Question

I am trying to make a Numeric only TextBox in WPF and I have this code for it:

void NumericTextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    e.Handled = !IsValidInput(e.Text);
}

private bool IsValidInput(string p)
{
    switch (this.Type)
    {
        case NumericTextBoxType.Float:
            return Regex.Match(p, "^[0-9]*[.][0-9]*$").Success;
        case NumericTextBoxType.Integer:                    
        default:
            return Regex.Match(p, "^[0-9]*$").Success;                    
    }
}

// And also this!
public enum NumericTextBoxType
{
    Integer = 0, 
    Float = 1
}

When I set the type to Integer, it works well, but for Float, it does not.

I can use so many NumericTextBox controls out there, but I was wondering why this one is not working?

Answer 1

Try this:

@"^[0-9]*(?:\.[0-9]*)?$"

You need to escape the period. And making the period and decimal part optional is probably a good idea.

If you need to handle negative values you can add -? before the first [0-9] in each pattern.

Update

Tested as follows:

var regex = new Regex(@"^[0-9]*(?:\.[0-9]*)?$");
Console.WriteLine(new bool[] {regex.IsMatch("blah"),
                              regex.IsMatch("12"),
                              regex.IsMatch(".3"),
                              regex.IsMatch("12.3"),
                              regex.IsMatch("12.3.4")});

results in

False 
True 
True 
True 
False