Due to the way that BackgroundAudio task and app lifecycle are built up, there doesn't seem to be a way to detect actual closing of the app and stopping its background task at this point.
This creates an odd situation for the user, where she can try to forcibly terminate the suspended-but-present app to "get rid" of the playing audio, yet the playback continues.
There is a possibility of reacting to the Suspending event, but that would just mean that the audio stops playing as soon as the user switches out of the app.
However, we are required to stop audio playback only when the user terminates the app via App Switch screen.
Is there any way of detecting that the app has been closed from its background task?
The BackgroundAudioTask is designed to continue even the main app has been terminated/suspended. There is no way to inform the BackgroundTask that the suspended app has been terminated.
After the app is suspended, no events are called or any code is run from your app. The last things what you can do is to put something into suspending event and/or window's events. You can save something in LocalSettings which will be inform the BackgroundTask that the app is inactive, it's also last chance to send a message to your task with information about UI status.
The above method is used in official MSDN sample.
Related
I used MediaCapture APIs in my App. Let's say I started recording and preview. During recording, I pressed Start key and quickly come back to the App by long pressing Back key and selecting my app (task swap). The result is that the preview is frozen either running on Emulator or 8.1 WP hardware. I don't find a better event to register for Start key. I understand that this.Resume can handle restoration when your APP is being deactivated. But here I mean I switch back from Start within 2~3 seconds and the Resume call is not get called. I am thinking that I can disable preview when Start key is pressed as a workaround. Then when App is brought back to foreground, user can restart recording. However, both scenarios I can't find a proper event. Of course if preview is not frozen when APP is swapped back, I don't need to do anything. Now it seems preview is not working after task swapped back from Start.
Here are the APIs I am using
_mediaCapture.StartRecordToStorageFileAsync(_profile, _recordStorageFile);
capturePreview.Source = App._mediaCapture;
_mediaCapture.StartPreviewAsync();
The issue you're hitting here has to do with the fact that as long as the debugger is attached, suspending/resuming won't work like it will once your app is running on its own.
See here: https://msdn.microsoft.com/en-us/library/windows/apps/hh974425.aspx
Try the same thing you're doing right now, except press the Suspend button in VS once your app is in the background. To bring it back, press the Resume button. Alternatively, try the same thing without the debugger attached.
As long as you're handling the Suspending/Resuming events correctly, MediaCapture lifecycle won't be a problem.
To learn more, have a look at the UniversalCameraSample on the Microsoft github repository: http://aka.ms/2015builduniversalcamerasample. It targets Windows 10, but a lot still applies to 8.1.
There are three events you can register for.
CoreWindow.Activated will be raised when you are no longer the foreground app. This can happen because the user switched away, or because something like a Reminder or Phone Call popped up on top, etc. Simply getting a toast notification does not raise the Activated event.
CoreWindow.VisibilityChanged will be raised when you are no longer visible. This happens when the user switches away, locks the phone, etc.
CoreApplication.Suspending will be raised when you are being suspended. The system doesn't suspend you immediately when the user switches away (in case they switch back quickly, eg they had accidentally hit the Start button). Instead it waits a few seconds before raising this event.
I currently have a Windows Phone app that connects to a SignalR service to receive notification data. The service pushes data to the phone, which the app accepts, process etc and it’s all working as expected.
However, I would like the app to continue to receive the notification data when the app is suspended and no longer in the foreground, and display the notification data as a toast message.
From what I can see, the Background Task infrastructure offers no way to do this.
I have access to a Suspending and Resuming event (using Prism) so here I could Register/Unregister my background task.
For the trigger, the only one that comes close to being relevant is the TimeTrigger, but this only has a freshness time of 15 minutes, so assuming I am recreating the connection in the background task, I would end up opening and then instantly closing the connection every 15 minutes which isn't what I want to do.
I could have an “infinite await” that just hangs until a timeout, but this doesn't feel like the right way to go (and the resource usage would be terrible).
Is there a way around this to achieve what I want to do?
No, Windows Phone apps cannot keep a channel open like this. If the goal is only for toasts then you can do the computation on the server and push a toast notification.
Windows Store apps can do this with the ControlChannelTrigger class, but it is not supported on Windows Phone.
When developing WP 8.1 Windows Runtime application, what’s the equivalent of the PhoneApplicationService.Activated and PhoneApplicationService.Deactivated events? It looks like PhoneApplicationService class is only available in Silverlight WP apps.
Application.Suspending event is not fired on Deactivated event (i.e. when I press Windows button).
You are right, under WinRT there is no Activated/Deactivated events. Your App can be Activated, but it's little different than in Silverlight. About the lifcycle you can read here at MSDN.
Your App will be Suspended just after you Navigate away from it. But - it's not working while you are debugging - more information here. When you run normally your App it will be suspended very fast after you hit Back/Start buttons.
About Navigation there is one thing you should be aware - when you Navigate away from the App, first OnNavigatedFrom is fired, then Suspended events (in the way you have subscribed them). But when you go back to your App - then Resuming events are fired, but OnNavigatedTo is not fired - reference:
Note On Windows Phone, OnNavigatedFrom() is called when the app is suspended. OnNavigatedTo() is not called when the app is resumed.
In some situations your App can be put into Not Running state. More again at Lifecycle at MSDN.
I recently received some code from another developer and there's one piece I would like to rework. It's a flash app that works with mic and webcam. When it is started you are prompted to press a button - after that the usual flash player settings windows appears asking you to allow access to mic and cam. The application needs to wait for user's response on this question. It was achieved in the code I received in a rather awkward fashion. Application progressed on mouse movement event, which would not be registered since the flash player settings popup block the area. Once it out of the way - any mouse move would make application to go on. I need to rework with in some better way, because this piece of code is also used in AIR application that doesn't ask for allowance and, therefore, if you click the opening button you would need to move your mouse in order to get things running. I believe there must be some decent way to notify the app that settings popup is gone. Could anyone advice on this?
The correct way to do this in Flash Player is to listen for StatusEvent.STATUS event which is dispatched after the user either allows or denies you access to their mic. See the documentation for Microphone.getMicrophone().
In AIR, however, you don't have to ask for user's permission to access their mic and camera, so this event is not dispatched when your application gets access to the input device. In that case, you can check through Capabilities.playerType property if your code is running in AIR and then proceed with doing what you would have done in response to receiving permission to access user's input devices.
So I understand that a foreground app can detect phone calls by registering for the obscured event, but while my app is running in the background, playing sound, sending notifications, etc, it does not hit the same event.
Is there a specific way to handle phone calls in this circumstance? The obscured event is the only one that I can find for detecting phone calls, but it won't work in this instance.
Unfortunately, with the current API there isn't...
In fact, I'd say that the obscured event can't even be considered a reliable way to detect an incoming phone call: you can use it right now for that purpose, but tomorrow Microsoft can just go ahead and add new stuff that will raise that very same event!