当内容超出边界时在文本框中显示滚动条 C#

Display scroll bar in textbox when contents are beyond the bounds C#

提问by Anders

Is it possible to show/hide the scroll bar in a text box only when the line count in the text box is more than the number of lines displayed?

仅当文本框中的行数大于显示的行数时，是否可以在文本框中显示/隐藏滚动条？

采纳答案by Austin Salonen

Consider using the RichTextBox-- it has that behavior built in.

考虑使用RichTextBox——它内置了这种行为。

回答by dummy

Public Class TextBoxScrollbarPlugin
    Private WithEvents mTarget As TextBox

    ''' <summary>
    ''' After the Handle is created, mTarget.IsHandleCreated always returns
    ''' TRUE, even after HandleDestroyed is fired.
    ''' </summary>
    ''' <remarks></remarks>
    Private mIsHandleCreated As Boolean = False

    Public Sub New(item As TextBox)
        mTarget = item
        mIsHandleCreated = mTarget.IsHandleCreated
    End Sub

    Private Sub Update()
        If Not mTarget.IsHandleCreated Then
            Return
        ElseIf Not mIsHandleCreated Then
            Return
        End If
        Dim textBoxRect = TextRenderer.MeasureText(mTarget.Text,
                                                   mTarget.Font,
                                                   New Size(mTarget.Width, Integer.MaxValue),
                                                   TextFormatFlags.WordBreak + TextFormatFlags.TextBoxControl)

        Try
            If textBoxRect.Height > mTarget.Height Then
                mTarget.ScrollBars = ScrollBars.Vertical
            Else
                mTarget.ScrollBars = ScrollBars.None
            End If
        Catch ex As System.ComponentModel.Win32Exception
            'this sometimes throws a "failure to create window handle"
            'error.
            'This might happen if the TextBox is unvisible and/or
            'to small to display a toolbar.
            If mLog.IsWarnEnabled Then mLog.Warn("Update()", ex)
        End Try
    End Sub

    Private Sub mTarget_HandleCreated(sender As Object, e As System.EventArgs) Handles mTarget.HandleCreated
        mIsHandleCreated = True
    End Sub

    Private Sub mTarget_HandleDestroyed(sender As Object, e As System.EventArgs) Handles mTarget.HandleDestroyed
        mIsHandleCreated = False
    End Sub

    Private Sub mTarget_SizeChanged(sender As Object, e As System.EventArgs) Handles mTarget.SizeChanged
        Update()
    End Sub

    Private Sub mTarget_TextChanged(sender As Object, e As System.EventArgs) Handles mTarget.TextChanged
        Update()
    End Sub

End Class


Private mPlugins As New List(Of Object)
Private Sub Form_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    mPlugins.Add(New TextBoxScrollbarPlugin(txtBoxOne))
    mPlugins.Add(New TextBoxScrollbarPlugin(txtBoxTwo))
    mPlugins.Add(New TextBoxScrollbarPlugin(txtBoxThree))
End Sub  

回答by tnimas

Thanks dummy, it works! Here short version of dummy answer in c#

谢谢假人，它有效！这里是 C# 中虚拟答案的简短版本

Call this code at the end of your SizeChanged and TextChanged handlers:

在 SizeChanged 和 TextChanged 处理程序的末尾调用此代码：

Size textBoxRect = TextRenderer.MeasureText(
    this.YourTextBox.Text, 
    this.YourTextBox.Font, 
    new Size(this.YourTextBox.Width, int.MaxValue),
    TextFormatFlags.WordBreak | TextFormatFlags.TextBoxControl);
try
{
    this.YourTextBox.ScrollBars = textBoxRect.Height > this.YourTextBox.Height ? 
        ScrollBars.Vertical : 
        ScrollBars.None;
} catch (System.ComponentModel.Win32Exception)
{
     // this sometimes throws a "failure to create window handle" error.
     // This might happen if the TextBox is unvisible and/or
     // too small to display a toolbar.
}

回答by James Pusateri

I've got tnimas solution working in vb. Functions quite well as written and I've not seen the errors.

我有 tnimas 解决方案在 vb 中工作。函数写得很好，我没有看到错误。

    Private Sub TextBoxSizeChanged(sender As Object, e As EventArgs) Handles Me.SizeChanged
    Dim textBoxRect As Size = TextRenderer.MeasureText(TextBox.Text, TextBox.Font, New Size(TextBox.Width, Integer.MaxValue), TextFormatFlags.WordBreak Or TextFormatFlags.TextBoxControl)
    Try
        TextBox.ScrollBar = If(textBoxRect.Height > TextBox.Height, ScrollBars.Vertical, ScrollBars.None)
    Catch ex As Exception
        'handle error
    End Try
End Sub

回答by Pyon

I myself tried tnimas' solution but unable to catch the exception, so I use the WinApi to toggle the visible state of scrollbars instead like so:

我自己尝试了 tnimas 的解决方案，但无法捕获异常，所以我使用 WinApi 来切换滚动条的可见状态，而不是像这样：

Size textBoxRect = TextRenderer.MeasureText(YourTextBox.Text, YourTextBox.Font, new Size(YourTextBox.Width, int.MaxValue), TextFormatFlags.WordBreak | TextFormatFlags.TextBoxControl);

WinApi.ShowScrollBar(YourTextBox.Handle, (int)WinApi.ScrollBar.SB_VERT, textBoxRect.Height > YourTextBox.Height ? true : false);

This method does not cause the exception, though should note that hiding scrollbars like this will disable scroll messages, but this is fine if you're just hiding the scrollbars for when the text area can't be scrolled anyway.

此方法不会导致异常，但应注意，像这样隐藏滚动条将禁用滚动消息，但是如果您只是在文本区域无法滚动时隐藏滚动条，这很好。