Drag and drop rectangle in C#

Question

I want to know how to draw rectangle in C# and make it dragged and dropped in the page here my code to draw it but I cannot drag or drop it.

public partial class Form1 : Form
{
    public bool drag = false;
    int cur_x, cur_y;
    Rectangle rec = new Rectangle(10, 10, 100, 100);
    public Form1()
    {
        InitializeComponent();
    }

    protected override void OnPaint(PaintEventArgs r)
    {
        base.OnPaint(r);
        Graphics g = r.Graphics;
        //g.DrawRectangle(Pens.Black, rec);
        g.FillRectangle(Brushes.Aquamarine, rec);

    }
    private void recmousedown(object sender, MouseEventArgs m)
    {
        if (m.Button != MouseButtons.Left)
            return;
        rec = new Rectangle(m.X, m.Y,100,100);

        drag = true;
        cur_x = m.X;
        cur_y = m.Y;
    }

    private void recmousemove(object sender, MouseEventArgs m)
    {
        if (m.Button != MouseButtons.Left)
            return;

       rec.X = m.X;
       rec.Y = m.Y;
       Invalidate();
    }
}

Answer 1

You're pretty close, you just need to initialize the rectangle better and adjust the rectangle size in the Move event:

  public partial class Form1 : Form {
    public Form1() {
      InitializeComponent();
      this.DoubleBuffered = true;
    }
    Rectangle rec = new Rectangle(0, 0, 0, 0);

    protected override void OnPaint(PaintEventArgs e) {
      e.Graphics.FillRectangle(Brushes.Aquamarine, rec);
    }
    protected override void OnMouseDown(MouseEventArgs e) {
      if (e.Button == MouseButtons.Left) {
        rec = new Rectangle(e.X, e.Y, 0, 0);
        Invalidate();
      }
    }
    protected override void OnMouseMove(MouseEventArgs e) {
      if (e.Button == MouseButtons.Left) {
        rec.Width = e.X - rec.X;
        rec.Height = e.Y - rec.Y;
        Invalidate();
      }
    }
  }

Answer 2

You could try the approach in this article: http://beta.codeproject.com/KB/GDI-plus/flickerFreeDrawing.aspx