Using + (plus) and - (minus) keyboard keys as incrementors and decrementors in a DataGridView

Question

Hello,

On a WinForms application that I am writing in C#, I have a DataGridViewTextBoxColumn with cells holding integer values that I would like the users to be able to increment or decrement using the + and - keys from their keyboards.

I've handled the KeyDown event as it is what I use usually to handle Delete keys, etc, but it isn't working for Plus and Minus keys as pressing them causes the Cell to go in Edit-mode, and the KeyDown event is never fired for those keys as a result. Same for the KeyPress event

Actually, it is fired if I set the cells to readonly, but I am not happy with this solution as it would force me to set the property from true to false in several areas of my code and could quickly become messy.

What would please be the best way to achieve this?

Thanks.

Answer 1

You need to trap the keystroke before they get to the datagrid.

This looks suprisingly close to what you're trying to do: http://support.microsoft.com/kb/320584

Answer 2

Wow, that KB article is pretty bad. That should be done by overriding IsInputKey().

I don't care much for DGV, it is a bugger to customize. But you can probably whack this into some kind of shape:

using System;
using System.Windows.Forms;

class MyDgv : DataGridView {
    public event EventHandler Increment;
    public event EventHandler Decrement;

    protected override void OnKeyDown(KeyEventArgs e) {
        bool used = false;
        if (this.EditingControl == null) {
            if (e.KeyData == Keys.Oemplus) {
                if (Increment != null) { Increment(this, EventArgs.Empty); used = true; }
            }
            else if (e.KeyData == Keys.OemMinus) {
                if (Decrement != null) { Decrement(this, EventArgs.Empty); used = true; }
            }
        }
        if (used) e.SuppressKeyPress = e.Handled = true;
        else base.OnKeyDown(e);
    }
}