Botframework v4: Uploading image to the bot in another class

Question

I have this code in OnTurnAsync() in the main bot class that let the user upload image and saved it locally and its working fine. But how can i do this if i want to do it in a different class like a MainDialog class?

Update: I manage to do it by the code below. But it is accepting everything, how can i do a validation that accepts only images?

Update: Answer below.

public class MainDialog : ComponentDialog
{
    private const string InitialId = "mainDialog";
    private const string TEXTPROMPT = "textPrompt";
    private const string ATTACHPROMPT = "attachPrompt";

    public MainDialog(string dialogId)
        : base(dialogId)
    {
        WaterfallStep[] waterfallSteps = new WaterfallStep[]
         {
             FirstStepAsync,
             SecondStepAsync,
         };
        AddDialog(new WaterfallDialog(InitialId, waterfallSteps));
        AddDialog(new AttachmentPrompt(ATTACHPROMPT));
    }

    private static async Task<DialogTurnResult> FirstStepAsync(WaterfallStepContext stepContext, CancellationToken cancellationToken = default(CancellationToken))
    {
        return await stepContext.PromptAsync(
              ATTACHPROMPT,
              new PromptOptions
              {
                  Prompt = MessageFactory.Text($"upload photo."),
                  RetryPrompt = MessageFactory.Text($"upload photo pls."),
              });
    }

    private static async Task<DialogTurnResult> SecondStepAsync(WaterfallStepContext stepContext, CancellationToken cancellationToken = default(CancellationToken))
    {
        var activity = stepContext.Context.Activity;

        if (activity.Attachments != null && activity.Attachments.Any())
        {
            foreach (var file in stepContext.Context.Activity.Attachments)
            {
                var remoteFileUrl = file.ContentUrl;

                var localFileName = Path.Combine(Path.GetTempPath(), file.Name);

                using (var webClient = new WebClient())
                {
                    webClient.DownloadFile(remoteFileUrl, localFileName);
                }

                await stepContext.Context.SendActivityAsync($"Attachment {stepContext.Context.Activity.Attachments[0].Name} has been received and saved to {localFileName}.");
            }
        }

        return await stepContext.EndDialogAsync();
    }

Managed to do it with this code.

            var activity = stepContext.Context.Activity;
        if (activity.Attachments != null && activity.Attachments.Any())
        {
            foreach (var file in stepContext.Context.Activity.Attachments)
            {
                if (file.ContentType.EndsWith("/jpg") || file.ContentType.EndsWith("/png") || file.ContentType.EndsWith("/bmp") || file.ContentType.EndsWith("/jpe"))
                {
                    var remoteFileUrl = file.ContentUrl;

                    var localFileName = Path.Combine(Path.GetTempPath(), file.Name);

                    using (var webClient = new WebClient())
                    {
                        webClient.DownloadFile(remoteFileUrl, localFileName);
                    }

                    await stepContext.Context.SendActivityAsync($"Attachment {stepContext.Context.Activity.Attachments[0].Name} has been received and saved to {localFileName}.");
                    return await stepContext.NextAsync();
                }
                else
                {
                    await stepContext.Context.SendActivityAsync($"Attachment {file.Name} is not an image, it is {file.ContentType}.");

                    // restart the dialog from top
                    return await stepContext.ReplaceDialogAsync(InitialId);
                }
            }
        }

Answer 1

Like Nicolas R said, you could do some basic validation like this:

foreach (var file in activity.Attachments)
{
    if (file.ContentType.StartsWith("image/", StringComparison.OrdinalIgnoreCase))
    {
        await turnContext.SendActivityAsync($"Attachment {file.Name} is an image of type {file.ContentType}.");
    }
    else
    {
        await turnContext.SendActivityAsync($"Attachment {file.Name} is not an image, it is {file.ContentType}.");
    }
}

This will of course allow any attachment with a content type that starts with "image/". You might not want to allow any content type that starts with "image/", in which case you'd want to make a list of accepted types like "image/png" and "image/jpeg". You might also consider checking the file extension (to see if it's ".png" or ".jpg" etc.)