Binding Enumerations :: K-State CIS 400 Textbook

Now let’s delve into a more complex data binding examples - binding enumerations. For this discussion, we’ll use a simple enumeration of fruits:

/// <summary>
/// Possible fruits
/// </summary>
public enum Fruit
{
    Apple,
    Orange,
    Peach,
    Pear
}

And add a FavoriteFruit property to our Person class:

private Fruit favoriteFruit;
/// <summary>
/// The person' favorite fruit
/// </summary>
public Fruit FavoriteFruit
{
    get { return favoriteFruit; }
    set
    {
        favoriteFruit = value;
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("FavoriteFruit"));
    }
}

For example, what if we wanted to use a ListView to select an item out of this enumeration? We’d actually need to bind two properties, the ItemSource to get the enumeration values, and the SelectedItem to mark the item being used. To accomplish this binding, we’d need to first make the fruits available for binding by creating a static resource to hold them using an ObjectDataProvider:

<ObjectDataProvider x:Key="fruits" ObjectType="system:Enum" MethodName="GetValues">
    <ObjectDataProvider.MethodParameters>
        <x:Type TypeName="local:Fruit"/>
    </ObjectDataProvider.MethodParameters>
</ObjectDataProvider>

The ObjectDataProvider is an object that can be used as a data source for WPF bindings, and wraps around an object and invokes a method to get the data - in this case the Enum class, and its static method GetValues(), which takes one parameter, the Type of the enum we want to pull the values of (provided as the nested element, <x:Type>).

Also, note that because the Enum class is defined in the System namespace, we need to bring it into the XAML with an xml namespace mapped to it, with the attribute xmlns defined on the UserControl, i.e.: xmlns:system="clr-namespace:System;assembly=mscorlib".

Now we can use the fruits key as part of a data source for a listview: <ListView ItemsSource="{Binding Source={StaticResource fruits}}" SelectedItem="{Binding Path=FavoriteFruit}"/>

Notice that we use the Source property of the Binding class to bind the ItemsSource to the enumeration values exposed in the static resource fruits. Then we bind the SelectedItem to the person’s FavoriteFruit property. The entire control would be:

<UserControl x:Class="DataBindingExample.PersonControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     
             xmlns:local="clr-namespace:DataBindingExample"
             xmlns:system="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="400">
    <UserControl.Resources>
        <ObjectDataProvider x:Key="fruits" MethodName="GetValues" ObjectType="{x:Type system:Enum}">
            <ObjectDataProvider.MethodParameters>
                <x:Type TypeName="local:Fruit"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
    </UserControl.Resources>
    <StackPanel>
        <TextBlock Text="{Binding Path=FullName}"/>
        <Label>First</Label>
        <TextBox Text="{Binding Path=First}"/>
        <Label>Last</Label>
        <TextBox Text="{Binding Path=Last}"/>
        <CheckBox IsChecked="{Binding Path=IsCartoon}">
            Is a Looney Toon
        </CheckBox>
        <ListView ItemsSource="{Binding Source={StaticResource fruits}}" SelectedItem="{Binding Path=FavoriteFruit}"/>
    </StackPanel>
</UserControl>

Binding a ComboBox to an Enum

Binding a <ComboBox> is almost identical to the ListView example; we just swap a ComboBox for a ListView:

<UserControl x:Class="DataBindingExample.PersonControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     
             xmlns:local="clr-namespace:DataBindingExample"
             xmlns:system="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="400">
    <UserControl.Resources>
        <ObjectDataProvider x:Key="fruits" MethodName="GetValues" ObjectType="{x:Type system:Enum}">
            <ObjectDataProvider.MethodParameters>
                <x:Type TypeName="local:Fruit"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
    </UserControl.Resources>
    <StackPanel>
        <TextBlock Text="{Binding Path=FullName}"/>
        <Label>First</Label>
        <TextBox Text="{Binding Path=First}"/>
        <Label>Last</Label>
        <TextBox Text="{Binding Path=Last}"/>
        <CheckBox IsChecked="{Binding Path=IsCartoon}">
            Is a Looney Toon
        </CheckBox>
        <ComboBox ItemsSource="{Binding Source={StaticResource fruits}}" SelectedItem="{Binding Path=FavoriteFruit}"/>
    </StackPanel>
</UserControl>

Binding RadioButtons to an Enum

Binding a <RadioButton> requires a very different approach, as a radio button exposes an IsChecked boolean property that determines if it is checked, much like a <CheckBox>, but we want it bound to an enumeration property. There are a lot of attempts to do this by creating a custom content converter, but ultimately they all have flaws.

Instead, we can restyle a ListView to look like radio buttons, but still provide the same functionality by adding a <Style> that applies to the ListViewItem contents of the ListView:

<Style TargetType="{x:Type ListViewItem}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate>
                <RadioButton Content="{TemplateBinding ContentPresenter.Content}" IsChecked="{Binding Path=IsSelected, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"/>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

This style can be used in conjunction with a ListView declared as we did above:

<UserControl x:Class="DataBindingExample.PersonControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     
             xmlns:local="clr-namespace:DataBindingExample"
             xmlns:system="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="400">
    <UserControl.Resources>
        <ObjectDataProvider x:Key="fruits" MethodName="GetValues" ObjectType="{x:Type system:Enum}">
            <ObjectDataProvider.MethodParameters>
                <x:Type TypeName="local:Fruit"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
        <Style TargetType="{x:Type ListViewItem}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate>
                        <RadioButton Content="{TemplateBinding ContentPresenter.Content}" IsChecked="{Binding Path=IsSelected, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </UserControl.Resources>
    <StackPanel>
        <TextBlock Text="{Binding Path=FullName}"/>
        <Label>First</Label>
        <TextBox Text="{Binding Path=First}"/>
        <Label>Last</Label>
        <TextBox Text="{Binding Path=Last}"/>
        <CheckBox IsChecked="{Binding Path=IsCartoon}">
            Is a Looney Toon
        </CheckBox>
        <ListView ItemsSource="{Binding Source={StaticResource fruits}}" SelectedItem="{Binding Path=FavoriteFruit}"/>
    </StackPanel>
</UserControl>