Develop Reference

UWP Start background task at startup

I just started learning UWP and i'm really confused on how it works. I already saw tens of posts that talk about my problem but can't figure out how to do what I want.
So I want to make an app that runs on windows startup, I want the app to be not visible so it needs a background Task, how can I trigger this background task without getting to the app UI ?
The app is supposed to have the Background Task always running, and its interface is supposed to be used as "settings" so I don't need the app to be shown on startup.
Thanks.

I found my way here after a lot of googling. to be honest I have come to the same conclusion as Motaz. But as of writing this I am way too invested in what I have already. While what I have here is not the perfect answer to his question. I wanted to come back and post what I've learned for anyone else who ends up here.
My need is a app that when started will monitor a third party USB device until the app is closed (regardless of whether the app is minimized or not)
Windows Template Studio is good, but the docs not so much. Especially when it comes to Background tasks.
I started here: https://github.com/Microsoft/Windows-universal-samples. But there is two problems.
They combined all the examples and some of the code is shared, which makes it difficult to pull a project out and hack it apart without breaking the original examples.
Following their background task example I perpetually had issue with the manifest and and it wanting an audio task
I went back to the template studio and created the simplest version with a background task possible. After a lot of trial and error I got something that works. I have posted it here: https://github.com/PillarOfSociety/WindowsTemplateStudio-BackgroundTask
Some things to note:
I am no expert on UWP and while this runs I have no intent on putting it in the store nor did I try.
If you do download my project and run it, you should be able to just hit the "Add events" and the "Start Back" button and the task should run and update the Progress bar.
I used an ApplicationTrigger. the original example from the template uses a TimeTrigger which takes time in MINUTES (took me too long to figure that out). Supposedly Application triggers have a 30sec timeout.. but on my laptop they live for much longer.. I don't know how long. This page is useful: https://learn.microsoft.com/en-us/windows/uwp/launch-resume/support-your-app-with-background-tasks
The template studio generated BackgroundTaskService will leave background tasks registered after the app is closed, but will NOT make the connection back to them once its rerun, so on a rerun either the task appears not to run, or will crash the app when triggered.
Important Code I discovered:
foreach (var task in BackgroundTaskRegistration.AllTasks)
{
TestText += task.Value.Name; //gets the typename of the task
//task.Value.Unregister(true); //will unregister tasks
}
await Task.CompletedTask;
The tasks in BackgroundTaskRegistration.AllTasks are not the BackgroundTask class that the template studio uses. IN my example I unregister all of them each time it runs so that you have a reference to the task as an instance of BackgroundTask.
Hopefully this helps someone and Good luck!

If you're just starting out use Windows Template Studio, it will be perfect for you. It is an extension of Visual Studio which lets you create new uwp projects with a lot of built in features, and you can only choose the features you want. It will save you a lot of time on basic stuff.
https://github.com/Microsoft/WindowsTemplateStudio

Call MediaCapture.InitializeAsync from UWP BackgroundTask

I am trying to take a photo during a BackgroundTask at an UWP application.
I read at documentation that InitializeAsync should be on the STA thread but is there some approach to achieve that from a MTA? I don't known, something like Dispatchers or others workarounds.
In my actual scenario, when I call CapturePhotoToStreamAsync just after the InitializeAsync, the following exception occurs:
System.Runtime.InteropServices.COMException (0xC00D3E82): A media
source cannot go from the stopped state to the paused state.
The funny thing is that it works if my app is not suspended.

I don't think you will get it to work in BackgroundTask - as MSDN says:
InitializeAsync should be called from the main UI thread of your app. For more information, see Guidelines for enabling sensitive devices.

Work while app is suspended in Windows Phone 8.1

I want to know what, how, and the limitations of the work that can be done whilst an app is suspended.
I'm not talking about Background Tasks, since those run whether the app is suspended or not, but what you can do while the app is in the background, suspended.
What I noticed so far is that if I have a BackgroundTask with the Completed event attached in the MainApp, that trigger is fired whilst the app is suspended, meaning that I can in fact do work in the MainApp, with the app suspended. So far I only have two ways of doing that, one is by using a BackgroundTask Completed event, and the other is by having a timer that forces something to happen.
However, what, how and the limitations of what I can do with the suspended app are not clear to me.
So, is there another way of working with a suspended app? And how much CPU time do I have, if limited, to work with?

I have played around a bit and found out that MessageWebSocket, if not disposed on app suspension, can still receive messages.
You could use the open socket connection to send messages, based on which you can execute code in the background.
A problem is when your app gets terminated by the OS (when the device does not have enough memory), then the socket connection will be closed too.
For more info on how to implement sockets see here.

You should check this link.
Understanding the App’s Lifecycle and Managing State - By Bob Tabor
Here its shown how you can manage to save the state of the app if your app is being suspended using suspension manager and also how to save data if the app is terminated from the suspension state.
Bob Tabor has clearly explained this in detail.
It was helpful to me, hope this helps you.

background task in windows phone 8.1

I am using a 3rd party rest api to query data and display it in my app. I have to perform a task like at night 12 approx. it will perform a background task to query data from rest api and update live tile and generate notification. I would like to use only C# only for this task. I don't know what will be best approach to do this task. But I using below code to perform background task to do this which is not working. Not sure why?
BackgroundTaskBuilder taskBuilder = new BackgroundTaskBuilder();
taskBuilder.Name = taskName;
SystemTrigger trigger = new SystemTrigger(SystemTriggerType.InternetAvailable, false);
taskBuilder.SetTrigger(trigger);
taskBuilder.AddCondition(new SystemCondition(SystemConditionType.InternetAvailable));
taskBuilder.TaskEntryPoint = typeof(BackgroundTask.BackgroundTask).FullName;
taskBuilder.Register();
and from background task I am querying data and generating toast notification.
Any help why this code is not working or when this task will fire. Is there any better approach to do above task?
Thanks

Regarding the code you have not working...
For Windows Phone 8.1 unlike Windows 8\8.1, you are required to call BackgroundExecutionManager.RequestAccessAsync() (search MSDN\internet) for ANY background task before registering task(s) whereas in Windows this is only required for some tasks. Make sure your code calls this and validate the returned value before registering your background task(s).
Regarding knowing if your task "worked"...
It's a good idea to have the background task implementation run (IBackgroundTask::Run()) independent of the trigger\conditions you've set to ensure it performs without issue by debugging it. See instructions in the following link: http://msdn.microsoft.com/en-US/library/windows/apps/xaml/jj542416.aspx.
Regarding your use of SystemConditionType.InternetAvailable...
I'm not 100% about this but I'm pretty certain this will be redundant given you already have a SystemTriggerType.InternetAvailable. I don't know of a situation where the trigger would fire but the condition wouldn't be true.
Regarding the requirement you've mentioned...
If I understand your requirement correctly you have different options here:
If your app is a Windows Phone XAML app that need to run based on time, I would recommend either TimeTrigger or MaintenanceTrigger triggers (as opposed to the SystemTrigger). These are both Background Tasks. For general info on Background Tasks and links to the TimeTrigger and MaintenanceTrigger documentation see this MSDN link: http://msdn.microsoft.com/en-US/library/windows/apps/xaml/hh977056.aspx.
If your app is a Windows Phone Silverlight 8.0 app you can use Background Agents, specifically either PeriodicTask or ResourceIntensiveTask. See the links posted by others or search the MSDN\internet for more info.
If your app is a Windows Phone Silverlight 8.1 app you can use the option in either 1 or 2 above.

I think you should try using PeriodicTask. Also consider the constraints mentioned in the link.

create one class with output Type :Windows Runtime Component
and put your Class that inheritance from IBackroundTask so this work
if you use from emulator for launching app, i think your app for register task not active in emulator.

Lync: VideoWindows of AVModality.VideoChannel are null after successfully calling BeginStart (COMException HRESULT: 0x80029C4A TYPE_E_CANTLOADLIBRARY)

We are currently trying to incorporate Lync communication (Lync SDK 2010) into our application and we have run into an issue with the VideoWindows (CaptureVideoWindow, RenderVideoWindow) of the AVModality's VideoChannel: They are always null, even after successfully calling BeginStart. The connection is definitely established. We can talk. Our own video is shown in a remote Lync client. AVModalityState is Connected. VideoChannelState goes from Connecting to Receive to Send.
It does not matter when and how we try to access them: Directly after BeginStart, in the AsyncCallback of BeginStart, in response to various state changes or in response to an external trigger (user click event); in the main/UI thread or in an event/callback thread. The two video windows are always null.
In the example application "%PROGRAMFILES%\Microsoft Lync\SDK\Samples\AudioVideoConversation", everything works as intended: As soon as BeginStart has finished, we can access the non-null video windows. In our little stand-alone prototype project, it works, too. But in our real application, it does not.
We have double checked everything and we have really run out of ideas of what might cause this problem.
Any ideas, any hints? Anything that we should be aware of?
(Link to corresponding MSDN forum thread)
Update (4th July 2012, 15:46 CET):
When we take a look at the members of the VideoChannel we find that internally a COMException occured in "Microsoft.Office.Uc": Error loading DLL, HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY). More details in the attached screenshot.
We did some research on this error, but found nothing that worked for us. Any ideas what causes the Exception?
Update (9th July 2012, 16:43 CET):
We did some further testing...
Our software consists of one main application and many plugin-like "apps" loaded via MEF. We created a minimal test app that makes a video call: The video windows did not work (as expected). But when we took the identical code and created a separate solution outside of our architecture, then it did work. So, it was an issue with the environment, not the code.
At first, we suspected MEF might be the problem. So, we hacked the lync code into our main application - circumventing the whole app architecture. Still not working.
Then we sliced off our whole system, bit by bit, until we finally reached a point where it did work. After following wrong tracks several times, we finally found the culprit... Quartz.NET!
For some strange reason the mere presence of an assembly reference to the Quartz.dll v.1.0.3.3, even without a single line of Quartz code, causes the video windows to not work. Unbelievable, but it's 100% reproducible: If we take the previously mentioned test solution and do nothing but add the reference, it stops working.
Any idea how such a thing is possible?

We solved it! Kind of. A reference to a Quartz.NET DLL somehow caused the issue. More details in the updated question.
For now, we have removed the component that used Quartz. We currently do not need it.
But I'm still interested in further input how a mere reference can cause such an issue.