WPF: How to bind to a nested property?

Question

I can bind to a property, but not a property within another property. Why not? e.g.

Answer 1

Do both the ParentProperty and your class implement INotifyPropertyChanged?

    public class ParentProperty : INotifyPropertyChanged
    {
        private string m_ChildProperty;

        public string ChildProperty
        {
            get
            {
                return this.m_ChildProperty;
            }

            set
            {
                if (value != this.m_ChildProperty)
                {
                    this.m_ChildProperty = value;
                    NotifyPropertyChanged("ChildProperty");
                }
            }
        }

        #region INotifyPropertyChanged Members

        #endregion
    }

    public partial class TestClass : INotifyPropertyChanged
    {
        private ParentProperty m_ParentProperty;

        public ParentProperty ParentProperty
        {
            get
            {
                return this.m_ParentProperty;
            }

            set
            {
                if (value != this.m_ParentProperty)
                {
                    this.m_ParentProperty = value;
                    NotifyPropertyChanged("ParentProperty");
                }
            }
        }
}
    public TestClass()

    {
        InitializeComponent();
        DataContext = this;
        ParentProperty = new ParentProperty();
        ParentProperty.ChildProperty = new ChildProperty();

        #region INotifyPropertyChanged Members
        #endregion
    }