chapplication/Chapplication/MainWindow.axaml.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.Input;
using Avalonia.Interactivity;
using Chapplication.Models;

namespace Chapplication;

public partial class MainWindow : Window
{
    
    private ObservableCollection<string> _messages = new();
    
    public MainWindow()
    {
        InitializeComponent();

        ChatBox.ItemsSource = _messages;
    }

    private void SubmitButton_OnClick(object? sender, RoutedEventArgs e)
    {
        SendMessage();
    }

    private void ChatInputBox_OnKeyDown(object? sender, KeyEventArgs e)
    {
        if (e.Key == Key.Enter)
        {
            SendMessage();
        }
    }
    
    private void SendMessage()
    {
        if (string.IsNullOrWhiteSpace(ChatInputBox.Text))
        {
            return;
        }
        
        _messages.Add(ChatInputBox.Text);
        ChatInputBox.Text = string.Empty;
        ChatInputBox.Focus();
    }
}