How do I bind child entity detail fields to text boxes? - wpf

Question

My RadGridView is bound to child records via the parent entity's navigation property. Users can edit records in the grid. Now I'd like to also allow editing of child records outside of the grid. After selecting a record in the grid you could edit it using text boxes. I can't seem to find the right binding statement for each text box. My working child grid XAML looks something like this:
<telerik:RadGridView Name="childGrid" ItemsSource="{Binding ChildEntitiesNav, Mode=TwoWay}" IsSynchronizedWithCurrentItem="True" AutoGenerateColumns="False">
<telerik:RadGridView.Columns>
<telerik:GridViewDataColumn DataMemberBinding="{Binding ChildFieldOne}" Header="Child Field One"/>
<telerik:GridViewDataColumn DataMemberBinding="{Binding ChildFieldTwo}" Header="Child Field Two" />
I've added text boxes corresponding to each grid column but I can't get any data to appear. I've tried these text box binding statements:
Text="{Binding Path=ChildEntitiesNav.ChildFieldOne}
and Text="{Binding Path=ChildFieldOne}
I'm using WPF and Entity Framework database first. What is the correct binding statement for editing child detail entities via a parent navigation property?
Thanks in advance.
ANSWER: Andrey's response led me to the solution. I simply needed to bind my text boxes to the grid's SelectedItem (rather than binding to the child entity). I added the grid name as the DataContext to my text box:
<TextBox Name="ChildFieldTextBox" Text="{Binding Path=ChildFieldName, Mode=TwoWay, ValidatesOnExceptions=true, NotifyOnValidationError=true}" DataContext="{Binding ElementName=childGrid, Path=SelectedItem, Mode=TwoWay}" />
These links helped:
Here and here.

Answer 1

Here is an article which may help you. It describes how to bind a control to a property of DataGrid's selected item.
Or you can to add SelectedChildEntityNav property to your ViewModel. The RadGridView declaration will look like this:
<telerik:RadGridView Name="childGrid" IsSynchronizedWithCurrentItem="True" AutoGenerateColumns="False"
ItemsSource="{Binding ChildEntitiesNav, Mode=TwoWay}"
SelectedItem="{Binding SelectedChildEntityNav, Mode=TwoWay}">
After that you're able to bind the textboxes to SelectedChildEntityNav's properties.