Using a wizard in my application that validates the input. The user must not be able to move to the next page if the validation is not a success. This can be done by disabling the next button when validation failes. The NextButtonEnabled property is hooked to the Validation.HasError property of the inputcontrol. Code sample below.

<wizard:WizardPage x:Name="WizardPage">
    <!--Style that sets the NextButtonEnabled based on validation-->            
    <wizard:WizardPage.Style>
        <Style TargetType="wizard:WizardPage">
            <Style.Triggers>
                <DataTrigger Binding="{Binding ElementName=DataControl,Path=(Validation.HasError), UpdateSourceTrigger=PropertyChanged}" Value="True">
                    <Setter Property="NextButtonEnabled" Value="False" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </wizard:WizardPage.Style>
    <!--Input controls-->
    <AdornerDecorator>
        <TextBox Name="DataControl">
            <TextBox.Text>
                <Binding Path="MyValue" UpdateSourceTrigger="PropertyChanged" >
                    <Binding.ValidationRules>
                        <my:NotNullOrEmptyValidationRule ErrorMessage="Supply data"/>
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>
    </AdornerDecorator>
</wizard:WizardPage>

This doesn’t cover the user directly clicking the next button, but that is handled by the check in the Unselecting eventhandler.