处理滚动条绘制事件

Question

我一直在尝试处理Paint事件的窗体上的控件。然而，这个事件从来没有得到处理，我不确定我做错了什么。我创建了一个非常简单的WinForms项目来演示这一点(我包含了生成的设计器代码，以显示没有其他内容):

Form1.vb

Public Class Form1
    Private Sub Form1_Load( sender As Object,  e As EventArgs) Handles MyBase.Load
        AddHandler VScrollBar1.Paint, AddressOf VScrollBar1_Paint
    End Sub
    Private Sub VScrollBar1_Paint (ByVal sender As Object, ByVal e As PaintEventArgs)
        Dim str As String = "test"
        System.Windows.Forms.MessageBox.Show(str)
    End Sub                              
End Class

Form1.Designer.vb

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form
    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub
    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer
    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.VScrollBar1 = New System.Windows.Forms.VScrollBar()
        Me.SuspendLayout
        '
        'VScrollBar1
        '
        Me.VScrollBar1.Location = New System.Drawing.Point(26, 56)
        Me.VScrollBar1.Name = "VScrollBar1"
        Me.VScrollBar1.Size = New System.Drawing.Size(17, 80)
        Me.VScrollBar1.TabIndex = 0
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6!, 13!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(284, 261)
        Me.Controls.Add(Me.VScrollBar1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(false)
    End Sub
        Friend WithEvents VScrollBar1 As System.Windows.Forms.VScrollBar
End Class

事件永远不会被处理，但是控件被正确绘制。我错过了什么?

Answer 1

好吧，花了一点时间在这之后，我发现所有你需要做的就是调用SetStyle()方法与标志和值参数分别设置为ControlStyles.userPaint和True。

这个方法不是公共的，所以需要反射来调用它:

Dim methodInfo As System.Reflection.MethodInfo = VScrollBar1.GetType().GetMethod("SetStyle", Reflection.BindingFlags.Instance Or Reflection.BindingFlags.NonPublic)
methodInfo.Invoke(VScrollBar1, {ControlStyles.UserPaint, True})

我把上面的代码放入上面的Form1_Load方法中，就在AddHandler行上面，它似乎可以工作(我可以处理事件)。