从TextBox继承的vb .NET自定义控件不会触发Paint事件 [英] vb .NET custom control inheriting from TextBox doesn't fire Paint event

问题描述

我需要一个多行文本框，该框始终处于禁用状态，但不应将其自身涂成灰色，但我想保留其设计者选择的颜色。

I need a multiline TextBox which is always disabled, but it shouldn't paint itself in gray, but I want to keep its designer choosen color.

我以前对始终为黑色的Label（没有多行）有相同的要求，所以我从Label继承来了：

I previously had the same requirement with an always-black Label (no multiline) and so I inherited from Label like:

Imports System.ComponentModel

   Public Class LabelDisabled
        Inherits Label

        Sub New()
            InitializeComponent()
            Enabled = False
        End Sub

        Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
            ' always draw it black
            e.Graphics.DrawString(Me.Text, Me.Font, Brushes.Black, 0, 0)
        End Sub

    End Class

这很好。现在我想要相同的东西，但是带有多行标签，所以我选择从TextBox继承：

That works fine. Now I want the same thing but with a multiline label, so I chose to inherit from TextBox:

Imports System.ComponentModel

Public Class CustomControl1
    Inherits TextBox

    Sub New()

        InitializeComponent()
        'Paint never fires anyway
        'Enabled = False
    End Sub


    Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
        Dim brush As New SolidBrush(Me.ForeColor)
        e.Graphics.DrawString(Me.Text, Me.Font, brush, 0, 0)
    End Sub

End Class

现在，永远不会在CustomControl1-TextBox继承-控件中触发Paint事件。

Now the Paint event is never fired in the CustomControl1 - TextBox inherited - control.

为什么不能获得Paint事件？

Why can't I get the Paint event?

此外，如果我想使Enabled属性不可见且用户无法设置，我会做：

Also, if I want to make the Enabled property invisible and not-settable by the user, I do:

<Browsable(False),
DefaultValue(False)>
Public Overloads Property Enabled As Boolean
    Get
        Return False
    End Get
    Set(ByVal value As Boolean)
    End Set
End Property

但是这样，我都不能设置 real Enabled属性，我的意思是后备字段。

But this way, neither I can set the "real" Enabled property, I mean the backing field.

推荐答案

我找到了一个解决方案。看起来TextBox甚至禁用了子类的Paint事件。但是您可以强制WM_PAINT位调用SetStyle：

I've found a solution. It looks like a TextBox disables the Paint event even for subclasses. But you can force the WM_PAINT bit calling SetStyle:

Public Class DisabledTextBox
    Inherits TextBox

    Public Sub New()
        InitializeComponent()

        Enabled = False
        SetStyle(ControlStyles.Selectable, False)
        SetStyle(ControlStyles.UserPaint, True)

    End Sub

    Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
        Dim brush As New SolidBrush(Me.ForeColor)
        e.Graphics.DrawString(Me.Text, Me.Font, brush, 0, 0)
    End Sub

End Class

它可以按预期的那样完美运行：）

It works perfectly as expected :)

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