Access library safely

TryAccessLibraryAsync.cs

private async Task<StorageLibrary> TryAccessLibraryAsync(KnownLibraryId library)
{
    try
    {
        return await StorageLibrary.GetLibraryAsync(library);
    }
    catch (UnauthorizedAccessException)
    {
        //explain the issue
        MessageDialog requestPermissionDialog =
            new MessageDialog(
                      $"The app needs to access the {library}. " +
                       "Press OK to open system settings and give this app permission. " +
                       "If the app closes, reopen it afterwards. " +
                       "If you Cancel, the app will have limited functionality only.");
        var okCommand = new UICommand("OK");
        requestPermissionDialog.Commands.Add(okCommand);
        var cancelCommand = new UICommand("Cancel");
        requestPermissionDialog.Commands.Add(cancelCommand);
        requestPermissionDialog.DefaultCommandIndex = 0;
        requestPermissionDialog.CancelCommandIndex = 1;

        var requestPermissionResult = await requestPermissionDialog.ShowAsync();
        if (requestPermissionResult == cancelCommand)
        {
            //user chose to Cancel, app will not have permission
            return null;
        }

        //open app settings to allow users to give us permission
        await Launcher.LaunchUriAsync(new Uri("ms-settings:appsfeatures-app"));

        //confirmation dialog to retry
        var confirmationDialog = new MessageDialog(
                   $"Please give this app the {library} permission " +
                    "in the Settings app which has now opened.");
        confirmationDialog.Commands.Add(okCommand);
        await confirmationDialog.ShowAsync();                
    }
    return null;
}