bindService()返回false但需要调用unbindService()？

Question

我的应用使用其他(我的)应用提供的服务.我使用的绑定的服务机智Messenger访问和与它(和,因为它是一个不同的应用程序,它也是一个远程服务)进行通信.

当我打电话bindService了适当的意图,并调用返回false(如当APK提供服务不在身边预期),我从文档和示例代码假设,那我就不需要unbind了ServiceConnection.但是,当我在我的Galaxy Nexus(Jelly Bean)设备上这样做时,我ServiceConnectionLeaked在完成时得到了众所周知的信息Activity.

我通过这样做来挽救这一点

if (!ctxt.bindService(intent, serviceConnection, Context.BIND_AUTO_CREATE)) {
    try { 
        ctxt.unbindService(serviceConnection);
    } catch (Throwable t) {}
    // Clean up 
    return;
}
// Store serviceConnection for future use

我很好奇:我是否只是遗漏了文档中的内容,是否应该以这种方式工作？我添加了try ... catch以确保即使此行为在其他设备或Android版本上确实不同,我的应用程序也不会(负面)受其影响.

Answer 1

一般来说,无论bindService()call是返回true还是false ,都始终由框架分配和注册ServiceConnection .请参阅android.app.ContextImpl中的 bindService()实现:

public boolean bindService(Intent service, ServiceConnection conn, int flags, int userHandle) {
    IServiceConnection sd;
    if (conn == null) {
        throw new IllegalArgumentException("connection is null");
    }
    if (mPackageInfo != null) {
        // A new ServiceDispatcher will be created and registered along with 
        // ServiceConnection in LoadedApk.mService for your application context.
        sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
                mMainThread.getHandler(), flags);
    } else {
        throw new RuntimeException("Not supported in system context");
    }
    try {
        ... ...
        return res != 0;
    } catch (RemoteException e) {
        return false;
    }
}

根据官方开发指南的建议,您应该在完成服务后解除绑定,这是一种很好的编程方式:

• 要断开与服务的连接,请调用unbindService().

  当您的客户端被销毁时,它将与服务解除绑定,但是当您完成与服务的交互或您的活动暂停时,您应始终取消绑定,以便服务可以在未使用时关闭.(下面将讨论绑定和解除绑定的适当时间.)

当框架开始执行最终清理(例如,当您的应用程序退出时)并发现存在未注册的ServiceConnection时,将引发ServiceConnectionLeaked,然后框架将尝试为您取消绑定.请参阅android.app.LoadedApk中的 removeContextRegistrations()实现:

public void removeContextRegistrations(Context context,
        String who, String what) {
    final boolean reportRegistrationLeaks = StrictMode.vmRegistrationLeaksEnabled();
    ... ...
    //Slog.i(TAG, "Receiver registrations: " + mReceivers);
    HashMap<ServiceConnection, LoadedApk.ServiceDispatcher> smap =
        mServices.remove(context);
    if (smap != null) {
        Iterator<LoadedApk.ServiceDispatcher> it = smap.values().iterator();
        while (it.hasNext()) {
            LoadedApk.ServiceDispatcher sd = it.next();
            ServiceConnectionLeaked leak = new ServiceConnectionLeaked(
                    what + " " + who + " has leaked ServiceConnection "
                    + sd.getServiceConnection() + " that was originally bound here");
            leak.setStackTrace(sd.getLocation().getStackTrace());
            Slog.e(ActivityThread.TAG, leak.getMessage(), leak);
            if (reportRegistrationLeaks) {
                StrictMode.onServiceConnectionLeaked(leak);
            }
            try {
                ActivityManagerNative.getDefault().unbindService(
                        sd.getIServiceConnection());
            } catch (RemoteException e) {
                // system crashed, nothing we can do
            }
            sd.doForget();
        }
    }
    mUnboundServices.remove(context);
    //Slog.i(TAG, "Service registrations: " + mServices);
}