NumericTextBox

The NumericTextBox behavior makes it easy to allow specific numeric input on a TextBox.

1) Add the following XML namespaces:

xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
xmlns:catel="http://catel.codeplex.com"

2) Use the following definition:

<TextBox Text={Binding Amount}">
    <i:Interaction.Behaviors>
        <catel:NumericTextBox />
    </i:Interaction.Behaviors>
</TextBox>

Use the properties on the behavior to customize the behavior to your needs