CODEWITHSUNDEEP
wpfdata-bindingivalueconverter
Rob Goodwin
Rob Goodwin

Reputation: 2777

Negating a Boolean Property when data binding and applying converter

It is possible within XAML binding markup to negate a Boolean property. Not sure if that is the correct description. For example, I am using one of the built in converters for setting the Visibility of a window border control based on if it is active or not.

<Border BorderBrush="{StaticResource BorderColorBrush}" 
        BorderThickness="1" 
        Visibility="{Binding IsActive, 
                     RelativeSource={RelativeSource FindAncestor, 
                                     AncestorType={x:Type Window}}, 
                     Converter={StaticResource bool2VisibilityConverter}}" />

What I want to the opposite of this, I would like the Visibility to be set to false if the Window is active. This is just an example, but I have run across other situations where it would be nice to apply a ‘!’ to a Boolean property that is being evaluated by a stock converter so I do not have to write a custom one.

Upvotes: 3

Views: 5854

Answers (2)

Clemens
Clemens

Reputation: 128098

An alternative would be to use a DataTrigger instead of a binding converter:

<Border BorderBrush="{StaticResource BorderColorBrush}" 
        BorderThickness="1">
    <Border.Style>
        <Style TargetType="Border">
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsActive,
                                       RelativeSource={RelativeSource FindAncestor,
                                                       AncestorType=Window}}"
                             Value="True">
                    <Setter Property="Visibility" Value="Hidden"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Border.Style>
</Border>

Upvotes: 7

Fede
Fede

Reputation: 44048

Either create a negated property in the ViewModel:

public bool IsNotActive {get { return !IsActive; } }

And notify change accordingly,

-- OR --

use an InverseBoolToVisibilityConverter:

public class InverseBoolToVisibilityConverter: BaseConverterMarkupExtension<bool, Visibility>
    {
        public override Visibility Convert(bool value, Type targetType, object parameter)
        {
            return !value ? Visibility.Visible : parameter != null ? Visibility.Hidden : Visibility.Collapsed;
        }

        public override bool ConvertBack(Visibility value, Type targetType, object parameter)
        {
            return value != Visibility.Visible;
        }
    }

Upvotes: 3

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