Я пытаюсь получить базовый уровень паттерна MVVM, и меня ударили по ICommand CanExecute. У меня есть привязка XAML следующим образом:

Команды:

Public Class DeleteCommand
Implements ICommand

Private method As Object
Private methodname As String

Public Sub New(ByVal Controlname As String, ByVal mee As Object)
    methodname = Controlname
    method = mee
End Sub

Public Function CanExecute(parameter As Object) As Boolean Implements ICommand.CanExecute
    Select Case methodname
        Case "Address"
            Return TryCast(method, ModelView.Contacts.ContactMV).CanDeleteAddress()
        Case "Numbers"
            Return TryCast(method, ModelView.Contacts.ContactMV).CanDeleteNumbers
        Case Else : Return False
    End Select
End Function

Public Event CanExecuteChanged(sender As Object, e As EventArgs) Implements ICommand.CanExecuteChanged

Public Sub Execute(parameter As Object) Implements ICommand.Execute
    Select Case methodname
        Case "Address"
            TryCast(method, ModelView.Contacts.ContactMV).DeleteAddress()
        Case "Numbers"
            TryCast(method, ModelView.Contacts.ContactMV).DeleteNumbers()
        Case Else

    End Select
End Sub
End Class

Мой ModelView:

Public Class ContactMV

Property Contact As Model.Contacts.ContactMod
Property AddAddressCommand As New Commands.AddCommand("Address", Me)
Property DeleteAddressCommand As New Commands.DeleteCommand("Address", Me)
Property SelectedAddress As Model.Contacts.AddressModel
Public Sub AddAddress()
    If Contact.Addresses.Count = 0 Then
        Contact.Addresses.Add(New Model.Contacts.AddressModel(Contact.Primary.ID, True))
    Else
        Contact.Addresses.Add(New Model.Contacts.AddressModel(Contact.Primary.ID, False))
    End If

End Sub
Public Sub DeleteAddress()
    If IsNothing(SelectedAddress) = False Then
        Try
            Contact.Addresses.Remove(SelectedAddress)
        Catch ex As Exception
            MsgBox("Address not found")
        End Try
    End If
End Sub
Public Function CanDeleteAddress()
    If IsNothing(SelectedAddress) Then
        Return False
    Else
        Return Contact.Addresses.Contains(SelectedAddress)
    End If
End Function
End Class

Проблема в том, что Canexecuteoted запускается только при запуске, я на самом деле хочу, чтобы кнопка удаления была включена только тогда, когда что-то в списке выбрано, и я хочу, чтобы это было сделано методом привязки MVVM - ICommand. Не могли бы вы объяснить, где я ошибся или пропустил понимание реализации ICommand.

Спасибо.

Обновленный код Relay iCommand, который я использую:

    Public Class RelayCommand
        Implements ICommand
        ''' 
        ''' A command whose sole purpose is to relay its functionality to other objects by invoking delegates. The default return value for the CanExecute method is 'true'.
        ''' 
        ''' 

#Region "Declarations"
        Private ReadOnly _CanExecute As Func(Of Boolean)
        Private ReadOnly _Execute As Action
#End Region

#Region "Constructors"
        Public Sub New(ByVal execute As Action)
            Me.New(execute, Nothing)
        End Sub

        Public Sub New(ByVal execute As Action, ByVal canExecute As Func(Of Boolean))
            If execute Is Nothing Then
                Throw New ArgumentNullException("execute")
            End If
            _Execute = execute
            _CanExecute = canExecute
        End Sub
#End Region

#Region "ICommand"
        Public Custom Event CanExecuteChanged As EventHandler Implements System.Windows.Input.ICommand.CanExecuteChanged

            AddHandler(ByVal value As EventHandler)
                If _CanExecute IsNot Nothing Then
                    AddHandler CommandManager.RequerySuggested, value
                End If
            End AddHandler
            RemoveHandler(ByVal value As EventHandler)

                If _CanExecute IsNot Nothing Then
                    RemoveHandler CommandManager.RequerySuggested, value
                End If
            End RemoveHandler

            RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
                'This is the RaiseEvent block
                'CommandManager.InvalidateRequerySuggested()
            End RaiseEvent
        End Event

        Public Function CanExecute(ByVal parameter As Object) As Boolean Implements System.Windows.Input.ICommand.CanExecute
            If _CanExecute Is Nothing Then
                Return True
            Else
                Return _CanExecute.Invoke
            End If
        End Function

        Public Sub Execute(ByVal parameter As Object) Implements System.Windows.Input.ICommand.Execute
            _Execute.Invoke()
        End Sub
#End Region
    End Class

Большая часть кода является копией, но я поняла работу по комментариям ниже.