我一直在学习《Pro Android 2》这本书。我正在学习一个包含两个类的服务示例:BackgroundService.java和MainActivity.java。MainActivity声称(错误地?)它启动了服务,如下面的Log.d调用所示:
public class MainActivity extends Activity {
private static final String TAG = "MainActivity";
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.d(TAG, "starting service");
Button bindBtn = (Button)findViewById(R.id.bindBtn);
bindBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
Intent backgroundService = new Intent(MainActivity.this, com.marie.mainactivity.BackgroundService.class);
startService(backgroundService);
}
});
Button unbindBtn = (Button)findViewById(R.id.unbindBtn);
unbindBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
stopService(new Intent(MainActivity.this, BackgroundService.class));
}
});
}
}
我感到困惑的是UI提供了两个按钮:Bind和UnBind,如上所示。但根据文档,如果onBind()返回null,则表示您不想允许绑定。但是,如上所示,(Bind按钮的)bindBtn.setOnClickListener(new OnClickListener()的onClick()方法调用startService(backgroundService),导致出现此错误:“无法启动服务Intent { cmp=com.marie.mainactivity/.BackgroundService }:未找到”。
public class BackgroundService extends Service {
private NotificationManager notificationMgr;
@Override
public void onCreate() {
super.onCreate();
notificationMgr = NotificationManager)getSystemService(NOTIFICATION_SERVICE);
displayNotificationMessage("starting Background Service");
Thread thr = new Thread(null, new ServiceWorker(), "BackgroundService");
thr.start();
}
class ServiceWorker implements Runnable
{
public void run() {
// do background processing here...
//stop the service when done...
//BackgroundService.this.stopSelf();
}
}
@Override
public void onDestroy()
{
displayNotificationMessage("stopping Background Service");
super.onDestroy();
}
@Override
public void onStart(Intent intent, int startId) {
super.onStart(intent, startId);
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
private void displayNotificationMessage(String message)
{
Notification notification = new Notification(R.drawable.note, message, System.currentTimeMillis());
PendingIntent contentIntent = PendingIntent.getActivity(this, 0, new Intent(this, MainActivity.class), 0);
notification.setLatestEventInfo(this, "Background Service", message, contentIntent);
notificationMgr.notify(R.id.app_notification_id, notification);
}
}
我不理解这个例子的意义。如果onBind()返回null,那么有一个绑定按钮(bindBtn)有什么意义呢?我以为重点是展示如何启动BackgroundService。但是它似乎不起作用,除非我漏了什么。
我应该补充说明的是,我已经将以下内容添加到我的AndroidManifest.xml文件中:
<service android:name=".BackgroundService"></service>
as follows:
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<service android:name=".BackgroundService"></service>
</activity>
</application>