On Windows 8, a call to “await aMessageDialog.ShowAsync()” can only be made once, otherwise System.UnauthorizedAccessException will be thrown (E_ACCESSDENIED 80070005). This is a helper method to display dialogs although it’s not thread-safe. It’s inspired on StackOverflow answers:

public static class DialogDisplayer {
    private static IAsyncOperation currentlyShownDialog;

    public static async Task TryToShowDialog(MessageDialog messageDialog){
            await WaitForUIThreadToBeReady();
            await ShowDialog(messageDialog);
        catch (TimeoutException ex){
            //Logger.Information("Time out waiting for a MessageDialog to be closed");
        catch (TaskCanceledException ex){
        catch (UnauthorizedAccessException ex){
            //Logger.Information("Multiple dialogs are being opened at the same time. There is a direct call to ShowAsync somewhere. Instead of using ShowAsync, use this method");

    private static void CancelDialog(){
        currentlyShownDialog = null;

    private static void RequestPreviousDialogCancelation(){
        if (IsThereAnyOpenedDialog()){

    private static async Task ShowDialog(MessageDialog messageDialog){
        currentlyShownDialog = messageDialog.ShowAsync();
        await currentlyShownDialog;

    private static async Task WaitForUIThreadToBeReady(){
        var attempts = 0;
        while (IsThereAnyOpenedDialog()){
            await Task.Delay(TimeSpan.FromMilliseconds(100));
            if (attempts > 5){
                throw new TimeoutException();

    private static bool IsThereAnyOpenedDialog(){
       return currentlyShownDialog != null && currentlyShownDialog.Status == AsyncStatus.Started;


var messageDialog = new MessageDialog("Hello world");
await DialogDisplayer.TryToShowDialog(messageDialog);