Question

In my application I am using RichTextBoxes with readonly property set to True.
But the font size can still be changed using the mouse wheel and default windows keyboard shortcut for fontsize change (Ctrl+shift+ >/<).

How do I disable RichTextBox font size change?

Answer 1

To disable the key combinations of Control+Shift+< or Control+Shift+>, you need to implement the following KeyDown event handler for your RichTextBox control:

 Private Sub RichTextBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles RichTextBox1.KeyDown

    ' disable the key combination of 
    '     "control + shift + <" 
    '     or
    '     "control + shift + >"
    e.SuppressKeyPress = e.Control AndAlso e.Shift And (e.KeyValue = Keys.Oemcomma OrElse e.KeyValue = Keys.OemPeriod)

End Sub

This code prevents the user from resizing the font in the given RichTextBox with keyboard commands.

To disable changing the font size by using Ctrl plus the mousewheel, the only way I know how to do this is to make a user control that inherits from RichTextBox.

Once you have done that the only thing you need to do is override the WndProc procedure so that it effectively disables any messages when the scrollwheel is moving and the Ctrl button is pressed. See the code below for implementing a UserControl derived from the RichTextBox:

Public Class DerivedRichTextBox
    Inherits RichTextBox

    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

        ' windows message constant for scrollwheel moving
        Const WM_SCROLLWHEEL As Integer = &H20A

        Dim scrollingAndPressingControl As Boolean = m.Msg = WM_SCROLLWHEEL AndAlso Control.ModifierKeys = Keys.Control

        'if scolling and pressing control then do nothing (don't let the base class know), 
        'otherwise send the info down to the base class as normal
        If (Not scrollingAndPressingControl) Then

            MyBase.WndProc(m)

        End If


    End Sub

End Class