
startService(startIntent);
break;
case R.id.stopService:
Intent stopIntent = new Intent(this, TestService.class);
stopService(stopIntent);
break;
default:
break;
}
}
@Override
protected void onStop() {
// TODO Auto-generated method stub
Intent intent = new Intent(this, TestService.class);
stopService(intent);
super.onStop();
}
}
其中用的是startService方法,如果换成bindService方法就得需要下面的代码:
ServiceConnection sc = new ServiceConnection() {
@Override
public void onServiceDisconnected(ComponentName name) {
Log.e("ServiceConnection:", "onServiceDisconnected!");
}
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.e("ServiceConnection:", "onServiceConnected!");
}
};
而调用的话就是这样:
Intent startIntent = new Intent(this, TestService.class);
bindService(startIntent, sc, BIND_AUTO_CREATE);
同理,unbindService也是如此:
unbindService(sc);
项目运行以后,就可以点击相应按钮进行播放音乐了。
下载源码可以去这里: