VisualComponents/VisualComponentsLib/UserTextBox.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace VisualComponentsLib
{
    public partial class UserTextBox : UserControl
    {
        public string inputString
        {
            get => textBox.Text;
            set => textBox.Text = value;
        }

        public new event EventHandler? TextChanged
        {
            add => textBox.Text = value.ToString();
            remove => textBox.Text = string.Empty;
        }

        public UserTextBox()
        {
            InitializeComponent();
        }

        public void clickCheckBox()
        {
            if(checkBox.Checked)
            {
                textBox.ReadOnly = true;

                inputString = string.Empty;

                textBox.Text = string.Empty;
            }
            
            if(!checkBox.Checked)
            {
                try
                {
                    double support;

                    if (Double.TryParse(textBox.Text, out support))
                    {
                        inputString = textBox.Text;
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Введённое значение не является вещественным числом.");
                }
            }
        }
    }
}