Help with regular expression for negative real numbers.

Question

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
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    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.