Long Running Task Sample App

This sample application demonstrates how to implement a long running task in Xamarin.Forms for both iOS and Android platforms. The app utilizes a service injected into the Xamarin.Forms project to run a counter even when the app is in the background.

Inputs

The application responds to two messages sent via the MessagingCenter:

• StartLongRunningTaskMessage: Initiates the long-running task. This message is typically sent when the user presses the "Start" button on the main page.
• StopLongRunningTaskMessage: Stops the long-running task. This message is usually sent when the user interacts with the "Stop" button on the main page.

Outputs

The application updates the UI with the current counter value via the MessagingCenter:

• UpdateUICounter: Sends the current counter value to the main page, allowing the UI to be updated. This is done on the main thread using Device.BeginInvokeOnMainThread to avoid threading issues.

Additionally, a CancelledMessage is sent through the MessagingCenter if the task is cancelled, either by the user or by the operating system.

Usage

1. Start the task: The user presses the "Start" button. This sends a StartLongRunningTaskMessage through the MessagingCenter. The platform-specific code (either Android or iOS) receives this message and starts a background service or task that runs the counter.
2. Update the UI: The background task periodically increments a counter and sends the updated value to the main page using the UpdateUICounter message. The main page receives this message and updates a label to display the counter value.
3. Stop the task: The user presses the "Stop" button, sending a StopLongRunningTaskMessage message, which stops the background service or task.
4. Cancellation: If the task is cancelled, a CancelledMessage is sent to the main page.

Implementation Details

• The counter logic is implemented in a shared CounterService class that implements the IService interface.
• The background task is managed by platform-specific code:
  • Android: Utilizes a background service (DroidLongRunningTaskCounter).
  • iOS: Uses a background task (iOSLongRunningTaskCounter).
• The platform-specific code invokes a shared LongrunningTimerTask class which handles the main loop of the counter and sends updates to the UI.
• Cancellation is handled using a CancellationTokenSource.

This application provides a simple example of how to run long-running tasks in Xamarin.Forms. It can be adapted for a variety of use cases where background processing is required, such as data synchronization, file uploads, or location tracking.