VB圆形进度条BackColor透明属性失效问题求助

问题说明 #

找到的Visual Basic圆形进度条控件中，XCoder提供的代码虽支持设置BackColor为Transparent，但实际设置后背景并未透明，无错误提示或日志，VS2022及旧版本均存在此问题，需修改代码实现真正的背景透明。

具体修改步骤 #

• 调整控件样式：移除ControlStyles.Opaque样式，启用完整的透明支持样式，确保控件能正确处理透明背景
• 条件绘制背景椭圆：仅当BackColor不透明时，才绘制中间的椭圆背景，避免覆盖父控件内容
• 重写背景绘制逻辑：修改OnPaintBackground方法，不调用基类实现，防止默认绘制不透明背景
• 修正透明背景绘制对象：在PaintTransparentBackground方法中使用绘制位图的Graphics对象，正确绘制父控件背景

修改后的完整代码 #

Imports System.ComponentModel
Imports System.Drawing.Drawing2D
Public Class CircularProgressBar
    Inherits UserControl
    Public Enum _ProgressShape
        Round
        Flat
    End Enum
    Public Enum _TextMode
        None
        Value
        Percentage
        [Custom]
    End Enum
    Private _Value As Integer = 0
    Private _Maximum As Integer = 100
    Private _LineWitdh As Integer = 5
    Private _BarWidth As Single = 11
    Private _ProgressColor1 As Color = Color.Orange
    Private _ProgressColor2 As Color = Color.Orange
    Private _LineColor As Color = Color.LightGray
    Private _GradientMode As LinearGradientMode = LinearGradientMode.ForwardDiagonal
    Private ProgressShapeVal As _ProgressShape
    Private ProgressTextMode As _TextMode
    Private _ShadowOffset As Single = 0
    Public Sub New()
        MyBase.SuspendLayout()
        ' 启用正确的透明支持样式
        SetStyle(ControlStyles.AllPaintingInWmPaint Or ControlStyles.UserPaint Or 
                 ControlStyles.ResizeRedraw Or ControlStyles.OptimizedDoubleBuffer Or 
                 ControlStyles.SupportsTransparentBackColor, True)
        BackColor = SystemColors.Control
        ForeColor = Color.DimGray
        Size = New Size(75, 75)
        Font = New Font("Segoe UI", 15)
        MinimumSize = New Size(58, 58)
        DoubleBuffered = True
        LineColor = Color.LightGray
        Value = 50
        ProgressShape = _ProgressShape.Flat
        TextMode = _TextMode.Percentage
        MyBase.ResumeLayout(False)
        MyBase.PerformLayout()
    End Sub
    <Description("Integer Value that determines the position of the Progress Bar."), Category("Behavior")>
    Public Property Value() As Long
        Get
            Return _Value
        End Get
        Set
            If Value > _Maximum Then
                Value = _Maximum
            End If
            _Value = Value
            Invalidate()
        End Set
    End Property
    <Description("Gets or Sets the Maximum Value of the Progress bar."), Category("Behavior")>
    Public Property Maximum() As Long
        Get
            Return _Maximum
        End Get
        Set
            If Value < 1 Then
                Value = 1
            End If
            _Maximum = Value
            Invalidate()
        End Set
    End Property
    <Description("Initial Color of Progress Bar"), Category("Appearance")>
    Public Property BarColor1() As Color
        Get
            Return _ProgressColor1
        End Get
        Set
            _ProgressColor1 = Value
            Invalidate()
        End Set
    End Property
    <Description("Final Color of Progress Bar"), Category("Appearance")> 
    Public Property BarColor2() As Color
        Get
            Return _ProgressColor2
        End Get
        Set
            _ProgressColor2 = Value
            Invalidate()
        End Set
    End Property
    <Description("Progress Bar Width"), Category("Appearance")>
    Public Property BarWidth() As Single
        Get
            Return _BarWidth
        End Get
        Set
            _BarWidth = Value
            Invalidate()
        End Set
    End Property
    <Description("Modo del Gradiente de Color"), Category("Appearance")>
    Public Property GradientMode() As LinearGradientMode
        Get
            Return _GradientMode
        End Get
        Set
            _GradientMode = Value
            Invalidate()
        End Set
    End Property
    <Description("Color de la Linea Intermedia"), Category("Appearance")>
    Public Property LineColor() As Color
        Get
            Return _LineColor
        End Get
        Set
            _LineColor = Value
            Invalidate()
        End Set
    End Property
    <Description("Width of Intermediate Line"), Category("Appearance")>
    Public Property LineWidth() As Integer
        Get
            Return _LineWitdh
        End Get
        Set
            _LineWitdh = Value
            Invalidate()
        End Set
    End Property
    <Description("Get or Set the Shape of the progress bar terminals."), Category("Appearance")>
    Public Property ProgressShape() As _ProgressShape
        Get
            Return ProgressShapeVal
        End Get
        Set
            ProgressShapeVal = Value
            Invalidate()
        End Set
    End Property
    <Description("Modo del Gradiente de Color"), Category("Appearance")>
    Public Property ShadowOffset() As Integer
        Get
            Return _ShadowOffset
        End Get
        Set
            If Value > 2 Then
                Value = 2
            End If
            _ShadowOffset = Value
            Invalidate()
        End Set
    End Property
    <Description("Get or Set the Mode as the Text is displayed inside the Progress bar."), Category("Behavior")>
    Public Property TextMode() As _TextMode
        Get
            Return ProgressTextMode
        End Get
        Set
            ProgressTextMode = Value
            Invalidate()
        End Set
    End Property
    Protected Overloads Overrides Sub OnResize(e As EventArgs)
        MyBase.OnResize(e)
        SetStandardSize()
    End Sub
    Protected Overloads Overrides Sub OnSizeChanged(e As EventArgs)
        MyBase.OnSizeChanged(e)
        SetStandardSize()
    End Sub
    ' 重写背景绘制，不调用基类实现
    Protected Overloads Overrides Sub OnPaintBackground(p As PaintEventArgs)
        ' 空实现，避免默认绘制背景
    End Sub
    Private Sub SetStandardSize()
        Dim _Size As Integer = Math.Max(Width, Height)
        Size = New Size(_Size, _Size)
    End Sub
    Public Sub Increment(Val As Integer)
        _Value += Val
        Invalidate()
    End Sub
    Public Sub Decrement(Val As Integer)
        _Value -= Val
        Invalidate()
    End Sub
    Protected Overrides Sub OnPaint(e As PaintEventArgs)
        Using bitmap As New Bitmap(Width, Height)
            Using graphics As Graphics = Graphics.FromImage(bitmap)
                graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear
                graphics.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality
                graphics.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality
                graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias
                graphics.TextRenderingHint = Drawing.Text.TextRenderingHint.AntiAliasGridFit
                
                ' 绘制父控件背景实现透明
                PaintTransparentBackground(Me, graphics)
                
                Dim rect As Rectangle = New Rectangle(10, 10, MyBase.Width - 20, MyBase.Width - 20)
                
                ' 仅当背景不透明时绘制中间椭圆
                If Not BackColor = Color.Transparent Then
                    Using mBackColor As Brush = New SolidBrush(BackColor)
                        graphics.FillEllipse(mBackColor, rect)
                    End Using
                End If
                
                Using pen2 As New Pen(LineColor, LineWidth)
                    graphics.DrawEllipse(pen2, rect)
                End Using
                Using brush As New LinearGradientBrush(ClientRectangle, _ProgressColor1, _ProgressColor2, GradientMode)
                    Using pen As New Pen(brush, BarWidth)
                        Select Case ProgressShapeVal
                            Case _ProgressShape.Round
                                pen.StartCap = LineCap.Round
                                pen.EndCap = LineCap.Round
                                Exit Select
                            Case _ProgressShape.Flat
                                pen.StartCap = LineCap.Flat
                                pen.EndCap = LineCap.Flat
                                Exit Select
                        End Select
                        graphics.DrawArc(pen, rect, -90, CType((360 / _Maximum) * _Value, Integer))
                    End Using
                End Using

                Select Case TextMode
                    Case _TextMode.None
                        Text = String.Empty
                        Exit Select
                    Case _TextMode.Value
                        Text = _Value.ToString()
                        Exit Select
                    Case _TextMode.Percentage
                        Text = Convert.ToString((100 / _Maximum) * _Value) & "%"
                        Exit Select
                    Case _TextMode.Custom
                        Text = Text
                        Exit Select
                    Case Else
                        Exit Select
                End Select

                If Text IsNot String.Empty Then
                    Dim MS As SizeF = graphics.MeasureString(Text, Font)
                    Dim shadowBrush As New SolidBrush(Color.FromArgb(100, ForeColor))
                    If ShadowOffset > 0 Then graphics.DrawString(Text, Font, shadowBrush, (Width / 2 - MS.Width / 2) + ShadowOffset, (Height / 2 - MS.Height / 2) + ShadowOffset)
                    graphics.DrawString(Text, Font, New SolidBrush(ForeColor), (Width / 2 - MS.Width / 2), (Height / 2 - MS.Height / 2))
                End If
                
                e.Graphics.DrawImage(bitmap, 0, 0)
            End Using
        End Using
    End Sub
    ' 修改方法参数，使用绘制位图的Graphics对象
    Private Shared Sub PaintTransparentBackground(c As Control, g As Graphics)
        If c.Parent Is Nothing OrElse Not Application.RenderWithVisualStyles Then
            Return
        End If
        ButtonRenderer.DrawParentBackground(g, c.ClientRectangle, c)
    End Sub

    Private Sub FillCircle(g As Graphics, brush As Brush, centerX As Single, centerY As Single, radius As Single)
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear
        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality
        g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias
        Using gp As New System.Drawing.Drawing2D.GraphicsPath()
            g.FillEllipse(brush, centerX - radius, centerY - radius, radius + radius, radius + radius)
        End Using
    End Sub
End Class

内容的提问来源于stack exchange，提问作者HomeCoder