VBA:运行时错误“91"? [英] VBA: Run time error '91'?

问题描述

我在这里要做的就是保存对当前活动窗口的引用，但它似乎不起作用.它在最后一行给了我一个运行时错误.

All I'm trying to do here is save a reference to the currently active window, but it doesn't seem to be working. It gives me a run time error on the last line.

Dim SourceWindow As Window, QACheckWindow As Window
SourceWindow = ActiveWindow

我不确定为什么.ActiveWindow 不是应该返回当前活动的窗口吗?如果没有，我如何引用它?

I'm not exactly sure why. Isn't ActiveWindow supposed to return the currently active window? If not, how can I make a reference to it?

上面是我函数的开头，所以在它之前是 Sub FuncName()

The above is right at the beginning of my function, so all there is before it is Sub FuncName()

推荐答案

在 VB 中的对象变量需要指定 Set 关键字.作为对象的对象属性也需要Set.当赋值不使用该关键字时，会引发运行时错误 91未设置对象变量".

In VB object variables require the Set keyword to be assigned. Object properties that are objects also need to be Set. Runtime error 91 "object variable not set" is raised when the assignment doesn't use that keyword.

继承自遗留的Let关键字来分配值，以及Set关键字来分配引用；Let 最终被弃用(尽管仍然需要定义属性)而 Set 仍然存在，保留了 VB6/VBA 赋值语法，如 [Let] variable = value，其中Let"是可选的.

This is inherited from legacy Let keyword to assign values, and Set keyword to assign references; the Let eventually was deprecated (although still needed for defining properties) and the Set remained, leaving the VB6/VBA value assignment syntax like [Let] variable = value, where "Let" is optional.

在声明和赋值中:

Dim SourceWindow As Window, QACheckWindow As Window
'this is like saying "Let SourceWindow = ActiveWindow":
SourceWindow = ActiveWindow

SourceWindow 是一个对象，被分配为一个值 - 这会导致 VBA 尝试 let-coercionem> 通过默认成员调用.如果对象未初始化，则成员调用失败并返回错误 91.如果对象已初始化但没有默认成员，则会引发错误 438.

SourceWindow is an object, assigned as if it were a value - this causes VBA to attempt let-coercion through a default member call. If the object wasn't initialized, the member call fails with error 91. If the object was initialized but doesn't have a default member, error 438 is raised.

因此，在这种情况下，由于隐式成员调用而引发错误 91；.net 等效项将是 NullReferenceException:

So in this case error 91 is being raised because of an implicit member call; the .net equivalent would be a NullReferenceException:

Dim SourceWindow As Window, Dim WindowTitle As String
'"SourceWindow" reference isn't set, the object can't be accessed yet:
WindowTitle = SourceWindow.Caption 

<小时>

我在这里有点过火了，但是遗留的 Let statement 不应该与 Let 混淆子句(在 VB.net 中)，它在 LINQ 查询语法(在 VB.net 中)计算一个值并将其分配给一个新的、查询范围的变量(示例取自MSDN):

---

I'm going to go a bit overboard here, but the legacy Let statement should not be confused with the Let clause (in VB.net) which, in the LINQ query syntax (in VB.net), computes a value and assigns it to a new, query-scoped variable (example taken from MSDN):

From p In products 
Let Discount = p.UnitPrice*0.1 '"Discount" is only available within the query!
Where Discount >= 50
Select p.ProductName, p.UnitPrice, Discount

VB.net 分配 values 和 references，无需指定 Let 或 Set，因为在 .net 中，这种区别是一条更细的线，考虑到一切最终是如何从 System.Object... 包括 System.ValueType 派生的.这就是为什么 Set 关键字也在VB.net，以及为什么用于定义属性的 VB.net 语法放弃了 Let 以支持 Set - 因为无参数默认成员 在 VB.NET 中是非法的，所以这种模棱两可的 let-coercion 不会发生.

VB.net assigns both values and references, without the need to specify a Let or a Set, because in .net this distinction is a much thinner line, given how everything ultimately derives from System.Object... including System.ValueType. That's why the Set keyword was also deprecated in VB.net, and also why the VB.net syntax for defining properties has dropped the Let in favor of Set - because parameterless default members are illegal in VB.NET, so this ambiguous let-coercion doesn't happen.

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