How to detect a left mouse click on a Winform titlebar

This simple code will trap a left mouse click on a winform titlebar and sets the opacity of the form to 50%, when the left mouse button is released the forms opaccity is set back to 100%

       Private Const WM_NCLBUTTONDOWN As Long = &HA1
       Private Const WM_NCLBUTTONUP As Long = &HA0

Protected Overrides Sub DefWndProc(ByRef m As System.Windows.Forms.Message)
  ' -- You might want to trap for user clicking, min, max or close and ignore
  ' -- Trap left mouse click down on titlebar
  If CLng(m.Msg) = WM_NCLBUTTONDOWN Then
    ' -- Set the forms opacity
    If Me.Opacity <> 0.5 Then Me.Opacity = 0.5
    ' -- Trap left mouse click up on titlebar
  ElseIf CLng(m.Msg) = WM_NCLBUTTONUP Then
    If Me.Opacity <> 1.0 Then Me.Opacity = 1.0
  End If

   ' -- Business as usual
   MyBase.DefWndProc(m)
End Sub

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TheAphextwin

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How to detect a left mouse click on a Winform titlebar [modified]

Morteza Karimian

3:31 19 Feb '11

How to detect a left mouse click on a Winform titlebar:
1.create two private,const and long variable then initialize.like this:

private const long WM_NCLBUTTONDOWN = 0xA1;//161
   private const long WM_NCLBUTTONUP = 0xA0;//160

2.override the WndProc method to detect "left mouse click on a Winform titlebar " message and do any work,like this:

protected override void WndProc(ref Message m)
        {
            if (m.Msg == WM_NCLBUTTONDOWN)
            {
                if (this.Opacity != 0.5)
                {
                    this.Opacity = 0.5;
                }
            }
            if (m.Msg == WM_NCLBUTTONUP)
            {
                if (this.Opacity != 1.0)
                {
                    this.Opacity = 1.0;
                }
            }
            base.WndProc(ref m);          
        }

3." if (m.Msg == WM_NCLBUTTONDOWN){}" this block detemine that click is down on the title bar of the form.
4."if (m.Msg == WM_NCLBUTTONUP){}" this block detemine that click is up on the title bar of the form.
5.finish

full C# code is like below:

using System.Windows.Forms;
 
namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private const long WM_NCLBUTTONDOWN = 0xA1;//161
        private const long WM_NCLBUTTONUP = 0xA0;//160

        protected override void WndProc(ref Message m)
        {
            if (m.Msg == WM_NCLBUTTONDOWN)
            {
                if (this.Opacity != 0.5)
                {
                    this.Opacity = 0.5;
                }
            }
            if (m.Msg == WM_NCLBUTTONUP)
            {
                if (this.Opacity != 1.0)
                {
                    this.Opacity = 1.0;
                }
            }
            base.WndProc(ref m);          
        }
    }
}