Question

根据Debugger的说法，我得到了一个名为myCancelled的变量，类型为Newtonsoft.Json.Linq.Jtoken，值为Nothing。我也将它转换为Object，所有这些条件都失败了。我的问题很简单：如何检查它是否为Nothing / Null / False / Empty？

这是我尝试过的。这些条件都没有评估为真：

            If myCancelled Is Nothing Then
                'Doesn't come here
            End If
            If myCancelled = DBNull.Value.ToString Then
                'Doesn't come here
            End If
            If myCancelled = "null" Then
                'Doesn't come here
            End If
            If IsDBNull(myCancelled) Then
                'Doesn't come here
            End If
            If myCancelled Is DBNull.Value Then
                'Doesn't come here
            End If
            If String.IsNullOrEmpty(myCancelled) = True Then
                'Doesn't come here
            End If
            If myCancelled.ToString = "Nothing" Then
                'Runtime error
            End If
            If myCancelled = DBNull.Value Then
                'Runtime error
            End If
            If IsNothing(myCancelled) Then
                'Doesn't come here
            End If

我是VB.net的新手，所以任何指针都会受到赞赏。

修改

这个有效，但它允许误报（当myCancelled有值时，条件为真）

            If Not myCancelled Then
                ' It comes here
            End If

Answer 1

这是有效的。当你习惯了Java，C＃等时，VB很难学习。

If Not myCancelled.Equals("Y") Then
    ' It finally came here
End If

检查Newtonsoft.Json.Linq.JToken是否一无所获

1 个答案: