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，我想改变什么）：

Printscreen

Answer 1

改变ComboBox的DropDown List的Theme边框颜色，需要处理List Control的WM_NCPAINT消息，当非客户区需要时发送给Window的句柄被绘制：通常，当显示下拉菜单时。

要获取组合框的列表控件的句柄，可以使用GetComboBoxInfo()函数：其列表控件和编辑控件的句柄以COMBOBOXINFO结构返回。

然后您可以将列表控件句柄分配给 NativeWindow，以便您可以覆盖其 WndProc 并捕获 WM_NCPAINT。
收到消息后，获取List Control的Device Context（HDC）的句柄，使用GetWindowDc()函数传递给Graphics.FromHdc()方法，创建Graphics对象可用于在此表面上绘图。

▶ 阅读有关 WM_NCPAINT 消息的文档，您可能会注意到 WPARAM 应该引用更新区域句柄：但它通常是 IntPtr.Zero，这就是我们需要 GetWindowDc() 的原因。< /p>

在（重要）之后释放设备上下文调用 ReleaseDC() 的句柄。

差不多就是这样。
自定义 ComboBox 控件公开了一个公共 ListBorderColor 属性，该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

更改 ComboBox 下拉列表边框的颜色

1 个答案: