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KeyDown event - how to easily know if the key pressed is numeric?

Answer 1

A:

On the msdn help page they use this code in their example:

// Determine whether the keystroke is a number from the top of the keyboard.
if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)

...

// Determine whether the keystroke is a number from the keypad.
if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)

tanascius 2010-07-01 11:05:59

@Rawling, @tanascius: thanks, I did think about that but I thought that it was a bad practice to perform range evaluations against enumerations?I agree that the fact that it comes from MSDN makes it relatively safe, but after all, it wouldn't be the first time we would see bad example code from MSDN...Is there anything that guarantees that the values will always be contiguous? After all, we have enumerations so to not rely on the underlying values? By performing such a check, am I not relying on the fact that these enumerations values will be contiguous to each other? Thanks.

Kharlos Dominguez 2010-07-01 11:10:28

As bad as a practice as that may be, I would hope that since Microsoft is using that in their docs, they would be careful to keep the behavior consistent. If you can switch to the KeyPress event instead of KeyDown, you can use the solution I provided.

Tim Coker 2010-07-01 11:12:19

Yeah, if there's a reason not to do that, Tim's solution is good - and makes it a lot more obvious what you're trying to do, too.

Rawling 2010-07-01 11:15:32

@Kharlos: I understand the issues you have, but think about what they would have to change to make your code break. The enum can change without any problem as long as they do not change the order of the *NumPad?* and *D?* elements. And I think that there is no reason to define *NumPad9* before *"NumPad8* ...

tanascius 2010-07-01 11:19:05

Yeah, I agree with you that is very unlikely that they would do that. It is more a rhetorical issue than a real-world one, but if I can, I might as well not try to break a best practice, even if it is unlikely it would pose any problem in the real-world.

Kharlos Dominguez 2010-07-01 11:34:19

Answer 2

+3 A:

Try

if ((e.KeyCode >= Keys.D0 && e.KeyCode <= Keys.D9) ||
    (e.KeyCode >= Keys.NumPad0 && e.KeyCode <= Keys.NumPad9) ||
    e.KeyCode == Keys.Decimal)
{
    // Edit mode
}

Rawling 2010-07-01 11:06:30

Answer 3

+4 A:

If you use the KeyPress event, the event signature has a KeyPressEventArgs with a KeyChar member that gives you the character for the numberpad keys. You can do a TryParse on that to figure out if its a number or not.

private void Form1_KeyPress(object sender, KeyPressEventArgs e)
{
    int i;
    if (int.TryParse(e.KeyChar.ToString(), out i))
    {
        MessageBox.Show("Number");
    }
}

Tim Coker 2010-07-01 11:10:37

Or even e.KeyChar.IsDigit()?

Rawling 2010-07-01 11:12:52

Thanks Tim and Rawling. That's the solution I went with. I also have to handle a DEL key event in KeyDown... I would have preferred to keep it all at the same spot, but this code looks by far the nicest. Thanks everyone else as well.

Kharlos Dominguez 2010-07-01 11:31:07

Answer 4

A:

void dataGridView1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e) { // Used this to find they key values. //label1.Text += e.KeyValue;

        // Check if key is numeric value.
        if((e.KeyValue >= 48 && e.KeyValue <= 57) || (e.KeyValue >= 97 && e.KeyValue <= 105))
            System.Console.WriteLine("Pressed key is numeric");
    }

MrFox 2010-07-01 11:16:44

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KeyDown event - how to easily know if the key pressed is numeric?

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