WPF Data Binding To Dictionaries of Custom Objects

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My application needs to cause the appearance of various UI elements to change in response to real-time updates to the value of a property of a corresponding custom object. Each UI element needs to be associated with its own custom object. Sounds like a classic WPF binding problem, right?

I know that I can bind to an object that is a member of a Dictionary using something like:
Content="{Binding [key1]}"
where the "{Binding [key1]..." syntax causes 'key1' to be used to select the desired Dictionary member. What I cannot seem to make happen is binding to a specific property of that desired object. The following does not work:

Content="{Binding [key1], Path=ValueProperty}"

It causes the following to be written to the Output window at runtime:

System.Windows.Data Error: 39 : BindingExpression path error: '

MIDL

OPCTagValue' property not found on 'object' ''Dictionary`2' (HashCode=30880833)'. BindingExpression:Path=ValueProperty; DataItem='Dictionary`2' (HashCode=30880833); target element is 'Button' (Name='button1'); target property is 'Content' (type 'Object')

BTW, One-Way binding is all that is required here and I will be using a ValueConverter to translate the object's property value to the corresponding UI element property value.

Can someone tell me what I am missing here?

TIA.
Tom

Posted 8-May-11 8:28am

tpwright4423

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Pete O'Hanlon · Accepted Answer · 2011-05-08T10:46:00

If you are trying to bind to a particular dictionary element, then you can use a fairly simple trick. First of all, here's a bit of code-behind that we are going to use to bind to.

C#

using System.Collections.Generic;
using System.Windows;
namespace BindingSampleTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public Dictionary<string, OPC> Tag { get; set; }
        public MainWindow()
        {
            InitializeComponent();
            Tag = new Dictionary<string, OPC>();
            Tag.Add("Test", new OPC { OPCTag = "Hello" });
            Tag.Add("Test2", new OPC { OPCTag = "Hello there" });
            DataContext = Tag;
        }
        public class OPC
        {
            public string OPCTag { get; set; }
        }
    }
}

Now, let's add the XAML bindy-goodness and rejoice at the gooeyness that is WPF data binding.

XML

<Window x:Class="BindingSampleTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="OPC Window" Height="350" Width="525">
    <Grid>
        <TextBlock Text="{Binding [Test].OPCTag}" />
    </Grid>
</Window>

If you look at the Binding, you can see that the trick is just to use the dot property to access it. I hope this helps.