Make a borderless form movable?

Question

This article on CodeProject details a technique. Is basically boils down to:

public const int WM_NCLBUTTONDOWN = 0xA1;
public const int HT_CAPTION = 0x2;

[System.Runtime.InteropServices.DllImport("user32.dll")]
public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);
[System.Runtime.InteropServices.DllImport("user32.dll")]
public static extern bool ReleaseCapture();

private void Form1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{     
    if (e.Button == MouseButtons.Left)
    {
        ReleaseCapture();
        SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
    }
}

This essentially does exactly the same as grabbing the title bar of a window, from the window manager's point of view.

Let's not make things any more difficult than they need to be. I've come across so many snippets of code that allow you to drag a form around (or another Control). And many of them have their own drawbacks/side effects. Especially those ones where they trick Windows into thinking that a Control on a form is the actual form.

That being said, here is my snippet. I use it all the time. I'd also like to note that you should not use this.Invalidate(); as others like to do because it causes the form to flicker in some cases. And in some cases so does this.Refresh. Using this.Update, I have not had any flickering issues:

private bool mouseDown;
private Point lastLocation;

    private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        mouseDown = true;
        lastLocation = e.Location;
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        if(mouseDown)
        {
            this.Location = new Point(
                (this.Location.X - lastLocation.X) + e.X, (this.Location.Y - lastLocation.Y) + e.Y);

            this.Update();
        }
    }

    private void Form1_MouseUp(object sender, MouseEventArgs e)
    {
        mouseDown = false;
    }

Another simpler way to do the same thing.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        // set this.FormBorderStyle to None here if needed
        // if set to none, make sure you have a way to close the form!
    }
    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == WM_NCHITTEST)
            m.Result = (IntPtr)(HT_CAPTION);
    }

    private const int WM_NCHITTEST = 0x84;
    private const int HT_CLIENT = 0x1;
    private const int HT_CAPTION = 0x2;
}

use MouseDown, MouseMove and MouseUp. You can set a variable flag for that. I have a sample, but I think you need to revise.

I am coding the mouse action to a panel. Once you click the panel, your form will move with it.

//Global variables;
private bool _dragging = false;
private Point _offset;
private Point _start_point=new Point(0,0);


private void panel1_MouseDown(object sender, MouseEventArgs e)
{
   _dragging = true;  // _dragging is your variable flag
   _start_point = new Point(e.X, e.Y);
}

private void panel1_MouseUp(object sender, MouseEventArgs e)
{
   _dragging = false; 
}

private void panel1_MouseMove(object sender, MouseEventArgs e)
{
  if(_dragging)
  {
     Point p = PointToScreen(e.Location);
     Location = new Point(p.X - this._start_point.X,p.Y - this._start_point.Y);     
  }
}