Binding to runtime object instance

I'm going round in circles here. I've kind of got the hang of XmlDataProvider bindings but the file I'm using seems too large to bind dynamically (50Mb doesn't work; 2Mb works). So instead I have the data loaded into classes using code generated from the XSD.

However, I can't get binding to CLR objects to work, due to my lack of knowledge. I'm using Visual Studio 2008 Pro, C# and .Net 3.5.

Here's the XAML file:

<Window x:Class="WpfObjectText.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfObjectText"
    Title="Window1" Height="300" Width="300">
    <Grid>
        <Grid.Resources>
            <ObjectDataProvider x:Key="simpleBinding" ObjectType="{x:Type local:ExampleClass}"/>
        </Grid.Resources>
        <StackPanel>
            <TextBox Name="textBox1" Text="{Binding Path=simpleBinding}" />
        </StackPanel>
    </Grid>
</Window>

And the code behind:

using System;
usin开发者_StackOverflow中文版g System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfObjectText
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public ExampleClass TestInstance = new ExampleClass("Hello, world!");

        public Window1()
        {
            InitializeComponent();
        }
    }

    public class ExampleClass
    {
        public string TestString { get; set; }

        public ExampleClass(string initialText)
        {
            TestString = initialText;
        }
    }

}

I've deliberately kept it simple so I can take baby steps. All I want to do here is populate the textbox from an instance of ExampleClass, and have the TestString field updated if the textbox changes (ie bidirectional). I know I can set MethodName in the binding which works to a certain extent in ListBoxes but that doesn't seem to imply bidirectional to me. Coming from a Delphi7 Win32 programmer, this is alien territory for me!

Assistance appreciated.

These are the necessary changes:

<TextBox Name="textBox1" Text="{Binding Path=TestString}" />

and then in the constructor:

DataContext = TestInstance;

If my understanding of the question is correct, you don't need Grid.Resources section at all.