为什么我按 D 时矩形不动？

问：

所以我正在尝试为大学的一个项目制作一个类似油漆的程序，我必须让形状移动。我们的教授建议我们使用 KeyDown，但由于某种原因，我无法弄清楚为什么它不会移动。代码如下

public partial class Form1 : Form
{
    Rectangle rect = new Rectangle();
    bool isMouseDown = false;
    public Form1()
    {
        InitializeComponent();

        this.Width = 900;
        this.Height = 700;
        bm = new Bitmap(pic.Width, pic.Height);
        bm2 = new Bitmap(pic2.Width, pic2.Height);
        g = Graphics.FromImage(bm);
        g2 = Graphics.FromImage(bm2);
        g.Clear(Color.Transparent);
        pic.Image = bm;
        pic2.Image = bm2;
        pic.Parent = pic2;
        pic.BackColor = Color.Transparent;
        pic2.BackColor = Color.Transparent;
    }

    Bitmap bm, bm2;
    Graphics g, g2;
    bool paint = false;
    Point px, py;
    private Point MouseDownLocation;
    Pen p = new Pen(Color.Black, 1);
    int index;
    Pen erase = new Pen(Color.Transparent, 10);
    int x, y, sX, sY, cX, cY;

    ColorDialog cd = new ColorDialog();
    Color new_color;

 private void pic_MouseDown(object sender, MouseEventArgs e)
 {
     paint = true;
     MouseDownLocation = e.Location;
     py = e.Location;
     px = e.Location;

     cX = e.X;
     cY = e.Y;

     sX = e.X;
     sY = e.Y;
 }

private void pic_MouseMove(object sender, MouseEventArgs e)
{
    if (paint)
    {
        if (index == 1)
        {
            px = e.Location;
            g.DrawLine(p, px, py);
            py = px;
        }
        if (index == 2)
        {
            px = e.Location;
            g.DrawLine(erase, px, py);
            py = px;
        }
    }
    pic.Refresh();

    x = e.X;
    y = e.Y;
    sX = e.X - cX;
    sY = e.Y - cY;
}

private void pic_MouseUp(object sender, MouseEventArgs e)
{
    isMouseDown = false;
    paint = false;

    sX = x - cX;
    sY = y - cY;

    if (index == 3)
    {
        g.DrawEllipse(p, cX, cY, sX, sY);
    }
    if (index == 4)
    {
        rect = new Rectangle(cX, cY, sX, sY);
        g.DrawRectangle(p, rect);
    }
    if (index == 5)
    {
        g.DrawLine(p, cX, cY, x, y);
    }

}

private void pic_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;

    if (paint)
    {
        if (index == 3)
        {
            g.DrawEllipse(p, cX, cY, sX, sY);
        }
        if (index == 4)
        {
            g.DrawRectangle(p, rect);
        }
        if (index == 5)
        {
            g.DrawLine(p, cX, cY, x, y);
        }
    }
}

private void Form1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyData == Keys.D)
    {
        rect.X += 10;
        
    }
}

我尝试使用Form1_KeyDown功能移动它，但我无法弄清楚或找到任何有帮助的在线资源。