通过使用索引/项目编号的Scripting.Dictionary循环 [英] Looping through a Scripting.Dictionary using index/item number

问题描述

与此问题类似，当使用 Scripting.Dictionary 对象在VBA中，下面的代码的结果是意想不到的。

Similar to this issue, when using a Scripting.Dictionary object in VBA, the outcome of the code below is unexpected.

Option Explicit

Sub test()

    Dim d As Variant
    Dim i As Integer
    Dim s As String
    Set d = CreateObject("Scripting.Dictionary")

    d.Add "a", "a"
    Debug.Print d.Count ' Prints '1' as expected

    For i = 1 To d.Count
        s = d.Item(i)
        Debug.Print s ' Prints ' ' (null) instead of 'a'
    Next i

    Debug.Print d.Count ' Prints '2' instead of '1'

End Sub

相同的结果实现：

For i = 0 To d.Count - 1
    s = d.Item(i)
    Debug.Print s
Next i

观看对象我实际上可以看到在它有两个项目，新添加的关键是 1 ，从 i 添加。如果我将此循环增加到更高的数字，那么字典中的项目数量会增加，每次循环一次。

Watching the object, I can actually see that it has two items, the key for the newly added is 1, as added from i. If I increase this loop to a higher number, then the number of items in the dictionary is increased, once for each loop.

我已经在Office / VBA 2003年，2010年和2013年。都表现出相同的行为，我期望其他版本（2007）也将。

我可以解决这与其他循环方法，但是当我尝试存储对象时，我抓住了我的防守，并且在 s = d.Item（i）上获得了一个对象预期错误 / code>行。

I can work around this with other looping methods, but this caught me off guard when I was trying to store objects and was getting an object expected error on the s = d.Item(i) line.

为了纪录，我知道我可以这样做：

For the record, I know that I can do things like this:

For Each v In d.Keys
    Set o = d.item(v)
Next v

但是我更好奇为什么我似乎无法通过数字迭代项目。

But I'm more curious about why I can't seem to iterate through the items by number.

推荐答案

根据文档的项目属性：

设置或返回Dictionary对象中指定键的项目。

Sets or returns an item for a specified key in a Dictionary object.

在你的情况下，你没有一个项目的密钥是 1 这样做：

In your case, you don't have an item whose key is 1 so doing:

s = d.Item(i)

实际上创建一个新的您的字典中的键/值对，值为空，因为您没有使用可选的 newItem 参数。

actually creates a new key / value pair in your dictionary, and the value is empty because you have not used the optional newItem argument.

该词典还具有 项目方法允许循环遍历索引：

The Dictionary also has the Items method which allows looping over the indices:

a = d.Items
For i = 0 To d.Count - 1
    s = a(i)
Next i

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