Databinding to individual properties of the main Dataobject

This is my ViewModel Code: vb:

Public Property Doctor() As Doctor
        Get
            Return _objDoctor
        End Get
        Set(ByVal Value As Doctor)
            _objDoctor = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property AddDate() As Nullable(Of DateTime)
        Get
            Return _objDoctor.AddDate
        End Get
        Set(ByVal Value As Nullable(Of DateTime))
            _objDoctor.AddDate = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property AddUserID() As String
        Get
            Return _objDoctor.AddUserID
        End Get
        Set(ByVal Value As String)
            _objDoctor.AddUserID = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property ChangeDate() As Nullable(Of DateTime)
        Get
            Return _objDoctor.ChangeDate
        End Get
        Set(ByVal Value As Nullable(Of DateTime))
            _objDoctor.ChangeDate = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property ChangeUserID() As String
        Get
            Return _objDoctor.ChangeUserID
        End Get
        Set(ByVal Value As String)
            _objDoctor.ChangeUserID = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property CollaboratingPhysicianID() As Nullable(Of Int64)
        Get
            Return _objDoctor.CollaboratingPhysicianID
        End Get
        Set(ByVal Value As Nullable(Of Int64))
            _objDoctor.CollaboratingPhysicianID = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property CredentialsID() As Int64
        Get
            Return _objDoctor.CredentialsID
        End Get
        Set(ByVal Value As Int64)
            _objDoctor.CredentialsID = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property DisplayName() As String
        Get
            Return _objDoctor.DisplayName
        End Get
        Set(ByVal Value As String)
            _objDoctor.DisplayName = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property DoctorSpecialtyID() As Int64
        Get
            Return _objDoctor.DoctorSpecialtyID
        End Get
        Set(ByVa开发者_C百科l Value As Int64)
            _objDoctor.DoctorSpecialtyID = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property FirstName() As String
        Get
            Return _objDoctor.FirstName
        End Get
        Set(ByVal Value As String)
            _objDoctor.FirstName = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property ID() As Int64
        Get
            Return _objDoctor.ID
        End Get
        Set(ByVal Value As Int64)
            _objDoctor.ID = Value
            OnPropertyChanged("Doctor")
        End Set
    End Property

    Public Property LastName() As String
        Get
            Return _objDoctor.LastName
        End Get
        Set(ByVal Value As String)
            _objDoctor.LastName = Value
            OnPropertyChanged("LastName")
        End Set
    End Property

Here is on example of XAML that I could use:

<StackPanel>
        <TextBox Text="{Binding LastName}" />
        <TextBox Text="{Binding Doctor.LastName}" />
    </StackPanel>

I would really prefer to bind to my data as the first textbox is so that I can do validation on changes. (if there is a way to do validation with the second way someone please let me know)

The problem is this:

If I load the doctor in the new constructor of the viewmodel as such:

Public Sub New()
    If IsInDesignMode Then
    Else
        CreateEventSubscriptions()
    End If
    Me.Doctor = DoctorService.GetDoctor(4839)

End Sub

The Databinding works correctly the first time. But if I try to change the associated doctor with an Event, only the doctor.lastname binding works.

    Private Sub onEdit(ByVal d As Doctor)
        Me.Doctor = DoctorService.GetDoctor(d)


    End Sub

I know I dont need to load a doctor from my service because I am actually passing the doctor...I was trying to see if there was something magical about using a service to fill the propery.

I got the code for my viewmodel properties using Karl Shifflet's XAML PowerToys. Knowing that Karl knows what he is doing I am not sure why I cant get this to work....hopefully it is something silly I am missing.

I believe if you change the doctor during an event, you should also call:

OnPropertyChanged("LastName")

Otherwise I don't think the binding code has any way of knowing the LastName property has been updated.