Vb.net Visual Basic.Net ListView项

错误名称：对象引用未设置为对象的实例

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这就是它的真实外观：

If ListView2.FocusedItem.ImageIndex = 10 Then

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在本例中，在访问其属性ImageIndex属性之前，请尝试检查ListView2.FocusedItem以确保它不是Null/Nothing。 以下是如何添加检查的示例：

Private Sub ListView2_DoubleClick(sender As Object, e As EventArgs) Handles ListView2.DoubleClick
    If ListView2.FocusedItem.ImageIndex = 0 Or ListView2.FocusedItem.ImageIndex = 1 Or ListView2.FocusedItem.ImageIndex = 2 Then
        If TextBox2.Text.Length = 0 Then
            TextBox2.Text += ListView2.FocusedItem.Text
        Else
            TextBox2.Text += ListView2.FocusedItem.Text & "\"
        End If
        RefreshList()
    End If
    'from here doesn't work
    If Not IsNothing(ListView2.FocusedItem) AndAlso ListView2.FocusedItem.ImageIndex = 10 Then
        If TextBox2.Text.Length < 4 Then
            TextBox2.Text = ""                
        Else
            TextBox2.Text = TextBox2.Text.Substring(0, TextBox2.Text.LastIndexOf("\"))
            TextBox2.Text = TextBox2.Text.Substring(0, TextBox2.Text.LastIndexOf("\") + 1)
            RefreshList()
        End If
    End If
End Sub

Public Sub RefreshList()
    ListView2.Items.Clear()
    Dim item = ListView2.Items.Add("...")
    For cnt As Integer = 1 To ListView2.Columns.Count
        item.SubItems.Add("")
    Next     
End Sub

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AndAlso之后的条件只有在AndAlso之前的条件为True时才会被检查。

但是如果它为false，我如何访问该属性而不给我该错误？如果它为false，则您不需要访问该属性。为什么要费心检查一个不存在的对象的属性呢。请阅读有关错误的参考资料。基本上，表单加载时Listview2已满，我只想添加一个新项目，其中包含文本。。。所以List2iew用目录和文件填充自己，我想保留新的第一项名称。。。这意味着，在这种情况下，“后退”。因此，无论何时调用refresh方法，它都会显示项名称，但它不会执行任何操作，因此它是false。我如何修复它？

Private Sub ListView2_DoubleClick(sender As Object, e As EventArgs) Handles ListView2.DoubleClick
    If ListView2.FocusedItem.ImageIndex = 0 Or ListView2.FocusedItem.ImageIndex = 1 Or ListView2.FocusedItem.ImageIndex = 2 Then
        If TextBox2.Text.Length = 0 Then
            TextBox2.Text += ListView2.FocusedItem.Text
        Else
            TextBox2.Text += ListView2.FocusedItem.Text & "\"
        End If
        RefreshList()
    End If
    'from here doesn't work
    If Not IsNothing(ListView2.FocusedItem) AndAlso ListView2.FocusedItem.ImageIndex = 10 Then
        If TextBox2.Text.Length < 4 Then
            TextBox2.Text = ""                
        Else
            TextBox2.Text = TextBox2.Text.Substring(0, TextBox2.Text.LastIndexOf("\"))
            TextBox2.Text = TextBox2.Text.Substring(0, TextBox2.Text.LastIndexOf("\") + 1)
            RefreshList()
        End If
    End If
End Sub

Public Sub RefreshList()
    ListView2.Items.Clear()
    Dim item = ListView2.Items.Add("...")
    For cnt As Integer = 1 To ListView2.Columns.Count
        item.SubItems.Add("")
    Next     
End Sub

If Not IsNothing(ListView2.FocusedItem) AndAlso ListView2.FocusedItem.ImageIndex = 10 Then