[英]Check for Null Value in VB.NET
我有一个在AD中搜索属性(extensionAttribute3)的函数。 如果属性具有值,则可以正常工作,但是如果未设置属性,则会出现“对象引用未设置为对象实例”的错误。 这总是会出错:
CurrentPIN = dirResult.GetDirectoryEntry.Properties("extensionAttribute3").Value.ToString
我尝试使用“ If IsNothing”和“ IsNot Nothing”来检查dirResult和CurrentPIN上的NULL值,但仍然出错。 如何成功检查NULL值?
检查dirResult是否为NULL:
Private Function GetUserProperties()
Dim ADName As String = GetLogonName()
Dim CurrentPIN As String = Nothing
Dim dirEntry As DirectoryEntry = GetDirectoryEntry()
Dim dirSearcher As DirectorySearcher = New DirectorySearcher(dirEntry)
dirSearcher.Filter = ("(samAccountName=" & ADName & ")")
dirSearcher.PropertiesToLoad.Add("extensionAttribute3")
dirSearcher.SearchScope = SearchScope.Subtree
Dim dirResult As SearchResult = dirSearcher.FindOne()
If IsNothing(dirResult) Then
Return "<not set>"
Else
CurrentPIN = dirResult.GetDirectoryEntry.Properties("extensionAttribute3").Value.ToString
Return CurrentPIN
End If
End Function
检查CurrentPIN是否为NULL:
Private Function GetUserProperties()
Dim ADName As String = GetLogonName()
Dim CurrentPIN As String = Nothing
Dim dirEntry As DirectoryEntry = GetDirectoryEntry()
Dim dirSearcher As DirectorySearcher = New DirectorySearcher(dirEntry)
dirSearcher.Filter = ("(samAccountName=" & ADName & ")")
dirSearcher.PropertiesToLoad.Add("extensionAttribute3")
dirSearcher.SearchScope = SearchScope.Subtree
Dim dirResult As SearchResult = dirSearcher.FindOne()
CurrentPIN = dirResult.GetDirectoryEntry.Properties("extensionAttribute3").Value.ToString
If IsNothing(CurrentPIN) Then
Return False
Else
Return CurrentPIN
End If
End Function
您应该在Properties(“ extensionAttribute3”)中检查NULL:
If dirResult Is Nothing OrElse dirResult.GetDirectoryEntry.Properties("extensionAttribute3") Is Nothing Then
Return "<not set>"
Else
CurrentPIN = dirResult.GetDirectoryEntry.Properties("extensionAttribute3").Value.ToString
Return CurrentPIN
End If
说明:
Is Nothing
是IMO检查空值一个干净的方式,并且据我所知,还可以节省您的堆栈水平。
如果extensionAttribute3没有值,则说明存在异常,因为
CurrentPIN = dirResult.GetDirectoryEntry.Properties("extensionAttribute3").Value.ToString
被翻译成
CurrentPIN = <NULL>.Value.ToString
在dirResult上检查NULL只是为了防止将来可能发生异常。
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