Unable to cast object of type ‘System.String’ to type ‘AuthBotES.ReturnIntents’ - botframework

Question

Currently I had integrate LUIS with Bot Framework v4.
When I search for result match with Intent,
the Bot return me with this Error:
Error : Unable to cast object of type ‘System.String’ to type ‘AuthBotES.ReturnIntents’.
My Source code as below:
if (stepContext.Result != null)
{
var result = (ReturnIntents)stepContext.Result;
var msg = $"{result}";
await stepContext.Context.SendActivityAsync(MessageFactory.Text(msg), cancellationToken);
}
and my ReturnIntents classes.
public class ReturnIntents
{
public string Intent { get; set; }
public double Score { get; set; }
public string Entities { get; set; }
}

Answer 1

A few issues here:
The first code block you posted looks to be for handling the result of a dialog, not for processing a LUIS result.
The cast from string to ReturnIntents will always fail.
Even if your cast of stepContext.Result to ReturnIntents did work, your msg variable would only contain namespace.to.class.ReturnIntents (the string representation of the object type, not the string representation of the objects properties.
Your msg variable is redundant.
I will address these in the order that they occur.
1 - Incorrect code block
This block of code looks suspiciously like code used to process a dialog and here e.g.:
var result = (bool)stepContext.Result;
Rather than the code for handling a LUIS result e.g.:
var dispatchResult = await cognitiveModels.DispatchService.RecognizeAsync(dc.Context, CancellationToken.None);
2 - Casting error
The error is telling you that it doesn't know how to convert a string object to a ReturnIntents object. To convert the string to your object you could use a couple of methods:
Use the NewtonSoft.Json NuGet package to allow you to turn the JSON string into your object as explained here.
2) A user defined type conversion as detailed in the official docs here and explained in this answer.
This error is a red herring in terms of your solution because I believe you're accidentally copied in the wrong block of code.
3 - Incorrect ToString behaviour
To get the string value of a ReturnIntents you will need to override the ToString method for the class and write your own custom implementation.
4 - Redundant cast
This:
// We know that this cast fails, and that stepContext.Result is a string
var result = (ReturnIntents)stepContext.Result;
// This will only return <namespace.path>.ReturnIntents (if the cast above works)
var msg = $"{result}";
// Passing in message msg isn't required, we can just pass in stepContext.Result
await stepContext.Context.SendActivityAsync(MessageFactory.Text(msg), cancellationToken);
Becomes:
var result = stepContext.Result;
await stepContext.Context.SendActivityAsync(MessageFactory.Text(result), cancellationToken);
So what I actually think you actually want is the following:
var dispatchResult = await cognitiveModels.DispatchService.RecognizeAsync<ReturnIntents>(dc.Context, CancellationToken.None);
Which will send the user's input off to LUIS, and deserialize the response into a ReturnIntents object.
Edit to provide solution to the OP
The ExecuteLuisQuery method called here, and defined here returns a ReturnIntents object.
This object is passed as an option to the ReturnIntentDialog here. Because this comes through as an instance of the object type you have a few options inside your FinalStepAsync method here to turn your options object into a ReturnIntents object.:
Casting
ReturnIntents returnIntents = null;
if (stepContext.Options is ReturnIntents)
{
returnIntents = (ReturnIntents)stepContext.Options;
}
Deserializing
using Newtonsoft.Json;
ReturnIntents returnIntents = null;
if (stepContext.Options is ReturnIntents)
{
returnIntents = JsonConvert.DeserializeObject<ReturnIntents>(JsonConvert.SerializeObject(stepContext.Options));
}