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<TextBox TextChanging="TextBox_OnTextChanging" />

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private void TextBox_OnTextChanging(TextBox sender, TextBoxTextChangingEventArgs args)
{
    sender.Text = new String(sender.Text.Where(char.IsDigit).ToArray());
}

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var library = await StorageLibrary.GetLibraryAsync(KnownLibraryId.Pictures);

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private async Task<StorageLibrary> TryAccessLibraryAsync(KnownLibraryId library)
{
    try
    {
        return await StorageLibrary.GetLibraryAsync(library);
    }
    catch (UnauthorizedAccessException)
    {
       ...
    }

MartinZikmund

//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.");

//setup dialog commands
var okCommand = new UICommand("OK");
requestPermissionDialog.Commands.Add(okCommand);

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

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//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();     

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private async Task<StorageLibrary> TryAccessLibraryAsync(KnownLibraryId library)
{
    try
    {
        return await StorageLibrary.GetLibraryAsync(library);
    }
    catch (UnauthorizedAccessException)
    {
        //explain the issue
        MessageDialog requestPermissionDialog =

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var userManager = (UserManager)GetSystemService(UserService);
if (userManager.IsUserAGoat)
{
    //🐐
}

MartinZikmund

if (ActivityManager.IsUserAMonkey)
{
    //🐒🐵🙊🙉🙈
}