如何更改ComboBox下拉列表边框的颜色

Question

我的代码：

Private Sub ComboBox2_DrawItem(sender As Object, e As DrawItemEventArgs) Handles ComboBox2.DrawItem
    If e.Index < 0 Then
        Return
    End If
    e.Graphics.TextRenderingHint = Drawing.Text.TextRenderingHint.AntiAlias
    Dim CB As ComboBox = TryCast(sender, ComboBox)
    If (e.State And DrawItemState.Selected) = DrawItemState.Selected Then
        e.Graphics.FillRectangle(New SolidBrush(Color.DarkRed), e.Bounds)
    Else
        e.Graphics.FillRectangle(New SolidBrush(CB.BackColor), e.Bounds)
    End If
    e.Graphics.DrawString(CB.Items(e.Index).ToString(), e.Font, New SolidBrush(CB.ForeColor), New Point(e.Bounds.X, e.Bounds.Y))
End Sub

结果（注意蓝色边缘，这是我想要更改的）：

- Sérgio Jesus

Answer 1

要更改ComboBox的DropDown List主题边框颜色，您需要处理List Control的WM_NCPAINT消息，该消息在需要绘制非客户区域时发送到窗口的句柄：通常在显示DropDown时。

要获取ComboBox的List Control的句柄，您可以使用GetComboBoxInfo()函数：其List Control和Edit Control的句柄以COMBOBOXINFO结构返回。

您可以将列表控件句柄分配给NativeWindow，以便覆盖其WndProc并捕获 WM_NCPAINT 。当收到消息时，使用GetWindowDc（）函数获取列表控件的设备上下文（HDC）句柄，并将其传递给Graphics.FromHdc（）方法，创建可用于在此表面上绘制的Graphics对象。

▶ 阅读有关 WM_NCPAINT 消息的文档，您可能会注意到 WPARAM 应引用更新区域句柄：但通常为IntPtr.Zero，这就是为什么我们需要 GetWindowDc（）的原因。

释放设备上下文的句柄后，调用 ReleaseDC()（重要）。

就是这样。 自定义组合框控件公开了一个名为 ListBorderColor 的公共属性，用于在设计时和运行时设置列表控件边框的颜色。

Imports System.ComponentModel
Imports System.Drawing
Imports System.Runtime.InteropServices
Imports System.Windows.Forms

<DesignerCategory("code")>
Public Class ComboBoxExt
    Inherits ComboBox

    Private listControl As ListNativeWindow = Nothing
    Private m_ListBorderColor As Color = Color.Transparent

    Public Sub New()
    End Sub

    <DefaultValue(GetType(Color), "Transparent")>
    Public Property ListBorderColor As Color
        Get
            Return m_ListBorderColor
        End Get
        Set
            m_ListBorderColor = Value
            If listControl IsNot Nothing Then
                listControl.BorderColor = m_ListBorderColor
            End If
        End Set
    End Property

    Protected Overrides Sub OnHandleCreated(e As EventArgs)
        MyBase.OnHandleCreated(e)
        listControl = New ListNativeWindow(GetComboBoxListInternal(Me.Handle))
        listControl.BorderColor = ListBorderColor
    End Sub

    Protected Overrides Sub OnHandleDestroyed(e As EventArgs)
        listControl.ReleaseHandle()
        MyBase.OnHandleDestroyed(e)
    End Sub

    Public Class ListNativeWindow
        Inherits NativeWindow

        Public Sub New()
            Me.New(IntPtr.Zero)
        End Sub

        Public Sub New(hWnd As IntPtr)
            If hWnd <> IntPtr.Zero Then AssignHandle(hWnd)
        End Sub

        Public Property BorderColor As Color = Color.Transparent

        Protected Overrides Sub WndProc(ByRef m As Message)
            MyBase.WndProc(m)
            Select Case m.Msg
                Case WM_NCPAINT
                    Dim hDC As IntPtr = GetWindowDC(Me.Handle)
                    Try
                        Using g = Graphics.FromHdc(hDC),
                            pen = New Pen(BorderColor)
                            Dim rect = g.VisibleClipBounds
                            g.DrawRectangle(pen, 0, 0, rect.Width - 1, rect.Height - 1)
                        End Using
                    Finally
                        ReleaseDC(Me.Handle, hDC)
                    End Try
                m.Result = IntPtr.Zero
            End Select
        End Sub
    End Class


    <DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Friend Shared Function GetComboBoxInfo(hWnd As IntPtr, ByRef pcbi As COMBOBOXINFO) As Boolean
    End Function

    <DllImport("user32.dll", SetLastError:=True)>
    Friend Shared Function GetWindowDC(hWnd As IntPtr) As IntPtr
    End Function

    <DllImport("user32.dll", SetLastError:=True)>
    Friend Shared Function ReleaseDC(hWnd As IntPtr, hDc As IntPtr) As Boolean
    End Function

    Friend Const WM_NCPAINT As Integer = &H85

    <StructLayout(LayoutKind.Sequential)>
    Friend Structure COMBOBOXINFO
        Public cbSize As Integer
        Public rcItem As Rectangle
        Public rcButton As Rectangle
        Public buttonState As Integer
        Public hwndCombo As IntPtr
        Public hwndEdit As IntPtr
        Public hwndList As IntPtr
        Public Sub Init()
            cbSize = Marshal.SizeOf(Of COMBOBOXINFO)()
        End Sub
    End Structure

    Friend Function GetComboBoxListInternal(cboHandle As IntPtr) As IntPtr
        Dim cbInfo = New COMBOBOXINFO()
        cbInfo.Init()
        GetComboBoxInfo(cboHandle, cbInfo)
        Return cbInfo.hwndList
    End Function
End Class

- Jimi