从 TextBox 继承的 vb .NET 自定义控件不会触发 Paint 事件

Question

我需要一个始终禁用的多行文本框，但它不应该将自身涂成灰色，但我想保持其设计者选择的颜色。

我以前对始终为黑色的标签（没有多行）有相同的要求，所以我从标签继承如下：

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

效果很好。现在我想要同样的东西，但有一个多行标签，所以我选择从 TextBox 继承：

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

现在在 CustomControl1 - TextBox 继承 - 控件中永远不会触发 Paint 事件。

为什么我无法获得 Paint 事件？

另外，如果我想让 Enabled 属性对用户不可见且不可设置，我会这样做：

<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，我也不能设置“真正的”启用属性，我的意思是支持字段。

Answer 1

我找到了解决方案。看起来 TextBox 甚至对子类也禁用了 Paint 事件。但是你可以强制 WM_PAINT 位调用 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

它按预期完美运行:)

Answer 2

这是你的答案：

Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
    MyBase.OnPaint(e)
    e.Graphics.FillRectangle(Brushes.LightGray, Me.DisplayRectangle)
    Dim sf As New StringFormat
    sf.FormatFlags = StringFormatFlags.NoWrap
    sf.HotkeyPrefix = Drawing.Text.HotkeyPrefix.Show 'if Mnemonic property is set to true
    sf.HotkeyPrefix = Drawing.Text.HotkeyPrefix.Hide 'or none if Mnemonic property is set to false
    sf.LineAlignment = StringAlignment.Center 'horizontal alignment
    sf.Alignment = StringAlignment.Center ' vertical ...
    Dim rect As Rectangle = Me.DisplayRectangle ' this is your text bounds for setting your text alignement using StringFormat(sf)
    e.Graphics.DrawString("Something", Me.Font, Brushes.DarkOliveGreen, rect, sf)
End Sub