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

Question

I am currently handling the KeyDown event of a DataGridView control. One of the columns is filled by calculated values and I want the user to be able to override the cell value if they want.

When the user presses a numeric key, the cell goes into EditMode and allows the user to override the value. If the key is not numeric, nothing happens...

That is working pretty well... the problem is that I find the code for it ugly... I can't seem to find a neat way to handle all the numeric keys in a single condition, so I've made a switch case construct to deal with all the possible numeric keys, like this:

                switch (e.KeyCode)
                {
                    case Keys.D0:
                    case Keys.D1:
                    case Keys.D2:
                    case Keys.D3:
                    case Keys.D4:
                    case Keys.D5:
                    case Keys.D6:
                    case Keys.D7:
                    case Keys.D8:
                    case Keys.D9:
                    case Keys.Decimal:
                    case Keys.NumPad0:
                    case Keys.NumPad1:
                    case Keys.NumPad2:
                    case Keys.NumPad3:
                    case Keys.NumPad4:
                    case Keys.NumPad5:
                    case Keys.NumPad6:
                    case Keys.NumPad7:
                    case Keys.NumPad8:
                    case Keys.NumPad9:

                         [code to make the cell go to editMode, etc...]

Sure, it works, but there has to be a better and shorter way, right?

All I could find using Google is converting e.KeyCode to a char, but when using numeric keys, it goes gives letters even for the numeric values...

Thanks.

Answer 1

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");
    }
}

Answer 2

Try

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

Answer 3

Why use keycodes, when you can use this:

void Control_KeyPress(object sender, KeyPressEventArgs e)
    {

        if (Char.IsDigit(e.KeyChar))
        {
            //do something
        }
        else
        {
            //do something else
        }
    }

It's cleaner and even if microsoft decides to change all enums vlue, it still would work

Answer 4

Sorcerer86pt's solution was the simplest, however, when a user presses a control key, like backspace, then it breaks. To solve that problem, you can use the following snippet:

void KeyPress(object sender, KeyPressEventArgs e)
{    
    if(!Char.IsNumber(e.KeyChar) && !Char.IsControl(e.KeyChar))
    {
        //The char is not a number or a control key
        //Handle the event so the key press is accepted
        e.Handled = true;
        //Get out of there - make it safe to add stuff after the if statement
        return;
    }
    //e.Handled remains false so the keypress is not accepted
}

If you're using WPF, you might find that a TextBox doesn't have a KeyPressed event. To fix this, I used the following code.

void ValidateKeyPress(object sender, KeyEventArgs e)
{
    char keyPressed = WPFUtils.Interop.Keyboard.GetCharFromKey(e.Key);
    if (!Char.IsNumber(keyPressed) && !Char.IsControl(keyPressed))
    {
        //As above
        e.Handled = true;
        return;
    }
}

You may notice the weird function call WPFUtils.Interop.Keyboard.GetCharFromKey(e.Key) this is one of the useful functions I've collected. You can find it here.

Answer 5

Just get the last char from the Key that will be number if a number was pressed. This method works with KeyDown events not needing any other conditions.

Just call this static method and pass in the Key to check

public static bool IsNumber(Keys key)
{
  string num = key.ToString().Substring(key.ToString().Length - 1);
  Int64 i64;
  if (Int64.TryParse(num, out i64))
  {
    return true;               
  }
  return false;
}

Answer 6

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)

Answer 7

A bit more condensed version:

    private void KeyPress(object sender, KeyPressEventArgs e)
    {
        e.Handled = !Char.IsDigit(e.KeyChar); // only allow a user to enter numbers
    }

Answer 8

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");
}