练习的重点是：保持服务活着，将它从一个活动传递到另一个活动。
- Activity A 在服务 S 上调用 bindService()；
- S.onBound() 调用；
- A.serviceConnection.onServiceConnected() 被调用；
- 活动 A 开始活动 B；
- Activity B 在服务 S 上调用 bindService()；
- B.serviceConnection.onServiceConnected() 被调用；5a：从 onServiceConnected() 活动 B 调用 A.finish()；
- 活动 A 正在停止，从其 onDestroy() 方法调用 unbindService(S)。
预期行为：服务 S 继续愉快地存在，直到活动 B 调用 unbindService()
实际行为：
- S.onUnbind() 被调用；
- S.onDestroy() 被调用；
- B.serviceConnection.onServiceDisconnected() 被调用；
从而破坏了链接并与文档相矛盾。
为什么？我错过了什么？
更新：已解决。来自http://developer.android.com/reference/android/app/Service.html：
服务既可以启动，也可以绑定连接。在这种情况下，只要服务已启动或与 Context.BIND_AUTO_CREATE 标志有一个或多个连接，系统就会保持服务运行。
这是代码：
public class A extends Activity {
private final Logger logger = LoggerFactory.getLogger(getClass().getSimpleName());
private String serviceClassName;
private ServiceConnection feedConnection;
private Messenger feedMessenger;
private void bind(String argument) {
serviceClassName = TheService.class.getName();
Intent intent = new Intent(serviceClassName);
intent.putExtra(Keys.ACCOUNT, argument);
feedConnection = new FeedConnection();
if (!bindService(intent, feedConnection, Context.BIND_AUTO_CREATE)) {
throw new IllegalStateException("Failed to bind to " + argument);
}
logger.debug("bindService(" + serviceClassName + ") successful");
}
private void forward() {
Intent intentB = new Intent();
intentB.setClassName(B.class.getPackage().getName(), B.class.getName());
intentB.putExtra(Keys.SERVICE_CLASS_NAME, serviceClassName);
startActivity(intentB);
}
@Override
protected void onDestroy() {
super.onDestroy();
unbindService(feedConnection);
}
private class FeedConnection implements ServiceConnection {
@Override
public void onServiceConnected(ComponentName className, IBinder service) {
A.this.feedMessenger = new Messenger(service);
}
@Override
public void onServiceDisconnected(ComponentName className) {
A.this.feedMessenger = null;
logger.error("Crashed " + Integer.toHexString(hashCode()));
}
}
}
public class B extends Activity {
private final Logger logger = LoggerFactory.getLogger(getClass().getSimpleName());
private ServiceConnection feedConnection;
private Messenger feedMessenger;
private A activityA;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
bindFeed();
}
private void bindFeed() {
Intent startingIntent = getIntent();
String serviceClassName = startingIntent.getStringExtra(Keys.SERVICE_CLASS_NAME);
Intent intent = new Intent(serviceClassName);
feedConnection = new FeedConnection();
// FIXME: BIND_AUTO_CREATE flag is missing
if (!bindService(intent, feedConnection, 0)) {
throw new IllegalStateException("Failed to bind to " + serviceClassName);
}
logger.debug("bindService(" + serviceClassName + ") successful");
}
private class FeedConnection implements ServiceConnection {
@Override
public void onServiceConnected(ComponentName className, IBinder service) {
B.this.feedMessenger = new Messenger(service);
logger.debug("bound " + className);
// Finish the previous activity only after the service is bound
activityA.fileList();
}
@Override
public void onServiceDisconnected(ComponentName className) {
B.this.feedMessenger = null;
logger.error("Crashed " + className);
}
}
}