如何在TextBox中禁用鼠标移动所选文本？

using System;
using System.Windows.Forms;

public class CustomTextBox : TextBox
{
    protected override void OnMouseDown(MouseEventArgs e)
    {
        // 禁用默认的鼠标按下行为
        this.SelectionLength = 0;
        base.OnMouseDown(e);
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        // 禁用默认的鼠标移动行为
        this.SelectionLength = 0;
        base.OnMouseMove(e);
    }
}

public partial class MainForm : Form
{
    public MainForm()
    {
        InitializeComponent();

        CustomTextBox customTextBox = new CustomTextBox();
        customTextBox.Location = new System.Drawing.Point(10, 10);
        customTextBox.Size = new System.Drawing.Size(200, 20);
        this.Controls.Add(customTextBox);
    }
}