A Null Refrence Exception while working with Properties

Do you see where the problem lies? Code will run from frmFacility and will shift into UserControl:

Public Class frmFacility
Private primaryBaseDay As Date
Private isClassPrimaryView As Boolean = False
Friend WithEvents BookCtrl As ucBookCtrl2
Public Property Primary_BaseDay() As Date
    Get
      Return primaryBaseDay
    End Get
    Set(ByVal value As Date)
      primaryBaseDay = value
    End Set
  End Property

  Public Property IsOnPrimaryView() As Boolean
    Get
      Return isClassPrimaryView
    End Get
    Set(ByVal value As Boolean)
      isClassPrimaryView = value
    End Set
  End Property
Public Sub GotoDay(ByVal theDay As Date)
    Primary_BaseDay = theDay
    IsOnPrimaryView = True
    BookCtrl.GotoDay(theDay)
End Sub
End Class

   Imports frmFacility
Public Class ucBookCtrl2
Public Sub GotoDay(ByVal whichDay As Date, Optional ByVal MainFacilityUsed As String = "")
Dim facilityForm As frmFacility
If facilityForm.IsOnPrimaryView Then
        moDoBooking.m_BaseDay = facilityForm.Primary_BaseDay
        moDoBooking.m_CurrentDay = whichDay
        ShowDay()
        RaiseEvent ChangeOfDay()
End Sub
End Class

At the line If facilityForm.IsOnPrimaryView Then, I get a NullReferenceException. Do you know the reason?

Also, I cannot create a new instance of the facilityForm, since I n开发者_开发技巧eed to work with its singleton, although when I add a new instance of frmFacility, the IsOnPrimaryMode is set to false while it should be set to true in the gotoday sub from frmFacility.

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You didn't set the facilityForm to anything, you simply declared a variable of type frmFacility and called it facilityForm. When you attempt to call facilityForm.IsOnPrimaryView, facilityForm is still null.

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You're not actually working with the facilityForm singleton. You will have to store it somewhere. Maybe a Public Class with a Shared test as New frmFacility.

The Form can not have the IsOnPrimaryView property yet because it is not instanciated. It is practically Nothing

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You need to set IsOnPrimaryView property as shared, otherwise you will get NullReference exception.