如何在TextBox中允许并限制一个“。”（句点）字符？ （C＃Winforms）

Question

I have this code from MSDN that allows only numeric characters into a TextBox. But I can't modify it to accept a "." as an input and limit to one.

Ex: 12.50     valid!
    236.3247  valid!  
    2..5      invalid
    //other non-numeric input invalid

Considering the code below:

private bool nonNumberEntered = false;

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
    nonNumberEntered = false;

    if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
    {
        if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
        {
            if (e.KeyCode != Keys.Back)
            {
                nonNumberEntered = true;
            }
        }
    }
    if (Control.ModifierKeys == Keys.Shift)
    {
        nonNumberEntered = true;
    }
}

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (nonNumberEntered == true)
    {
        e.Handled = true;
    }
}

Kindly post your modified code. Thanks a lot.

Answer 1

I would just validate the field as a Culture-sensitive number after they tab off or on a form submit. It's not really necessary or valuable to actually stop them from pressing . twice in the field. Often I find that kind of thing annoying, because I'm modifying what was there and I just haven't finished...

Use double.TryParse to test it properly.

Answer 2

I have a textbox that I only want digits and commas in, so it's similar to what you have.

I'd just run a regex on textbox.Text to match digits and zero or one decimal points with each key press. If the string that would be created doesn't match, then just disallow that character.

I think a .NET example is "^\\d*.?\\d*$"

From left to right:

• ^ at the beginning of the string
• \\d* zero or more digits
• .? zero or one period
• \\d* zero or more digits
• $ end of string

Not exactly what you have above but that would work.