Highlight scroll bar of textbox [duplicate] - vb.net

Question

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?

Answer 1

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

Answer 2

Thanks dummy, it works! Here short version of dummy answer in c#
Call this code at the end of your SizeChanged and TextChanged handlers:
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.
}

Answer 3

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

Answer 4

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

Answer 5

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:
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.