Allow only numeric entry in WPF Text Box

We can do validation on text box changed event. The following implementation prevents keypress input other than numeric and one decimal point.

private void textBoxNumeric_TextChanged(object sender, TextChangedEventArgs e)
{
        TextBox textBox = sender as TextBox;
        Int32 selectionStart = textBox.SelectionStart;
        Int32 selectionLength = textBox.SelectionLength;
        String newText = String.Empty;
        int count = 0;
        foreach (Char c in textBox.Text.ToCharArray())
        {
            if (Char.IsDigit(c) || Char.IsControl(c) || (c == '.' && count == 0))
            {
                newText += c;
                if (c == '.')
                    count += 1;
            }
        }
        textBox.Text = newText;
        textBox.SelectionStart = selectionStart <= textBox.Text.Length ? selectionStart : textBox.Text.Length;    
}

Another way is simply to not allow values that are not integers. The following implementation is a little bit sucky, and I would like to abstract it later on in order for it to be more reusable, but here is what I did:

in the code behind in my view (I know this is might hurt if you are a hardcore mvvm ;o) ) I defined the following functions :

  private void NumericOnly(System.Object sender, System.Windows.Input.TextCompositionEventArgs e)
{
    e.Handled = IsTextNumeric(e.Text);

}


private static bool IsTextNumeric(string str)
{
    System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex("[^0-9]");
    return reg.IsMatch(str);

}

And in the XAML view, every textbox that was only supposed to accept integers was defined like this:

   <TextBox Padding="2"  TextAlignment="Right" PreviewTextInput="NumericOnly" Text="{Binding xxx.yyyy}" MaxLength="1" />

The key attribute being PreviewTextInput

The red border you've seen is actually a ValidationTemplate, which you can extend and add a info for the user. See this example:

    <UserControl.Resources>
        <ControlTemplate x:Key="validationTemplate">
            <Grid>
                <Label Foreground="Red" HorizontalAlignment="Right" VerticalAlignment="Center">Please insert a integer</Label>
                <Border BorderThickness="1" BorderBrush="Red">
                    <AdornedElementPlaceholder />
                </Border>
            </Grid>
        </ControlTemplate>
    </UserControl.Resources>

<TextBox Name="tbValue" Validation.ErrorTemplate="{StaticResource validationTemplate}">