android中的服务与其他软件的服务可能有些不同,它用来实现在后台执行长期的任务,并且与前台界面解耦.现在来实现一个HelloWorld级的服务以及使用这个服务,创建一个服务的步骤如下:
1.编写aidl文件,在这个文件中提供了服务所提供的方法的接口,文件的扩展名为aidl,在我们的示例中命名为IDataTimeService.aidl文件的内容为如下所示:
Java代码
package com.services.demo2;
// Declare the interface.
interface IDataTimeService {
String getForecastPage();
}
2.编写服务的实现类,在这个示例中为DataTimeService.java,内容如下:
Java代码
public class DataTimeService extends Service{
public static final String BROADCAST_ACTION = "com.services.demo2.DataTimeServiceEvent";
/**
使用上面定义的字符串常量创建一个Intent的实例,如果服务在运行的过程中发生的事件都可以通过Service的
sendBroadcast(broadcast)方法来发送一个广播消息通知Activity,然后有Activity注册的接收者进行处理;
*/
private Intent broadcast = new Intent(BROADCAST_ACTION);
sendBroadcast(broadcast);
private final IDataTimeService.Stub binder = new IDataTimeService.Stub() {
public String getForecastPage() {
return (getForecastPageImpl());
}
};
synchronized private String getForecastPageImpl() {
Date date=new Date();
return (date.toLocaleString());
}
@Override
public IBinder onBind(Intent intent) {
return (binder);
}
}
3.现在编写一个Activity,来消费这个服务:
Java代码
public class ServicesDemo2 extends Activity {
private IDataTimeService service = null;
private Intent serviceIntent = null;
private WebView browser;
private ServiceConnection svcConn = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder binder) {
service = IDataTimeService.Stub.asInterface(binder);
browser.postDelayed(new Runnable() {
public void run() {
updateForecast();
}
}, 1000);
}
public void onServiceDisconnected(ComponentName className) {
service = null;
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
browser = (WebView) findViewById(R.id.webkit);
serviceIntent = new Intent(this, DataTimeServiceImpl.class);
//绑定一个服务
bindService(serviceIntent, svcConn, BIND_AUTO_CREATE);
}
@Override
public void onResume() {
super.onResume();
/**
注册广播消息的接收者,在android中服务与Activity的通信依靠广播发送消息,然后由Activity注册的接收者
接收到消息,进行相应的处理这里使用DataTimeServiceImpl.BROADCAST_ACTION来过滤,表明它只接收
DataTimeService中的调用sendBroadcast(broadcast)发送的广播消息;
*/
registerReceiver(receiver, new IntentFilter(
DataTimeServiceImpl.BROADCAST_ACTION));
}
@Override
public void onPause() {
super.onPause();
unregisterReceiver(receiver);
}
@Override
public void onDestroy() {
super.onDestroy();
unbindService(svcConn);
}
private void updateForecast() {
try {
String page = service.getForecastPage();
if (page != null) {
browser.loadDataWithBaseURL(null, page, "text/html", "UTF-8",null);
browser.postDelayed(new Runnable() {
public void run() {
updateForecast();
}
}, 1000);
}
} catch (final Throwable t) {
svcConn.onServiceDisconnected(null);
}
}
//接收者实例
private BroadcastReceiver receiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
runOnUiThread(new Runnable() {
public void run() {
updateForecast();
}
});
}
};
}
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