Wait for an event in a WaterfallDialog

Working on a Skill, I needed to block the execution of a WaterfallDialog while waiting for a specific event to arrive.
The solution is simple and based on the use of EventPrompt. Below I show how to use it.

Register EventPrompt in the constructor

AddDialog(new WaterfallDialog(nameof(WaterfallDialog), new WaterfallStep[]
{
	HelloAsync,
	WaitForEventAsync,
	DoneAsync
}));

AddDialog(new EventPrompt(nameof(EventPrompt), "SampleEvent", Validate));

InitialDialogId = nameof(WaterfallDialog);

Implement the three dialog steps

private async Task<DialogTurnResult> HelloAsync(WaterfallStepContext stepContext, CancellationToken cancellationToken)
{
	await stepContext.Context.SendActivityAsync(MessageFactory.Text("Hello :)"), cancellationToken);

	return await stepContext.NextAsync(cancellationToken);
}

private async Task<DialogTurnResult> WaitForEventAsync(WaterfallStepContext stepContext, CancellationToken cancellationToken)
{
	return await stepContext.PromptAsync(nameof(EventPrompt), new PromptOptions { Prompt = MessageFactory.Text("Waiting for the event") });
}

private async Task<DialogTurnResult> DoneAsync(WaterfallStepContext stepContext, CancellationToken cancellationToken)
{
	await stepContext.Context.SendActivityAsync(MessageFactory.Text("After I receive the event."), cancellationToken);

	return await stepContext.NextAsync(cancellationToken);
}

Implement the event validator

async Task<bool> Validate(PromptValidatorContext<Activity> promptContext, CancellationToken cancellationToken)
{
	var activity = promptContext.Recognized.Value;
	if (activity.Type == ActivityTypes.Event)
	{
		try
		{
			string eventValue = (string)activity.Value;
			
			if(eventValue == "OK")
			{
				return true;
			}
		}
		catch { }
	}

	return false;
}