VB。 NET：System.NullReferenceException发生

Question

我又回来了，我在这里找不到解决办法。有人可以帮我一把吗？我遇到了“将对象引用设置为对象实例”的问题。

PS：我在这里读到了一些与这个问题相关的链接，但仍然没有运气。这是链接“What is a NullReferenceException, and how do I fix it?”

它说，我们必须检查并填充变量以确保变量具有值。但在我的情况下，我的变量有一个值，为什么它返回“NullReference”错误？

谢谢大家。

以下是我的代码。 （不是整个模块只是程序）

    Private m_imp As Object ' We delegate the details of horz or vert to this class

    Public Sub addWidget1(ByRef widget As Object, ByRef minExtent As Object)

        m_widget1 = widget
        'UPGRADE_WARNING: Couldn't resolve default property of object widget.ZOrder. Click for more: 'ms-help://MS.VSCC.v90/dv_commoner/local/redirect.htm?keyword="6A50421D-15FE-4896-8A1B-2EC21E9037B2"'
        widget.ZOrder()
        'UPGRADE_WARNING: Couldn't resolve default property of object m_imp.minExtent1. Click for more: 'ms-help://MS.VSCC.v90/dv_commoner/local/redirect.htm?keyword="6A50421D-15FE-4896-8A1B-2EC21E9037B2"'
        'UPGRADE_WARNING: Couldn't resolve default property of object minExtent. Click for more: 'ms-help://MS.VSCC.v90/dv_commoner/local/redirect.htm?keyword="6A50421D-15FE-4896-8A1B-2EC21E9037B2"'
        m_imp.minExtent1 = minExtent ' <---- HERE IS THE ERROR
    End Sub

错误：发生了System.NullReferenceException

PS：代码调用功能的错误。

   Private Sub initGUI(ByRef splitter As clsSplitLayout, ByRef navpane As clsPaneNav, ByRef contentpane As clsPaneContent, ByRef detailpane As clsPaneDetail)

    Dim hsplit As New clsSplitLayout
    With hsplit
        .SplitType = clsSplitLayout.SplitterType.HORIZONTAL_SPLIT
        .createSplitBar("bar1", Me)
        .addWidget1(contentpane, 2000)  '<--- HERE'S HOW I CALL THE FUNCTION THAT HAS ERROR.
        .addWidget2(detailpane, 2000)
    End With

Answer 1

当您正在读取其中包含n值的变量时，会发生System.NullReferenceException。

在您的情况下，定义了m_imp但它没有值。

在访问m_imp之前，m_imp必须具有值。