Moving a captionless form

[Merrion]

Often, especially where a customised or skinned look is desired, the form is created with the FormBorderStyle set to FixedSingle.

However if you still want to move that skinned form you have a bit of a problem. Fortunately it is possible to handle the WM_NCHITTEST window message to make windows think the mouse is over the caption even where a form doesn't have one.

 

1. Defining a rectangle that emulates the form caption

In the form:

Public Class Form1
   Inherits System.Windows.Forms.Form

#Region "Private memeber variables"
   Dim rcCaption As Rectangle
#End Region

   Public Sub New()
       MyBase.New()

       'This call is required by the Windows Form Designer.
       InitializeComponent()

       '\\ Make the fake caption rectangle
       rcCaption = New Rectangle(0, 0, Me.Width, 29)

   End Sub

   Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint

       e.Graphics.FillRectangle(New SolidBrush(Color.Blue), rcCaption)

   End Sub

   Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
       '\\ We want to pretend that the rectangle rcCaption, is the caption bar so we can drag the form by it...
       If m.Msg = WM_NCHITTEST Then
           Call FakeCaptionForCaptionlessWindow(Me, m, rcCaption)
       Else
           MyBase.WndProc(m)
       End If
   End Sub

End Class

 

2. The WM_NCHITTEST handler

This is kept in a seperate module for reusability...

Imports System.Windows.Forms

'\\ --[ApiHitTestHandling]-------------------------------------
'\\ Used to handle the WM_HITTEST message, to allow dragging of 
'\\ captionless windows...
'\\ -----------------------------------------------------------
Module ApiHitTestHandling

   Public Const WM_NCHITTEST = &H84

   Public Enum HitTestResult
       HTBORDER = 18
       HTBOTTOM = 15
       HTBOTTOMLEFT = 16
       HTBOTTOMRIGHT = 17
       HTCAPTION = 2
       HTCLIENT = 1
       HTERROR = (-2)
       HTGROWBOX = 4
       HTHSCROLL = 6
       HTLEFT = 10
       HTMAXBUTTON = 9
       HTMENU = 5
       HTMINBUTTON = 8
       HTNOWHERE = 0
       HTRIGHT = 11
       HTSYSMENU = 3
       HTTOP = 12
       HTTOPLEFT = 13
       HTTOPRIGHT = 14
       HTVSCROLL = 7
       HTTRANSPARENT = (-1)
       HTOBJECT = 19
       HTCLOSE = 20
       HTHELP = 21
   End Enum

   Public Sub FakeCaptionForCaptionlessWindow(ByVal fParent As Form, ByRef m As Message, ByVal CaptionRectangle As Rectangle)

       If m.Msg = WM_NCHITTEST Then
           '\\ If the mouse is in the rectangle that is considered to be the caption set the return value to HTCAPTION
           Dim ptClickLocation As New Point(m.LParam.ToInt32)
           ptClickLocation = fParent.PointToClient(ptClickLocation)

           If CaptionRectangle.Contains(ptClickLocation) Then
               m.Result = New IntPtr(HitTestResult.HTCAPTION)
           Else
               m.Result = New IntPtr(HitTestResult.HTCLIENT)
           End If
       End If
   End Sub

End Module