C#

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool ShowScrollBar(IntPtr hWnd, int wBar, [MarshalAs(UnmanagedType.Bool)] bool bShow);

User-Defined Types:

None.

Notes:

For reference:

SB_HORZ = 0

SB_VERT = 1

SB_CTL = 2

SB_BOTH = 3

Tips & Tricks:

Please add some!

Sample Code:

Please add some!

Alternative Managed API:

Do you know one? Please contribute it!

VB Signature:

Private Declare Function ShowScrollBar Lib "user32" (ByVal hwnd As Long, ByVal wBar As Long, ByVal bShow As Long) As Long

Tips & Tricks:

http://www.vb-helper.com/howto_show_hide_text_scrollbar.html

http://www.vb-helper.com/howto_show_hide_both_scrollbars.html

Sample Code:

When the form loads, set a hidden PictureBox's Font property to match the TextBox's.

In the TextBox's Change event handler, use the PictureBox's TextHeight function to see how tall the text is. If the text is too big to fit in the TextBox, we need to display the scrollbar. If the need for the scrollbar has changed, use the ShowScrollBar API function to show or hide it.

Private m_ScrollBarVisible As Boolean

Private Declare Function ShowScrollBar Lib "user32" (ByVal _

    hwnd As Long, ByVal wBar As Long, ByVal bShow As Long) _
    As Long

Private Const SB_VERT = 1

Private Sub Form_Load()

    ' Make picHidden use the TextBox's font.
    picHidden.Font = txtValue.Font

    ' Perform the initial startup check.
    txtValue_Change

End Sub

Private Sub txtValue_Change()

Dim needs_scrollbar As Boolean

    ' See if we need the scrollbar.
    needs_scrollbar = _
    picHidden.TextHeight(txtValue.Text) > _
    txtValue.Height - 60

    ' See if the need has changed.
    If needs_scrollbar <> m_ScrollBarVisible Then
    ' Show or hide the scrollbar.
    m_ScrollBarVisible = needs_scrollbar
    ShowScrollBar txtValue.hwnd, SB_VERT, _
        m_ScrollBarVisible
    End If

End Sub