VB.NET - IIF抛出奇怪的例外
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14-11-2019 - |
题
我有一个奇怪的问题。当我使用一个数组时,IIF正在搞砸。显然,即使它没有被激活,它也在检查我的否则声明。以下是一些代码演示问题:
'works
Dim test As String = "bleh"
If values.Length < 6 Then
test = "200"
Else
test = values(5)
End If
'throws indexoutofrange exception
Dim itemLimit As String = IIf(values.Length < 6, "200", values(5))
. 解决方案
The Iif
operator doesn't implement short circuiting and will evaluate both the true and false case. If you want a short-circuit version then use If
.
Dim itemLimit As String = If(values.Length < 6, "200", values(5))
其他提示
Have a look at this article: http://www.fmsinc.com/free/newtips/net/nettip33.asp
From the article:
Visual Basic, VBA, and Visual Basic .NET support the IIF function as an alternative to the If...Then...Else statement. Although this may seem like a shortcut, IIF functions differently than If...Then...Else.
IIF must evaluate the entire statement when preparing the argument, which can lead to undesirable side effects.
In other words, your If...Then...Else
works because the Else
clause isn't being evaluated if the condition fails. The IIf
, on the other hand, evaluates all the statements, causing the IndexOutOfBounds
exception.