Multitasking and Triggered Background Processing in Windows Phone 8.1

Editor's Notes

• #5: Anytime app is running code while not in foreground Great way to enhance user experience, get users to interact with your app
• #6: History of Multitasking in Windows Phone 7 & 8
• #7: Windows Phone 7 didn’t really have multitasking Windows Phone 8 added new mechanisms to provide content when not in the foreground app Live tiles or toasts – triggered by push notifications or scheduled OS Brokered tasks like background downloads Background tasks and agents which would run periodically
• #8: In WP8 we had PeriodicTasks and ResourceIntensiveTasks which would run periodically every half hour or so. Could be used to download new content for the user, update tiles, etc. Background Transfer Service allowed you to download large files while not in the foreground Background location tracking is a special exception for navigation apps like CoPilot. As long as these apps are still actively using the GPS they would be allowed to continue running while not in the foreground. VOIP and Audio Agents were another special case of background execution for apps like Skype or Pandora.
• #10: The new Windows Runtime Background execution model is centered around Background Tasks. Rather then running periodically they respond to triggers or conditions. This is a converged API, so it’s the same background tasks that are available for Windows Apps. Because it’s a converged API you do need to request access to run in the background.. On Windows this would display a popup, but on Windows Phone there’s no UI. You still need to check though, and there are certain conditions that would cause background access to not be granted, such as if the user disabled your app through the battery saver settings.
• #11: Here are some of the different triggers available. If you’ve done any development with Windows Store apps these may be familiar because it is a converged API. Go over System Triggers TimeTrigger run task on an interval, must specify atleast a 30 minute intervals, but on windows phone interval will usually be no less then half an hour. Maintenance Trigger similar to the resource intensive task, run resource intensive code when the phone is plugged in
• #12: Demo Time Demo in WP8.1 Silverlight, all of the new multitasking features for Windows Universal Apps are also available for Windows Phone Silverlight 8.1 Registering background task in C# Display available memory in C# toast At Build all the sessions I went to about background tasks told us that we should be writing our background task code in C++. Background tasks have a limited amount of memory resources available to them ~16MB, by not loading up the CLR you can save a few MBs and hopefully avoid Out of Memory exceptions. You can still write your apps in C#, but the nice thing about the Windows Runtime is that you can interoperate between C#, C++ and even WinJS really easily. Convert C# Background Task into a C++ project Modify code and manifest to register C++ background task
• #13: All of the tasks I’ve showed you so far were already there for Windows Store, so now we’ll go into some new forms of multitasking
• #14: All this is available for Silverlight 8.1. So if you’re already invested with apps developed in Windows Phone 8, like I am. Then you can still benefit from all these new background tasks without having to migrate to the Windows Univeral App Model. When you upgrade to 8.1 your 8.0 style background agents will be hosted on top of the modern background infrastructure and should run better with the newer resource management. Note that you should make sure you don’t have a mix of 8.0 BG Agents and 8.1 BG Tasks as conflicts will occur with mixing the Silverlight CLR and WinRT CLR. If you write your BG Agent/Task code in C++ though you’ll be fine.
• #15: Not a Bluetooth expert so I don’t have a demo to show about any of the new Bluetooth functionality here, but I’m really excited about it. Bluetooth LE is a new feature for Windows Phone 8.1 it should be available in many of the newer phones, Lumia Icon, 930, 1520 and 630. Bluetooth triggers are based on existing WinRT Bluetooth APIs DeviceChange is pretty self explanatory if a Device connects or reconnects to the phone this trigger will be raised DeviceUpdate trigger is going to be core to how fitness apps like FitBit could integrate with Windows Phone. With these you’ll be able to have a long running background task that communicates with Bluetooth LE devices like heart rate monitors or pedometers
• #16: You can now have your app setup a Windows Notification Service channel and associate it with a background task Then any raw push notifications that come through on that channel will activate the background task. This can be really useful for news reader applications or social media like twitter or facebook. I know one thing that frustrates me with twitter is that I’ll see a notification come through from twitter, and click on it to activate the app. When I go into the app though it still needs to connect to the service and fetch the new tweets. With these new background tasks that handle RAW notifications a service like twitter could get the notification, connect to the service to refresh content and THEN show a toast notification to let me know that someone mentioned me. It’ll make the app appear more responsive to me, even though in reality I’m getting my toast notification a second or two later.
• #21: One of the things done most frequently with periodic tasks in WP8.0 was updating tiles. A lot of developers would take some XAML, render it to a bitmap and then update a tile with that bitmap. If you’ve done any development on Windows 8 you might know that this wasn’t possible with Windows 8 background tasks. It’s not possible to access the XAML tree there. So a new type of background task is available for Windows Phone that gives access to the XAML visual tree. So in this background task you’ll basically create some XAML, use RenderTargetBitmap to render the XAML to a PNG and then you can use that PNG to update your tile
• #22: So the interesting thing about this demo is that Microsoft wants you to use C++ for XamlRenderingBackgroundTasks so much that they didn’t make a C# version of the sample code. But when working on this presentation I was curious about what the memory savings would look like in a more complex demo like this, so I converted the C++ task into a C# one to compare them.