Marshal.PtrToSt ructure crashes

[Tyron]

I want to get the Position of the Mouse when the User click in the
non-client area of a Window.
WM_NCLBUTTONDOW N seems to be the right Message for this - and the LParam
contains a POINTS struct of the Mouse Position (so the speak on MSDN.
[http://msdn.microsoft.com/library/de...uttondown.asp])
But when I try to convert the IntPtr to a Struct, it throws a
Argument.NullRe ferenceExceptio n
Code:
[StructLayout(La youtKind.Sequen tial, CharSet=CharSet .Ansi)]
public struct POINT {
public Int16 x;
public Int16 y;
}

protected override void WndProc(ref Message m)
{
if(m.Msg==WM_NC LBUTTONDOWN) {
POINT pnt = new POINT();
// crashes
pnt = (POINT)Marshal. PtrToStructure( m.LParam,typeof (POINT));
// label2.Text = pnt.x + "/" + pnt.y;
}
base.WndProc(re f m);
}

[Dave]

I belive the X and Y coords of the unmanged Point structure are 32 bit integers.

You can use System.Windows. Forms.Control.M ousePosition as an easier solution.
--
Dave Sexton
dave@www..jwaon line..com
-----------------------------------------------------------------------
<Tyron> wrote in message news:Os******** ******@TK2MSFTN GP15.phx.gbl...

I want to get the Position of the Mouse when the User click in the
non-client area of a Window.
WM_NCLBUTTONDOW N seems to be the right Message for this - and the LParam
contains a POINTS struct of the Mouse Position (so the speak on MSDN.
[http://msdn.microsoft.com/library/de...uttondown.asp])
But when I try to convert the IntPtr to a Struct, it throws a
Argument.NullRe ferenceExceptio n
Code:
[StructLayout(La youtKind.Sequen tial, CharSet=CharSet .Ansi)]
public struct POINT {
public Int16 x;
public Int16 y;
}

protected override void WndProc(ref Message m)
{
if(m.Msg==WM_NC LBUTTONDOWN) {
POINT pnt = new POINT();
// crashes
pnt = (POINT)Marshal. PtrToStructure( m.LParam,typeof (POINT));
// label2.Text = pnt.x + "/" + pnt.y;
}
base.WndProc(re f m);
}

[John Sun]

Tyron wrote:

I want to get the Position of the Mouse when the User click in the
non-client area of a Window.
WM_NCLBUTTONDOW N seems to be the right Message for this - and the LParam
contains a POINTS struct of the Mouse Position (so the speak on MSDN.
[http://msdn.microsoft.com/library/de...uttondown.asp])
But when I try to convert the IntPtr to a Struct, it throws a
Argument.NullRe ferenceExceptio n
Code:
[StructLayout(La youtKind.Sequen tial, CharSet=CharSet .Ansi)]
public struct POINT {
public Int16 x;
public Int16 y;
}

protected override void WndProc(ref Message m)
{
if(m.Msg==WM_NC LBUTTONDOWN) {
POINT pnt = new POINT();
// crashes
pnt = (POINT)Marshal. PtrToStructure( m.LParam,typeof (POINT));
// label2.Text = pnt.x + "/" + pnt.y;
}
base.WndProc(re f m);
}

System.Drawing. Point actually takes m.LParam in one of its
constructor, I think this may be a easier way for you to get the positon.

HTH.

Jianwei

[Tyron]

Yay, a simple Point pnt = new Point((int)m.LP aram) works wonderful.

Thanks Guys!