Send a local app notification from a C# app

First, in your Package.appxmanifest, add:

1. Declaration for xmlns:com
2. Declaration for xmlns:desktop
3. In the IgnorableNamespaces attribute, com and desktop
4. desktop:Extension for windows.toastNotificationActivation to declare your toast activator CLSID (using a new GUID of your choice).
5. MSIX only: com:Extension for the COM activator using the GUID from step #4. Be sure to include the Arguments="-ToastActivated" so that you know your launch was from a notification

Package.appxmanifest

<!--Add these namespaces-->
<Package
  ...
  xmlns:com="http://schemas.microsoft.com/appx/manifest/com/windows10"
  xmlns:desktop="http://schemas.microsoft.com/appx/manifest/desktop/windows10"
  IgnorableNamespaces="... com desktop">
  ...
  <Applications>
    <Application>
      ...
      <Extensions>

        <!--Specify which CLSID to activate when toast clicked-->
        <desktop:Extension Category="windows.toastNotificationActivation">
          <desktop:ToastNotificationActivation ToastActivatorCLSID="replaced-with-your-guid-C173E6ADF0C3" /> 
        </desktop:Extension>

        <!--Register COM CLSID LocalServer32 registry key-->
        <com:Extension Category="windows.comServer">
          <com:ComServer>
            <com:ExeServer Executable="YourProject\YourProject.exe" Arguments="-ToastActivated" DisplayName="Toast activator">
              <com:Class Id="replaced-with-your-guid-C173E6ADF0C3" DisplayName="Toast activator"/>
            </com:ExeServer>
          </com:ComServer>
        </com:Extension>

      </Extensions>
    </Application>
  </Applications>
 </Package>

Then, in your app's startup code (App.xaml.cs OnStartup for WPF), subscribe to the OnActivated event.

// Listen to notification activation
ToastNotificationManagerCompat.OnActivated += toastArgs =>
{
    // Obtain the arguments from the notification
    ToastArguments args = ToastArguments.Parse(toastArgs.Argument);

    // Obtain any user input (text boxes, menu selections) from the notification
    ValueSet userInput = toastArgs.UserInput;

    // Need to dispatch to UI thread if performing UI operations
    Application.Current.Dispatcher.Invoke(delegate
    {
        // TODO: Show the corresponding content
        MessageBox.Show("Toast activated. Args: " + toastArgs.Argument);
    });
};

When the user clicks any of your notifications (or a button on the notification), the following will happen...

If your app is currently running...

1. The ToastNotificationManagerCompat.OnActivated event will be invoked on a background thread.

If your app is currently closed...

1. Your app's EXE will be launched and ToastNotificationManagerCompat.WasCurrentProcessToastActivated() will return true to indicate the process was started due to a modern activation and that the event handler will soon be invoked.
2. Then, the ToastNotificationManagerCompat.OnActivated event will be invoked on a background thread.

When the user clicks any of your notifications (or a button on the notification), the following will happen...

If your app is currently running...

1. The ToastNotificationManagerCompat.OnActivated event will be invoked on a background thread.

If your app is currently closed...

1. Your app's EXE will be launched and ToastNotificationManagerCompat.WasCurrentProcessToastActivated() will return true to indicate the process was started due to a modern activation and that the event handler will soon be invoked.
2. Then, the ToastNotificationManagerCompat.OnActivated event will be invoked on a background thread.

In your app's startup code (App.xaml.cs OnStartup for WPF), subscribe to the OnActivated event.

// Listen to notification activation
ToastNotificationManagerCompat.OnActivated += toastArgs =>
{
    // Obtain the arguments from the notification
    ToastArguments args = ToastArguments.Parse(toastArgs.Argument);

    // Obtain any user input (text boxes, menu selections) from the notification
    ValueSet userInput = toastArgs.UserInput;

    // Need to dispatch to UI thread if performing UI operations
    Application.Current.Dispatcher.Invoke(delegate
    {
        // TODO: Show the corresponding content
        MessageBox.Show("Toast activated. Args: " + toastArgs.Argument);
    });
};

When the user clicks your notification (or a button on the notification with foreground activation), your app's App.xaml.cs OnActivated will be invoked, and the arguments you added will be returned.

App.xaml.cs

protected override void OnActivated(IActivatedEventArgs e)
{
    // Handle notification activation
    if (e is ToastNotificationActivatedEventArgs toastActivationArgs)
    {
        // Obtain the arguments from the notification
        ToastArguments args = ToastArguments.Parse(toastActivationArgs.Argument);

        // Obtain any user input (text boxes, menu selections) from the notification
        ValueSet userInput = toastActivationArgs.UserInput;
 
        // TODO: Show the corresponding content
    }
}

You don't need to do anything! When MSIX apps are uninstalled, all notifications and any other related resources are automatically cleaned up.

If your app has an uninstaller, in your uninstaller you should call ToastNotificationManagerCompat.Uninstall();. If your app is a "portable app" without an installer, consider calling this method upon app exit unless you have notifications that are meant to persist after your app is closed.

The uninstall method will clean up any scheduled and current notifications, remove any associated registry values, and remove any associated temporary files that were created by the library.

You don't need to do anything! When UWP apps are uninstalled, all notifications and any other related resources are automatically cleaned up.

For desktop applications, background activations are handled the same as foreground activations (your OnActivated event handler will be triggered). You can choose to not show any UI and close your app after handling activation.

When you specify background activation on your app notification (or on a button inside the notification), your background task will be executed instead of activating your foreground app.

For more information on background tasks, please see Support your app with background tasks.

If you are targeting build 14393 or later, you can use in-process background tasks, which greatly simplify things. Note that in-process background tasks will fail to run on older versions of Windows. We'll use an in-process background task in this code sample.

const string taskName = "ToastBackgroundTask";

// If background task is already registered, do nothing
if (BackgroundTaskRegistration.AllTasks.Any(i => i.Value.Name.Equals(taskName)))
    return;

// Otherwise request access
BackgroundAccessStatus status = await BackgroundExecutionManager.RequestAccessAsync();

// Create the background task
BackgroundTaskBuilder builder = new BackgroundTaskBuilder()
{
    Name = taskName
};

// Assign the toast action trigger
builder.SetTrigger(new ToastNotificationActionTrigger());

// And register the task
BackgroundTaskRegistration registration = builder.Register();

Then in your App.xaml.cs, override the OnBackgroundActivated method. You can then retrieve the pre-defined arguments and user input, similar to the foreground activation.

App.xaml.cs

protected override async void OnBackgroundActivated(BackgroundActivatedEventArgs args)
{
    var deferral = args.TaskInstance.GetDeferral();
 
    switch (args.TaskInstance.Task.Name)
    {
        case "ToastBackgroundTask":
            var details = args.TaskInstance.TriggerDetails as ToastNotificationActionTriggerDetail;
            if (details != null)
            {
                ToastArguments arguments = ToastArguments.Parse(details.Argument);
                var userInput = details.UserInput;

                // Perform tasks
            }
            break;
    }
 
    deferral.Complete();
}