formulas in WPF bindings

Question

I have a combobox, and I want it to be enabled when checkbox is not checked. How do I write it? I tried following, but it seems that WPF doesn't recognise this syntax:

<ComboBox IsEnabled={Binding Path=!CheckBoxIsChecked, Mode=OneWay}/>
<CheckBox IsChecked={Binding Path=CheckBoxIsChecked}/>

I believe more generic approach would be introducing InverseBooleanConverter ([see here](http://stackoverflow.com/a/1039681/485076)) and use it where you need instead of copy-paste trigger across multiple Views — sll, Jan 27 '12 at 13:53
possible duplicate of [How to bind inverse boolean properties in WPF?](http://stackoverflow.com/questions/1039636/how-to-bind-inverse-boolean-properties-in-wpf) — sll, Jan 27 '12 at 13:53

score 1 · Answer 1 · answered Jan 27 '12 at 13:04

1

You will have to write a converter, i.e. a class that implements the IValueConverter interface. The converter will then be assigned to the Converter property of your binding:

<ComboBox IsEnabled="{Binding Path=CheckBoxIsChecked, Mode=OneWay, Converter={StaticResource MyConverter}}"/>

answered Jan 27 '12 at 13:04

Clemens

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It is easier to write a property CheckBoxIsNotChecked { get { return !CheckBoxIsChecked; } } – Bogdan Verbenets Jan 27 '12 at 13:23
1

Yes, but what if you bind to an object that you don't write yourself, i.e. where you have no control over the set of properties? – Clemens Jan 27 '12 at 13:25

Youp Bernoulli · Answer 2 · 2012-01-27T18:23:14.803

1

You should use so-called converters to do these kind of things.

{Binding ElementName=CheckBox, Path=IsChecked, Converter=BoolToVisibilityConverter}

BoolToVisibilityConverter is a standard WPF converter. You can also easily write a OppositeBoolToVisibilityConverter. Many examples around on the net.

edited Jan 27 '12 at 18:23

answered Jan 27 '12 at 13:04

Youp Bernoulli

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Maheep · Answer 3 · 2012-01-27T13:11:20.130

You will have to use convertor to achieve this.

public class BooleanNegationConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ConvertValue(value);
    }
    private bool ConvertValue(object value)
    {
        bool boolValue;
        if(!Boolean.TryParse(value.ToString(), out boolValue))
        {
            throw new ArgumentException("Value that was being converted was not a Boolean", "value");
        }
        return !boolValue;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ConvertValue(value);
    }
}

Then use it like this:

<ComboBox IsEnabled="{Binding Path=CheckBoxIsChecked, 
                              Mode=OneWay, 
                              Converter={StaticResource BooleanNegationConverterKey}}"/>

Remember you have to declare this static resource in xaml resources. Like this:

<UserControl.Resources>
    <ResourceDictionary>
        <BooleanNegationConverter x:Key="BooleanNegationConverterKey" />
    </ResourceDictionary>
</UserControl.Resources>

score -1 · Accepted Answer · answered Jan 27 '12 at 13:18

A trigger should work just as well for this:

   <CheckBox IsChecked="{Binding Path=CheckBoxIsChecked}" />
    <ComboBox Grid.Row="1" ItemsSource="{Binding Path=ComboItems}" SelectedItem="{Binding Path=SelectedItem, Mode=TwoWay}">
        <ComboBox.Style>
            <Style TargetType="ComboBox">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=CheckBoxIsChecked}" Value="False" >
                        <Setter Property="IsEnabled" Value="True"/>
                    </DataTrigger>
                    <DataTrigger Binding="{Binding Path=CheckBoxIsChecked}" Value="True" >
                        <Setter Property="IsEnabled" Value="False"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </ComboBox.Style>
    </ComboBox>

Wouldn't prefer this solution as sll already mentioned. It's a lot more code and less maintainable over multiple editors in multiple places in the application. — Youp Bernoulli, Jan 27 '12 at 18:25

formulas in WPF bindings

4 Answers4