C#

public partial class MyForm : Form
{
    const Int32 HTCAPTION = 0x2;
    const Int32 WM_NCLBUTTONDBLCLK = 0xA3;
 
    protected override void WndProc(ref Message msg)
    {
        switch (msg.Msg)
        {
           case WM_NCLBUTTONDBLCLK:
               if (msg.WParam.ToInt32() == HTCAPTION)
                   return;
               break;
        };
        base.WndProc(ref msg);
    }
}

jrahma wrote:

form ID like FRM123

static int? Convert (string value)
 {
     if (string.IsNullOrEmpty(value))
         return null;

     int returnedInt;
     if (int.TryParse(value, out returnedInt))
         return returnedInt;

     // I've asssumed that you want null if the value is unparsable
     // You might want to throw an argument exception instead here.
     return null;
 }

public int? ToNullableInt32(string s)
{
    int i;
    return (Int32.TryParse(s, out i)) ? i : null;
}

//........

String s ="";
int? nullint = ToNullableInt32(s);