Question

I’m learning this wpf stuff and trying to get my head around validation of controls. Specifically what I’m looking for is this…

1. A form can have 100 controls on it (exaggerating, but possible). The form’s layout and flow are a specific order (via tabbed sequence for user). A user may never get to some “required” fields and click on a “Save” button. How can I trigger it so all the controls force triggering their own respective “Validation” events.

2. Based on above, does the WPF framework process the validation rules in the tab order the user is looking at. If not, how can that be controlled to match the data entry flow instead of bouncing around in the sequential order the application happens to create objects and their respective validation rules.

3. Is there a way to have ALL failed controls triggered for the default behavior of putting a red border box around the failed control instead of only one at a time.

Thanks

Answer 1

Typically, to accomplish what you are looking for you use an MVVM type pattern. This means that you bind each control that collects data in your WPF form to a backing field or property. You add validation to the binding, with a style that will cause the red border box. For controls with required data, part of the validation is that they are filled in. You could define a single validation rule for this called “ValidWhenHasData” or some such.

To cause the validations to trigger only when you press “save” or the like, there are a number of ways you can do this. I typically make a property in each validation rule called “IsEnabled” and set it to false by default; if set to false, the validation rule always returns valid. I then add a list in the code-behind of the controls that I want to validate. When “save” is clicked, I go through the list and set all the validation rules’ IsEnabled to true, clear all errors on the controls in the list, and then refresh the binding on each. This will display the red rectangles on any that are not filled in or whatever else you have defined as an error condition. You can also use this list to set focus to the first control that failed validation, in the order you choose.

Example validation control template, which includes placeholder for validation error tooltip:

<ControlTemplate x:Key="errorTemplate">
    <Canvas Width="{Binding Path=AdornedElement.ActualWidth, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Adorner}}}" Height="{Binding Path=AdornedElement.ActualHeight, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Adorner}}}">
        <Border BorderBrush="Red" BorderThickness="1">
            <AdornedElementPlaceholder/>
        </Border>
        <Border Canvas.Top="-5" Canvas.Right="-5" BorderBrush="Gray" BorderThickness="1" >
            <TextBlock x:Name="errorBlock" TextAlignment="Center" Background="Red" Foreground="White" Width="10" Height="10" FontSize="9" ctl:valTooltip.MessageBody="{Binding Path=AdornedElement.(Validation.Errors)[0].ErrorContent,RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Adorner}}}">*</TextBlock>
        </Border>
    </Canvas>
</ControlTemplate>

Example validation binding:

<TextBox x:Name="TBNumItems" Margin="2,2,2,2" MinWidth="40" HorizontalAlignment="Left" Validation.ErrorTemplate="{StaticResource errorTemplate}">
    <TextBox.Text>
        <Binding x:Name="NumItemsBinding" Path="NumItems" NotifyOnSourceUpdated="True" UpdateSourceTrigger="PropertyChanged">
            <Binding.ValidationRules>
                <cal:UIntValidationRule x:Name="NumItemsValidationRule" MinValue="1" MaxValue="99999" IsEnabled="False"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

Example code behind for validation:

/// <summary>
/// Clears all validation errors
/// </summary>
void ClearAllValidationErrors()
{
    Validation.ClearInvalid(TBNumItems.GetBindingExpression(TextBox.TextProperty));
}


/// <summary>
///  Revalidates everything
/// </summary>
void RevalidateAll()
{
    ClearAllValidationErrors();

    TBNumItems.GetBindingExpression(TextBox.TextProperty).UpdateSource();
}