Question

From the book WPF 4 Unleashed:

Although the source property can be any .NET property on any .NET
object, the same is not true for the data-binding target. The target
property must be a dependency property. Also note that the source
member must be a real (and public) property, not just a simple field.

However, here’s a counter example to the claim that the source must be a property. This program binds a Label and a ListBox to a normal field of type ObservableCollection<int>.

Xaml:

<Window x:Class="BindingObservableCollectionCountLabel.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">

    <DockPanel>

        <StackPanel>
            <TextBox Name="textBox" Text="10"/>
            <Button Name="add" Click="add_Click" Content="Add"/>
            <Button Name="del" Click="del_Click" Content="Del"/>
            <Label Name="label" Content="{Binding Source={StaticResource ints}, Path=Count}"/>
            <ListBox ItemsSource="{Binding Source={StaticResource ints}}"/>
        </StackPanel>

    </DockPanel>
</Window>

C#:

using System;
using System.Windows;
using System.Collections.ObjectModel;

namespace BindingObservableCollectionCountLabel
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<int> ints;

        public MainWindow()
        {
            Resources.Add("ints", ints = new ObservableCollection<int>());

            InitializeComponent();
        }

        private void add_Click(object sender, RoutedEventArgs e)
        {
            ints.Add(Convert.ToInt32(textBox.Text));
        }

        private void del_Click(object sender, RoutedEventArgs e)
        {
            if (ints.Count > 0) ints.RemoveAt(0);
        }
    }    
}

So what’s the official word on what qualifies as a data binding source? Should we only bind to properties? Or are fields technically allowed as well?

Answer 1

No, this doesn’t bind to the field esplicitly, it binds to the field, by using a static resource:

Binding Source={StaticResource ints //StaticResource !!

You can define a static resource whatever you want (basically) and bind to it. If you want to bind directly to your class, you need to use properties as documentation suggests.