pepoluan pepoluan - 2 months ago 13
Vb.net Question

How to make a custom ComboBox (OwnerDrawFixed) looks 3D like the standard ComboBox?

I am making a custom ComboBox, inherited from Winforms' standard ComboBox. For my custom ComboBox, I set

DrawMode
to
OwnerDrawFixed
and
DropDownStyle
to
DropDownList
. Then I write my own
OnDrawItem
method. But I ended up like this:

Standard vs Custom ComboBoxes

How do I make my Custom ComboBox to look like the Standard one?




Update 1: ButtonRenderer



After searching all around, I found the
ButtonRenderer
class
. It provides a
DrawButton
static/shared method which -- as the name implies -- draws the proper 3D button. I'm experimenting with it now.




Update 2: What overwrites my control?



I tried using the Graphics properties of various objects I can think of, but I always fail. Finally, I tried the Graphics of the form, and apparently something is overwriting my button.

Here's the code:

Protected Overrides Sub OnDrawItem(ByVal e As System.Windows.Forms.DrawItemEventArgs)
Dim TextToDraw As String = _DefaultText
__Brush_Window.Color = Color.FromKnownColor(KnownColor.Window)
__Brush_Disabled.Color = Color.FromKnownColor(KnownColor.GrayText)
__Brush_Enabled.Color = Color.FromKnownColor(KnownColor.WindowText)
If e.Index >= 0 Then
TextToDraw = _DataSource.ItemText(e.Index)
End If
If TextToDraw.StartsWith("---") Then TextToDraw = StrDup(3, ChrW(&H2500)) ' U+2500 is "Box Drawing Light Horizontal"
If (e.State And DrawItemState.ComboBoxEdit) > 0 Then
'ButtonRenderer.DrawButton(e.Graphics, e.Bounds, VisualStyles.PushButtonState.Default)
Else
e.DrawBackground()
End If
With e
If _IsEnabled(.Index) Then
.Graphics.DrawString(TextToDraw, Me.Font, __Brush_Enabled, .Bounds.X, .Bounds.Y)
Else
'.Graphics.FillRectangle(__Brush_Window, .Bounds)
.Graphics.DrawString(TextToDraw, Me.Font, __Brush_Disabled, .Bounds.X, .Bounds.Y)
End If
End With
TextToDraw = Nothing
ButtonRenderer.DrawButton(Me.Parent.CreateGraphics, Me.ClientRectangle, VisualStyles.PushButtonState.Default)

'MyBase.OnDrawItem(e)
End Sub


And here's the result:

Overwritten ButtonRenderer

Replacing
Me.Parent.CreateGraphics
with
e.Graphics
got me this:

Clipped ButtonRenderer

And doing the above + replacing
Me.ClientRectangle
with
e.Bounds
got me this:

Shrunk ButtonRenderer

Can anyone point me whose Graphics I must use for the
ButtonRenderer.DrawButton
method?

PS: The bluish border is due to my using PushButtonState.Default instead of PushButtonState.Normal




I Found An Answer! (see below)


Answer

I forgot where I found the answer... I'll edit this answer when I remember.

But apparently, I need to set the Systems.Windows.Forms.ControlStyles flags. Especially the ControlStyles.UserPaint flag.

So, my New() now looks like this:

Private _ButtonArea as New Rectangle

Public Sub New()
  ' This call is required by the designer.
  InitializeComponent()
  ' Add any initialization after the InitializeComponent() call.
  MyBase.SetStyle(ControlStyles.Opaque Or ControlStyles.UserPaint, True)
  MyBase.DrawMode = Windows.Forms.DrawMode.OwnerDrawFixed
  MyBase.DropDownStyle = ComboBoxStyle.DropDownList
  ' Cache the button's modified ClientRectangle (see Note)
  With _ButtonArea
    .X = Me.ClientRectangle.X - 1
    .Y = Me.ClientRectangle.Y - 1
    .Width = Me.ClientRectangle.Width + 2
    .Height = Me.ClientRectangle.Height + 2
  End With
End Sub

And now I can hook into the OnPaint event:

Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
  If Me.DroppedDown Then
    ButtonRenderer.DrawButton(Me.CreateGraphics, _ButtonArea, VisualStyles.PushButtonState.Pressed)
  Else
    ButtonRenderer.DrawButton(Me.CreateGraphics, _ButtonArea, VisualStyles.PushButtonState.Normal)
  End If
  MyBase.OnPaint(e)
End Sub

Note: Yes, the _ButtonArea rectangle must be enlarged by 1 pixel to all directions (up, down, left, right), or else there will be a 1-pixel 'perimeter' around the ButtonRenderer that shows garbage. Made me crazy for awhile until I read that I must enlarge the Control's rect for ButtonRenderer.