WPF: TextBox Text is not updating

Question

I have a user control that i am using inside a DataTemplate, this UserControl contains a TextBox which is binded with Value property(declared as a DependencyProperty) of my UserControl. In data template I bind this Value property with my actual property say Name (also a DependencyProperty). It works properly, I assign a value to Name property while loading and my TextBox displays it, i change the value from TextBox and it updates my Name property also. Now the problem comes while I add a PropertyChangedEventHandler in the dependency property, I check for the value if it is valid, do nothing if valid and assign old value if not valid. In case of value not valid, when I assign it that old value, property updates but it is not displaying updated value in my TextBox of UserControl. Can anyone tell me why?

XAML of my UserControl:

<UserControl x:Name="usercontrol">
   <StackPanel>
      <TextBlock ......./>
      <TextBox Binding={Binding ElementName=usercontrol, Path=Value, Mode=TwoWay}/>
   </StackPanel>
</UserControl>

In code behind Value is a DependencyProperty

I am using this in my DataTemplate:

<HierarchicalDataTemplate DataType="{x:Type myLib:myClass}" ItemsSource="{Binding Children}">
    <Expander Header="{Binding}">
        <WrapPanel>
            <edproperty:TextPropertyEditor Caption="Name" Value="{Binding Name, Mode=TwoWay}"/>
            <edproperty:TextPropertyEditor .................../>
            <edproperty:TextPropertyEditor .................../>
            <edproperty:TextPropertyEditor ...................../>
        </WrapPanel>
    </Expander>
</HierarchicalDataTemplate>

This template I am using in a TreeView. Inside TreeView I enter value in the TextBox which updates the Value property of my UserControl, that in turn updates Name property of myClass I am assigning a PropertyChangedCallback to my Name Property in myClass, performing some validation and reassigning the OldValue if the validation fails. It in turn updates Value property also, but i am still seeing that the TextBox has the same value that i entered earlier not the updated one.

public string Name
    {
        get
        {
            return (string)GetValue(NameProperty);
        }
        set
        {
            SetValue(NameProperty, value);
        }
    }

    // Using a DependencyProperty as the backing store for Name.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty NameProperty =
        DependencyProperty.Register("Name", typeof(string), typeof(myClass), new UIPropertyMetadata(null, OnNameChanged));

    protected static void OnNameChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
    {
        if(checkRequired && !IsValid(e.NewValue.ToString()))
        {
            checkRequired=false;
            (sender as myClass).Name = args.OldValue.ToString();
        }
    }

    private static bool IsValid(string name)
    {
         .............some logic here
    }

Answer 1

After days of looking around and a lot of search i found the solution of my problem

After all validation done and assigning old value and updating the dependecy property, i need to cal UpdateTarget() method, to Update the value in my TextBox.

This is what explains the solution better

http://social.msdn.microsoft.com/forums/en-US/wpf/thread/c404360c-8e31-4a85-9762-0324ed8812ef/