When we are developing a Windows Store app, we may need to do something even if our application is suspended or closed; such as updating our live tile, showing a tile notification, syncing data or performing another specific action. Since Windows 8 is an operating system that emphasizes on power saving, we are not allowed to keep our application working in the background. Therefore, to have this functionality Windows 8 supports a background task system which allows us to define a background task (basically, our own lines of code) that will be executed periodically or when certain conditions are met. An example for this would be the Store application on the start screen, which periodically checks if there are updates to our installed apps, but does so when we have an internet connection.
Before moving on to developing our application, there are a few key points we need to know about background tasks. Background tasks have CPU and network constraints, we can not execute code that takes a long time to complete in our background tasks. The network constraint is active only when the device is on battery, and it is not calculated in terms of bandwidth but the amount of battery used by the connection. The limits of these constraints change depending on the type of the background task used.
If it is an application that needs to be frequently updated (such as a mail or VOIP app), the app will need to placed on the lockscreen but the background task will have a more relaxed resource management (2 seconds of CPU time). The catch is that the maximum number of apps that can be on the lockscreen at the same time is 7, so your user will need to add your app to the lockscreen in order your background task to work. If the application does not need to be updated that frequently, however, we can use a maintenance task, which doesn’t require the app to be on lockscreen and will be triggered based on certain conditions, but has a more restrict resource management (1 second of CPU time).