Handling flow from Prompt Validators

Creating a basic flow with Botframework V4 is pretty straightforward. You define your steps and any other dialogs or prompts that you may wish to use. For example, consider this basic name capturing definition;

Add(Inputs.Text, new Microsoft.Bot.Builder.Dialogs.TextPrompt(TextValidator));
Add(Name, new WaterfallStep[]
{
    // Each step takes in a dialog context, arguments, and the next delegate.
    async (dc, args, next) =>
    {
        // Prompt for the user's first name.
        await dc.Prompt(Inputs.Text, "Hey, what's your first name?");
    },
    async (dc, args, next) =>
    {
        dc.ActiveDialog.State["1stName"] = args["Text"].ToString();
     
        // Prompt for the user's second name.
        await dc.Prompt(Inputs.Text, "what's your second name?");
    },
...
private Task TextValidator(ITurnContext context, TextResult toValidate)
{
    if (toValidate.Text == ".")
    {
        toValidate.Status = null;

    }
    
    return Task.CompletedTask;
}

The above code will reject the second name if the user types in a full-stop. But what will happen next needs to be considered. The current code will correctly reject the full-stop but it will restart the dialog and ask the user for their first name again. There are a couple of ways to handle this, and they can be implemented in unison.

Use a Retry Message

When a prompt has a Retry-Message associated with it then any failure from the Validator will keep the user on the same waterfall step.

...
 async (dc, args, next) =>
    {     
        dc.ActiveDialog.State["1stName"] = args["Text"].ToString();
        // Prompt for the user's second name.
        await dc.Prompt(Inputs.Text, "what's your second name?", 
            new PromptOptions
            {
                RetryPromptString = "what's your really your second name?"
            });
    },
...

The above code is probably all your need, but you may also want to equip your waterfall steps to be more…re-entrant.

Replay dialog

This is particularly useful if you provide a way to edit the user’s choices. The idea is that each step examines its arguments or state and if already fulfilled simply passes the flow onto the next step. In the final step you decide if everything has completed or if the flow should start again.
Example step;

async (dc, args, next) =>
    {
        if (args.ContainsKey("1stStep")
        {
          await next(args);
        }
        else
        {
          // Prompt for the user's first name.
          await dc.Prompt(Inputs.Text, "Hey, what's your first name?");
        }
    },
...

Final step;

async (dc, args, next) =>
    {
        if (AllConditionsMet(args))
        {
          // finish the dialog
          await dc.End(dc.ActiveDialog.State);
        }
        else
        {
          // replay the flow
          await dc.Replace("yourdialogName", dc.ActiveDialog.State);
        }
    },

Combining Retry and Replay

There is nothing stopping you using a combination of the methods. If you want to enable an editing scenario but want the framework to ensure a criteria is met for specific steps then just implement both.

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