UXTheme'd GroupBox control

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Introduction

If you have ever used Application.EnableVisualSyles and a TabControl you must have noticed that Microsoft has left out theme support for the TabPages. It is well known to get around this problem while using a UXTheme wrapper to draw the theme background onto the TabPage. However, one day I went to place a GroupBox control onto a UXThemed TabControl and then I noticed that the GroupBox did not fully take up the application's visual theme either, and it wasn't as easy to fix as with the TabPage.

While searching the internet I found some C# code on a .NET newsgroup and converted it to VB, however there were a few overflows which occurred and when adding controls onto the GroupBox they had a solid black background, took parts of the background from other parts of the screen or created a giant hole in the application and you were able to see the desktop.

A big Thank You goes to Ying-Shen Yu for posting the original code in C#.

Using the code

The control first overrides the BackColor property to allow a transparent background to be set for the GroupBox. This is required for the Label on the top of the GroupBox. Secondly, we catch the Windows message for WM_PAINTBKGRD and replace it with our custom drawing code. Finally, we override the OnPaint methods so that the child controls draw properly inside the GroupBox.

Namespace Controls

    Public Class GroupBox

        Inherits System.Windows.Forms.GroupBox

        Public Overrides Property BackColor() As Color
            Get
                Return MyBase.BackColor
            End Get
            Set(ByVal Value As Color)

               MyBase.SetStyle(ControlStyles.SupportsTransparentBackColor, True)
               MyBase.SetStyle(ControlStyles.UserPaint, True)
               MyBase.BackColor = Value

            End Set
        End Property

        Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

            If (m.Msg = 20) And (Me.FlatStyle = FlatStyle.System) Then
               MyBase.SetStyle(ControlStyles.SupportsTransparentBackColor, True)
               MyBase.SetStyle(ControlStyles.UserPaint, True)
               Dim g As Graphics = Graphics.FromHdcInternal(m.WParam)
               OnPaintBackground(New PaintEventArgs(g, New Rectangle(0, 0, _
                                                               Width, Height)))
               g.Dispose()
               MyBase.SetStyle(ControlStyles.SupportsTransparentBackColor, False)
               MyBase.SetStyle(ControlStyles.UserPaint, False)
               Exit Sub
            End If

            MyBase.WndProc(m)

        End Sub

        Protected Overrides Sub OnPaintBackground(ByVal pevent _
                           As System.Windows.Forms.PaintEventArgs)
            System.Windows.Forms.Themes.UxTheme.DrawThemeParentBackground(Me, _
                                          pevent.Graphics, pevent.ClipRectangle)
        End Sub

        Protected Overrides Sub OnPaint(ByVal e As _
                            System.Windows.Forms.PaintEventArgs)
          System.Windows.Forms.Themes.UxTheme.DrawThemeParentBackground(Me, _
             e.Graphics, New Rectangle(0, 0, e.ClipRectangle.Width, _
             e.ClipRectangle.Height))
        End Sub

    End Class

End Namespace

Using the control is no different from using a normal GroupBox control (in fact, this control inherits the GroupBox control and overrides some of the functions).

Dim oGroupBox as New Controls.GroupBox
oGroupBox.Text = "Test Group"

Dim oLabel As New System.Windows.Forms.Label
oLabel.Text = "Test Label"
oLabel.BackColor = Color.Transparent
oLabel.Location = New Point(5, 5)
oLabel.AutoSize = True

oGroupBox.Controls.Add(oLabel)

Points of interest

I had a rather strange experience getting the child controls to draw the backgrounds properly, I had random results ranging from an almost transparent application, to half the controls drawing properly. This was fixed by overriding the OnPaint method of the GroupBox and replacing it with the UXTheme drawing routine.

If you look up Graphics.FromHdcInternal on MSDN, it says "Do Not Use!" Oops :)

History

• 14^th December 2004 - Initial version.

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