How to Set WinForms Textbox to overwrite mode

Question

Is it possible to force a textbox in a windows forms application to work in "overwrite mode", i.e. have characters replaced when the user types instead of added?
Otherwise, is there a standard way to get this behavior?

Answer 1

Try using a MaskedTextBox and set InsertKeyMode to InsertKeyMode.Overwrite.

MaskedTextBox box = ...;
box.InsertKeyMode = InsertKeyMode.Overwrite;

Answer 2

If you do not wish to use a Masked textbox you can do this when handling the KeyPress event.

    private void Box_KeyPress(object sender, KeyPressEventArgs e)
    {
        TextBox Box = (sender as TextBox);
        if (Box.SelectionStart < Box.TextLength && !Char.IsControl(e.KeyChar))
        {
            int CacheSelectionStart = Box.SelectionStart; //Cache SelectionStart as its reset when the Text property of the TextBox is set.
            StringBuilder sb = new StringBuilder(Box.Text); //Create a StringBuilder as Strings are immutable
            sb[Box.SelectionStart] = e.KeyChar; //Add the pressed key at the right position
            Box.Text = sb.ToString(); //SelectionStart is reset after setting the text, so restore it
            Box.SelectionStart = CacheSelectionStart + 1; //Advance to the next char
        }
    }

Answer 3

Standard way would be to select the existing text as you land in the textbox, then as the user types it will automatically replace the existing text

Answer 4

This code seems to have an error. I found that you need to set e.Handled in the Keypress event, otherwise the character is inserted twice. Here is my code (in VB) based on the above: -

Private Sub txtScreen_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtScreen.KeyPress
    If txtScreen.SelectionStart < txtScreen.TextLength AndAlso Not [Char].IsControl(e.KeyChar) Then
        Dim SaveSelectionStart As Integer = txtScreen.SelectionStart
        Dim sb As New StringBuilder(txtScreen.Text)
        sb(txtScreen.SelectionStart) = e.KeyChar
        'Add the pressed key at the right position
        txtScreen.Text = sb.ToString()
        'SelectionStart is reset after setting the text, so restore it
        'Advance to the next char
        txtScreen.SelectionStart = SaveSelectionStart + 1
        e.Handled = True
    End If
End Sub