//public abstract void DateTimePrompt(DateTimePromptConfig config);
 //public abstract void DurationPrompt(DurationPromptConfig config);
 public abstract void Prompt(PromptConfig config);
 public static Task<PromptResult> PromptAsync(this IUserDialogService dialogs, PromptConfig config) {
     var tcs = new TaskCompletionSource<PromptResult>();
     config.OnResult = tcs.SetResult;
     dialogs.Prompt(config);
     return tcs.Task;
 }