Binding to ICommand with MVVM - wpf

Question

I'm totally new with MVVM and its stuff.
Could you help me to correctly bind the WPF button to ICommand.
I'm binding the button:
<Button Command="{Binding OpenWindow}" >
In the ViewModel:
Public Sub New()
OpenWindow = New RelayCommand(New Action(Of Object)(AddressOf ShowWindow))
End Sub
Private Sub ShowWindow()
Dim win As New SecondWindow()
win.Show()
End Sub
And I have the class RelayCommand as:
Public Class RelayCommand
Implements ICommand
Private ReadOnly _CanExecute As Func(Of Boolean)
Private ReadOnly _Execute As Action
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
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)
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 Class
With the above, I have an exception in the ViewModel constructor part saying "Nested sub does not have a signature that is compatible with delegate 'Delegate Sub Action()'. What am I doing wrong?

Answer 1

Change it to this:
OpenWindow = New RelayCommand(New Action(AddressOf ShowWindow))
The RelayCommand requires an action without parameters. Your method ShowWindow also is a method without parameters. But you declare the action with one parameter of type Object.