WPF MultiBinding and IMultiValueConverter makes a boolean operation

Question

I would like to make a boolean OR with a MultiBinding and IMultiValueConverter. Unfortunatly the values passed to the converter are alway unset.

• The first trigger "TriggerStyle" works fine. The button is enable/disable according to "KeyPlugged" Value.

• The multibiding triger "EnableTriggerStyle" does not works. In the class "BoolTestConverter", the values array is well set to 2 objects but

values.Length = 2

values[0]=DependencyProperty.UnsetValue

values[1]=DependencyProperty.UnsetValue

XAML file :

<Window.Resources>
    <local:BoolTestConverter x:Key="BoolTestConverter"></local:BoolTestConverter>
    <Style x:Key="TriggerStyle" TargetType="Button">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=KeyPlugged}" Value="false">
                <Setter Property="Button.IsEnabled" Value="False"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
    <Style x:Key="EnableTriggerStyle" TargetType="Button">
        <Style.Triggers>
            <DataTrigger Value="false">
                <DataTrigger.Binding>
                    <MultiBinding Converter="{StaticResource BoolTestConverter}">
                        <Binding Path="KeyPlugged"/>
                        <Binding Path="KeyOpened"/>
                    </MultiBinding>
                </DataTrigger.Binding>
                <Setter Property="Button.IsEnabled" Value="False"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</Window.Resources>

C# File :

class BoolTestConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        bool result = false;

        if (values.Length > 1)
        {
            if (values[0] == null || values[0] == DependencyProperty.UnsetValue)
                throw new NotImplementedException();

            result = System.Convert.ToBoolean(values[0]);
            for (int i = 1; i < values.Length; i++)
            {
                if (values[i] == null || values[i] == DependencyProperty.UnsetValue)
                    throw new NotImplementedException();

                result |= System.Convert.ToBoolean(values[i]);
            }
        }
        else
            throw new NotImplementedException();

        return result;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Thank you.

Answer 1

Everytime a property/value is set the multibinding will be triggered. The first time it is triggered, none of the values are bound (Unset) . So the converter is triggered multiple times.

You should not throw an exception. Rather return return Binding.DoNothing or else the application will break.