Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Runtime.InteropServices
 
Namespace DrawFlat
    <ToolboxBitmap(GetType(System.Windows.Forms.ComboBox))>
    Public Class FlatComboBox
        Inherits ComboBox
#Region "ComboInfoHelper"
        Friend Class ComboInfoHelper
            <DllImport("user32")>
            Private Shared Function GetComboBoxInfo(ByVal hwndCombo As IntPtr, _
              ByRef info As ComboBoxInfo) As Boolean
            End Function
#Region "RECT struct"
            <StructLayout(LayoutKind.Sequential)>
            Private Structure RECT
                Public Left As Integer
                Public Top As Integer
                Public Right As Integer
                Public Bottom As Integer
            End Structure
#End Region
#Region "ComboBoxInfo Struct"
            <StructLayout(LayoutKind.Sequential)>
            Private Structure ComboBoxInfo
                Public cbSize As Integer
                Public rcItem As RECT
                Public rcButton As RECT
                Public stateButton As IntPtr
                Public hwndCombo As IntPtr
                Public hwndEdit As IntPtr
                Public hwndList As IntPtr
            End Structure
 
#End Region
            Public Shared Function GetComboDropDownWidth() As Integer
                Dim cb As ComboBox = New ComboBox()
                Dim width As Integer = GetComboDropDownWidth(cb.Handle)
                cb.Dispose()
                Return width
            End Function
            Public Shared Function GetComboDropDownWidth(ByVal handle As _
              IntPtr) As Integer
                Dim cbi As ComboBoxInfo = New ComboBoxInfo()
                cbi.cbSize = Marshal.SizeOf(cbi)
                GetComboBoxInfo(handle, cbi)
                Dim width As Integer = cbi.rcButton.Right - cbi.rcButton.Left
                Return width
            End Function
        End Class
#End Region
        Public Const WM_ERASEBKGND As Integer = &H14
        Public Const WM_PAINT As Integer = &HF
        Public Const WM_NC_PAINT As Integer = &H85
        Public Const WM_PRINTCLIENT As Integer = &H318
        Private Shared DropDownButtonWidth As Integer = 17