Question

I learn bindings in WPF via book. I have wrote such code:

using System;

namespace WpfBinding {
    enum SomeColors {
        Red,
        Green,
        Blue,
        Gray
    }
}

and

using System;

namespace WpfBinding {
    class TestItem {
        SomeColors color;

        public TestItem(SomeColors color) {
            Color = color;
        }
        internal SomeColors Color {
            get { return color; }
            set { color = value; }
        }
        public override string ToString() {
            return Color.ToString();
        }
    }
}

XAML of my Window:

<Window x:Class="WpfBinding.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <ListBox x:Name="listBox" HorizontalAlignment="Stretch" 
                 VerticalAlignment="Stretch" Margin="5"/>
        <ComboBox x:Name="comboBox" HorizontalAlignment="Stretch" 
                  VerticalAlignment="Top" Margin="5" Grid.Column="1"/>
    </Grid>
</Window>

I have tried create binding through code:

using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfBinding {
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
            // Data for listbox
            TestItem[] items = new TestItem[] {
                new TestItem(SomeColors.Red), 
                new TestItem(SomeColors.Green), 
                new TestItem(SomeColors.Green), 
                new TestItem(SomeColors.Red), 
                new TestItem(SomeColors.Blue), 
                new TestItem(SomeColors.Red), 
            };
            // Create ObservableCollection item
            ObservableCollection<TestItem> collection = new ObservableCollection<TestItem>(items);
            listBox.ItemsSource = collection;// set data for listbox

            comboBox.ItemsSource = Enum.GetValues(typeof(SomeColors)); // Get items from my enum

            // Create bindings
            Binding bind = new Binding();
            bind.Source = listBox;
            bind.Path = new PropertyPath("SelectedItem.Color");
            bind.Mode = BindingMode.TwoWay;
           comboBox.SetBinding(ComboBox.SelectedItemProperty, bind);
        }
    }
}

But my binding ain’t working. Why?

Screen:

Answer 1

Here is the error –

System.Windows.Data Error: 40 : BindingExpression path error: 'Color' property
not found on 'object' ''TestItem' (HashCode=13974362)'.  
BindingExpression:Path=SelectedItem.Color; DataItem='ListBox' (Name='listBox');
target element is 'ComboBox' (Name='comboBox'); target property is 'SelectedItem'
(type 'Object')

You need to make the property Color public instead of internal.

From MSDN here –

The properties you use as binding source properties for a binding must
be public properties of your class. Explicitly defined interface
properties cannot be accessed for binding purposes, nor can protected,
private, internal, or virtual properties that have no base
implementation.