检查 Variant 值“Nothing" [英] Checking for the Variant value "Nothing"
本文介绍了检查 Variant 值“Nothing"的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
这是我去年遇到的事情，所以似乎是记录它的好地方:)
This is something I ran into last year, and SO seems like a good place to document it :)
问:从 Delphi 自动化 Excel (/Word/...) 时，如何检查 Excel 函数是否返回了变体 Nothing(在 VBA 中调用)?
Q: When automating Excel (/Word/...) from Delp how can I check if an Excel function returned the variant Nothing (as it's called in VBA)?
推荐答案
VarIsClear 函数包括类型为 varDispatch 且值为 nil 的情况.它还包括空值和未知"值，以及自定义变体类型.我在我的 Delphi 2005 源代码中看到了它；我不知道它提前多久被收录.
The VarIsClear function includes your situation where the type is varDispatch and the value is nil. It also includes empty and "unknown" values, and custom variant types. I see it in my Delphi 2005 source; I don't know how much earlier it was included.
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