Discord.Net/docs/guides/int_basics/modals/intro.md

• Modals
• • Getting started with modals
  • • What is a modal?
    • Using modals
    • Respond to modals

Modals

Getting started with modals

This guide will show you how to use modals and give a few examples of
valid use cases. If your question is not covered by this guide ask in the
Discord.Net Discord Server.

What is a modal?

Modals are forms bots can send when responding to interactions. Modals
are sent to Discord as an array of message components and converted
into the form layout by user's clients. Modals are required to have a
custom id, title, and at least one component.

When users submit modals, your client fires the ModalSubmitted event.
You can get the components of the modal from the Data.Components property
on the SocketModal:

Using modals

Lets create a simple modal with an entry field for users to
tell us their favorite food. We can start by creating a slash
command that will respond with the modal.

[SlashCommand("food", "Tell us about your favorite food!")]
public async Task FoodPreference()
{
    // send a modal
}

Now that we have our command set up, we need to build a modal.
We can use the aptly named ModalBuilder for that:

Method	Description
WithTitle	Sets the modal's title.
WithCustomId	Sets the modal's custom id.
AddTextInput	Adds a TextInputBuilder to the modal.
AddComponents	Adds multiple components to the modal.
Build	Builds the ModalBuilder into a Modal.

We know we need to add a text input to the modal, so let's look at that
method's parameters.

Parameter	Description
label	Sets the input's label.
customId	Sets the input's custom id.
style	Sets the input's style.
placeholder	Sets the input's placeholder.
minLength	Sets the minimum input length.
maxLength	Sets the maximum input length.
required	Sets whether or not the modal is required.
value	Sets the input's default value.

To make a basic text input we would only need to set the label and
customId, but in this example we will also use the placeholder
parameter. Next we can build our modal:

var mb = new ModalBuilder()
    .WithTitle("Fav Food")
    .WithCustomId("food_menu")
    .AddTextInput("What??", "food_name", placeholder:"Pizza")
    .AddTextInput("Why??", "food_reason", TextInputStyle.Paragraph, 
        "Kus it's so tasty");

Now that we have a ModalBuilder we can update our command to respond
with the modal.

[SlashCommand("food", "Tell us about your favorite food!")]
public async Task FoodPreference()
{
    var mb = new ModalBuilder()
    .WithTitle("Fav Food")
    .WithCustomId("food_menu")
    .AddTextInput("What??", "food_name", placeholder:"Pizza")
    .AddTextInput("Why??", "food_reason", TextInputStyle.Paragraph, 
        "Kus it's so tasty");
    
    await Context.Interaction.RespondWithModalAsync(mb.Build());
}

When we run the command, our modal should pop up:

Respond to modals

[!WARNING]
Modals can not be sent when respoding to a modal.

Once a user has submitted the modal, we need to let everyone know what
their favorite food is. We can start by hooking a task to the client's
ModalSubmitted event.

_client.ModalSubmitted += async modal =>
{
    // Get the values of components.
    List<SocketMessageComponentData> components =
        modal.Data.Components.ToList();
    string food = components
        .Where(x => x.CustomId == "food_name").First().Value;
    string reason = components
        .Where(x => x.CustomId == "food_reason").First().Value;

    // Build the message to send.
    string message = "hey @everyone; I just learned " + 
        $"{modal.User.Mention}'s favorite food is " +
        $"{food} because {reason}.";

    // Specify the AllowedMentions so we don't actually ping everyone.
    AllowedMentions mentions = new AllowedMentions();
    mentions.AllowedTypes = AllowedMentionTypes.Users;

    // Respond to the modal.
    await modal.RespondAsync(message, allowedMentions:mentions);
}

Now responding to the modal should inform everyone of our tasty
choices.