Bind Button.IsEnabled to custom validation with XAML?

I am sorry I didn't know how to title my question any better, you name it if you got a good 1.

I have an entity Contact. this per开发者_如何学Cson has navigation properties: Address, Phones (A collection of Phone).

They all implement a custom interface that exposes a property IsValid.

In the contact edito form I have an OK button, I want its IsEnabled property to be true only if:

Contact.IsValid
Contact.Address.IsValid
Array.TrueForAll(Person.Phones.Cast(Of Phone).ToArray, Function(p) p.IsValid)

I prefer not to use a converter, but to do it Xamly only, anyway, I don't mind to use local code (i.e. reference to a method in the current page that returns a boolean value like System.Web.UI.WebControls.CustomValidator or something like this), but I really don not want a converter unless it's the very only option.

Thru this I was able to solve my question.

I bound the IsEnabled property to a dependency-property I placed in the code-behind that returns if items are valid which I called IsValid:

Sub Window_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
    btnOK.DataContext = Me
End Sub

Private m_IsValid As Boolean
Public Property IsValid() As Boolean
    Get
        Return GetValue(IsValidProperty)
    End Get
    Private Set(ByVal value As Boolean)
        SetValue(IsValidPropertyKey, value)
    End Set
End Property

Private Shared ReadOnly IsValidPropertyKey As DependencyPropertyKey = _
                        DependencyProperty.RegisterReadOnly("IsValid", _
                        GetType(Boolean), GetType(PersonEditor), _
                        New FrameworkPropertyMetadata(False))

Public Shared ReadOnly IsValidProperty As DependencyProperty = _
                       IsValidPropertyKey.DependencyProperty

I set the IsValid property at the OnPropertyChanged event handlers of ALL the items to be validated.

In the Xaml I set the button like this:

<Button Name="btnOk" IsEnabled="{Binding IsValid}"/>