使用VB.NET IIF我得到的NullReferenceException [英] Using VB.NET IIF I get NullReferenceException

问题描述

我做的一点点调试，所以我想记录的EventArgs值

I am doing a little debugging, and so I want to log the eventArgs value

我有一个简单的线条，基本上不会：

I have a simple line that basically does:

logLine = "e.Value: " + IIf(e.Value Is Nothing, "", e.Value.ToString())

据我所知，IIF函数，如果e.Value为Nothing（空），那么它应该返回空字符串，如果没有它应该返回的值的ToString方式。我，但让一个NullReferenceException。这是没有道理给我。

The way I understand the IIF function, if the e.Value is Nothing (null) then it should return the empty string, if not it should return the .ToString of the value. I am, however getting a NullReferenceException. This doesn't make sense to me.

任何想法的？

推荐答案

IIF 是一个实际功能，所以所有的参数得到评估。该如果的关键字加入到2008年VB.NET提供短路功能，你期待的。

IIf is an actual function, so all arguments get evaluated. The If keyword was added to VB.NET 2008 to provide the short-circuit functionality you're expecting.

尝试

logLine = "e.Value: " + If(e.Value Is Nothing, "", e.Value.ToString())

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