NullableBoolExtension.md

title	author	description	keywords
NullableBoolExtension	michael-hawker	The NullableBoolExtension type allows developers to specify default values in XAML for nullable bool dependency properties.	windows 10, uwp, uwp community toolkit, uwp toolkit, nullable bool, dependency property, markup extension, XAML, markup

NullableBoolExtension

The NullableBoolExtension type provides the ability to set nullable bool dependency properties in XAML markup. These types of properties can normally be bound to, but can't be explicitly set to a specific value. This extension provides that capability.

Platform APIs: NullableBoolExtension

Here is an example of how this extension could be used when binding to a DependencyProperty:

<Page.Resources
    xmlns:ui="using:Microsoft.Toolkit.Uwp.UI"
    xmlns:helpers="using:MyApp.Helpers">
    <helpers:ObjectWithNullableBoolProperty
        x:Key="OurObject"
        NullableBool="{ui:NullableBool Value=True}"/>
</Page.Resources>

With the following backend object to use as binding source:

namespace MyApp.Helpers
{
    public class ObjectWithNullableBoolProperty : DependencyObject
    {
        // Using a DependencyProperty as the backing store for NullableBool. 
        // This enables animation, styling, binding, etc...
        public static readonly DependencyProperty NullableBoolProperty = DependencyProperty.Register(
            nameof(NullableBool),
            typeof(bool?),
            typeof(ObjectWithNullableBoolProperty),
            new PropertyMetadata(null));

        public bool? NullableBool
        {
            get => (bool?)GetValue(NullableBoolProperty);
            set => SetValue(NullableBoolProperty, value);
        }
    }
}

Examples

You can find more examples in the unit tests.