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| Title | Restrict a TextBox to at most four lines using the KeyPress event |
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| Keywords | TextBox, restrict, lines, carriage return |
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| Categories | Controls |
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In the KeyPress event handler, see what the user is typing. If it is a carriage return, see how many lines the new value would have. If it would have more than four lines, set KeyAscii = 0 to disallow the new character.
If the user types Control-V, see what the new value would be after pasting the clipboard's contents. If the new value has more than four lines, set KeyAscii = 0 to disallow the new character.
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Private Sub txtFourLines_KeyPress(KeyAscii As Integer)
Const ASC_CR = 13 ' ASCII value of vbCr.
Const CTL_V = 22 ' ASCII value of Control-V.
Dim new_value As String
' See what the user is typing.
If KeyAscii = ASC_CR Then
' Carriage return.
' See if the text already contains
' more than 3 lines. Remember Split
' returns a zero-based array so UBound
' returns 1 less than the count.
If UBound(Split(txtFourLines.Text, vbCr)) > 2 Then
' Disallow this character.
KeyAscii = 0
End If
ElseIf KeyAscii = CTL_V Then
' Control-V.
' See what the new value will be.
new_value = _
Left$(txtFourLines.Text, txtFourLines.SelStart) _
& _
Clipboard.GetText & _
Mid$(txtFourLines.Text, txtFourLines.SelStart + _
txtFourLines.SelLength + 1)
' See how many lines this would be.
If UBound(Split(new_value, vbCr)) > 3 Then
' Disallow this character.
KeyAscii = 0
End If
End If
End Sub
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Note that the user could still use the TextBox's popup menu to paste text. To prevent that, subclass the TextBox and intercept the WM_CONTEXTMENU message.
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