Question

你看到问题所在吗？代码将从frmFacility运行，并将转换为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

在If facilityForm.IsOnPrimaryView Then行，我得到NullReferenceException。你知道原因吗？

此外，我无法创建facilityForm的新实例，因为我需要使用其单例，但是当我添加frmFacility的新实例时，IsOnPrimaryMode已设置到false，true来自gotoday的{{1}}。{/ 1}}。{/ 1}

Answer 1

您没有将facilityForm设置为任何内容，您只需声明frmFacility类型的变量并将其命名为facilityForm。当您尝试拨打facilityForm.IsOnPrimaryView时，facilityForm仍为null。

Answer 2

您实际上并没有使用facilityForm单例。你必须把它存放在某个地方。也许是Public Class Shared test as New frmFacility。

Form还没有IsOnPrimaryView属性，因为它没有实例化。实际上是Nothing

Answer 3

您需要将IsOnPrimaryView属性设置为shared，否则您将获得NullReference异常。

使用Properties时出现Null Reference Exception

3 个答案: