Question

I will like to validate user entry to ensure they are integers. How can I do it? I thought of using IDataErrorInfo which seems like the “correct” way to do validation in WPF. So I tried implementing it, in my ViewModel.

But the thing is my text box is bound to an integer field, and there isn’t any need to validate if an int is an int. I noticed that WPF automatically adds a red border around the textbox to notify the user of the error. The underlying property doesn’t change to an invalid value. But I would like to notify the user of this. How can I do it?

Answer 1

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}">