处理VScrollbar Paint事件 [英] Handling VScrollbar Paint event

问题描述

我一直在尝试为表单上的控件处理Paint事件.但是，该事件从未得到处理，而且我不确定自己在做什么错.我创建了一个非常简单的WinForms项目来演示这一点(我包括了生成的设计器代码，以表明那里什么都没有了):

I've been trying to handle the Paint event for a control on a form. However the event never gets handled, and I'm not sure what I'm doing wrong. I've created a very simple WinForms project to demonstrate this (I've included the generated designer code to show that there's nothing else there):

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

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

该事件永远不会被处理，但是控件是正确绘制的.我想念什么?

The event is never handled, but the control is drawn correctly. What am I missing?

推荐答案

好吧，在花了更多时间之后，我发现您需要做的就是调用

Well, after spending a bit more time on this, I've discovered that all you need to do is call the SetStyle() method with the flag and value parameters set to ControlStyles.userPaint and True, respectively.

该方法不是公开的，因此需要反射才能调用它:

This method isn't public though, so reflection is needed in order to invoke it:

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

我将上面的代码放在上面的Form1_Load方法中，恰好在AddHandler行的上方，并且似乎可以正常工作(我可以处理该事件).

I put the above code into the Form1_Load method above, just above the AddHandler line and it appears to work (I can handle the event).

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