[Question] .NET 9 MAUI sample app with sample content async lock for DisplayAlert (why?)

[janseris]

Hi, I noticed the new VS project template for MAUI for .NET 9 has the following code:

Why is async lock (SemaphoreSlim) used here for Shell.DisplayAlert?

/// <summary>
/// Modal Error Handler.
/// </summary>
public class ModalErrorHandler : IErrorHandler
{
    SemaphoreSlim _semaphore = new(1, 1);

    /// <summary>
    /// Handle error in UI.
    /// </summary>
    /// <param name="ex">Exception.</param>
    public void HandleError(Exception ex)
    {
        DisplayAlert(ex).FireAndForgetSafeAsync();
    }

    async Task DisplayAlert(Exception ex)
    {
        try
        {
            await _semaphore.WaitAsync();
            if (Shell.Current is Shell shell)
                await shell.DisplayAlert("Error", ex.Message, "OK");
        }
        finally
        {
            _semaphore.Release();
        }
    }
}

Thanks

[TommiGustafsson-HMP]

Quite obviously the semaphore is there to prevent several alerts from displaying at the same time. So, now it waits that the previous one is closed first before displaying the next one.