Help with regular expression for negative real numbers.

I would like to make a regular expression that limits the textboxes I have to negative real numbers. Unfortunately, the best I have been able to do is to limit the text box to numbers only. I have tried several "working" examples from around the web, but none of them worked for me. Here is my code based on my book and how I would think I should build the regular expression.

using System.Text.RegularExpressions;
using System.Windows;
using System.Windows.Input;
namespace WPF_Test_Unit
{
///
/// Interaction logic for MainWindow.xaml
///
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.SizeToContent = SizeToContent.WidthAndHeight;
}
private void CheckForNumber(object sender, TextCompositionEventArgs e)
{
Regex regex = new Regex(@"\-?\d+\.?\d+");
e.Handled = !regex.IsMatch(e.Text);
}
}
}

My idea is that I would need 0 or 1 negative sign "-", then one or more digits, an optional decimal "." and then one or more digits trailing the decimal point.

Below is the XAML that uses the function.

<TextBox Grid.Row="3" Grid.Column="1" VerticalAlignment="Center" PreviewTextInput="CheckForNumber" HorizontalAlignment="Center" FontSize="20" Width="170" Height="40" />

I have tried many combinations of regular expressions, but the only results I can get with preventing characters in the textbox a numbers-only situation. Trying to remove (or allow) other characters seems not to work.

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Nilesh Sawardekar7y ago
Try this code in text box validated or key down ...not in key press...
Nilesh Sawardekar7y ago
below link may help you,

https://stackoverflow.com/questions/17466575/negative-numbers-in-c-sharp-textbox
Nilesh Sawardekar7y ago
Can you provide exact number samples which you are looking for as output?
Željko Perić7y ago
Hello https://www.c-sharpcorner.com/members/boris-g,

I think that this is correct regular expression : ^\-\d+\.\d+$
that will find match only to negative real numbers.

This would be any positive or negative real number : ^[\+|\-]?\d+\.\d+$

And this would be correct regex for above special case : ^[\+|\-]?\d+(\.\d+$)*

I think that there is problem with line 21.

perhaps it should look like this :
e.Handled = regex.IsMatch(e.Text);
All the best,
Željko Peric