Prevent users entering alphabetical characters but allow numerical and symbols-CodePudding

I've got a combo box that I want to allow users to enter in numerical digits, but not allow them to enter alphabetical characters.

My problem is that these numbers can be decimal so I need to allow the user to enter .

I've used char.IsSymbol but it doesn't seem to do what I want it to do.

private void DaySelection_ComboBox_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && !char.IsSymbol(e.KeyChar))
    {
        e.Handled = true;
    }
}

CodePudding user response：

Your best bet might be to have a specific list of allowed characters, and check against that. You can use a string for this for ease:

static readonly string _allowedNumericCharacters = "-0123456789.";

private void DaySelection_ComboBox_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!_allowedNumericCharacters.Contains(e.KeyChar))
    {
        e.Handled = true;
    }
}

Do you need the thousands separator? If so, you'll need to add , to the string.

Note that you might need to adjust that string for different locales. The decimal mark and the thousands separator is different for different locales.

CodePudding user response：

You could also use regex to do this, just something simple like

^[0-9.-]*$

This will just allow you to input any character between 0 and 9, a dot or a hyphen, then you just need to check if your string matches this. This should give the same result as the above answer.

Also I believe its better to test the whole string rather than an individual character upon a key press, this just adds extra protection for stuff like if they copy/paste text into the form