vb.net - VB检查结构体的值

Question

我有两种结构，有时其中一种会填充来自用户的数据，有时两种结构都会填充。我需要检查整个结构以查看它是否有数据输入。如果我什至可以检查一个变量以查看它是否不为空或为 null(这就是我在下面所做的)，我也可以。当代码运行时，无论结构是否有数据，btnTurn.Enabled 总是被禁用。这可能是我的 bool 值有问题吗？

结构

 Public Structure StructSurvData
            Friend szTBMNum As String
            Friend dblTBMElev1 As Double
            Friend dblTBMElev2 As Double
            Friend dblTBMElev3 As Double
            Friend dblBACKSIGHT1 As Double
            Friend dblBACKSIGHT2 As Double
            Friend dblBACKSIGHT3 As Double
            Friend dblFORESIGHT1 As Double
            Friend dblFORESIGHT2 As Double
            Friend dblFORESIGHT3 As Double
            Friend szNewMPEDescr As String
            Friend szDataComm As String

        End Structure

        Public Structure StructSurvData2
            Friend szTBMNum2 As String
            Friend dblTBMElev4 As Double
            Friend dblTBMElev5 As Double
            Friend dblTBMElev6 As Double
            Friend dblBACKSIGHT4 As Double
            Friend dblBACKSIGHT5 As Double
            Friend dblBACKSIGHT6 As Double
            Friend dblFORESIGHT4 As Double
            Friend dblFORESIGHT5 As Double
            Friend dblFORESIGHT6 As Double
            Friend szNewMPEDescr2 As String
            Friend szDataComm2 As String
        End Structure

如果/否则

 If structSD2.szTBMNum2 = Nothing Then
                btnTurn.Enabled = False
            ElseIf structSD2.szTBMNum2 <> Nothing Then
                btnTurn.Enabled = True
            End If

Answer 1

您应该始终使用 is nothing而不是 =nothing和 isnot nothing而不是 <> nothing

        If structSD2.szTBMNum2 is Nothing Then
            btnTurn.Enabled = False
        ElseIf structSD2.szTBMNum2 isnot Nothing Then
            btnTurn.Enabled = True
        End If

或者像@zaggler 推荐的那样更好:

        btnTurn.Enabled = structSD2.szTBMNum2 Is Nothing