VBA collection: list of keys

问题:

After I add some values to the VBA collection, is there any way to retain the list of all keys?

For example

Dim coll as new  Collection Dim str1, str2, str3 str1="first string" str2="second string" str3="third string" coll.add str1, "first key" coll.add str2, "second key" coll.add str3, "third key" 

I know how to retain the list of strings:

first string second string third string 

Once again: is there any way to retain the keys?

first key second key third key 

Note: I'm using VBA through AutoCAD 2007

回答1:

I don't thinks that possible with a vanilla collection without storing the key values in an independent array. The easiest alternative to do this is to add a reference to the Microsoft Scripting Runtime & use a more capable Dictionary instead;

Dim coll As New Dictionary ... Dim K As Variant For Each K In coll.Keys     debug.print "Key: " & K , "Value: " & coll.Item(K) Next 

回答2:

If you intend to use the default VB6 Collection, then the easiest you can do is:

col1.add array("first key", "first string"), "first key" col1.add array("second key", "second string"), "second key" col1.add array("third key", "third string"), "third key" 

Then you can list all values:

Dim i As Variant  For Each i In col1   Debug.Print i(1) Next 

Or all keys:

Dim i As Variant  For Each i In col1   Debug.Print i(0) Next 

回答3:

An alternative solution is to store the keys in a separate Collection:

'Initialise these somewhere. Dim Keys As Collection, Values As Collection  'Add types for K and V as necessary. Sub Add(K, V)  Keys.Add K Values.Add V, K End Sub 

You can maintain a separate sort order for the keys and the values, which can be useful sometimes.

回答4:

You can create a small class to hold the key and value, and then store objects of that class in the collection.

Class KeyValue:

Public key As String Public value As String Public Sub Init(k As String, v As String)     key = k     value = v End Sub 

Then to use it:

Public Sub Test()     Dim col As Collection, kv As KeyValue     Set col = New Collection     Store col, "first key", "first string"     Store col, "second key", "second string"     Store col, "third key", "third string"     For Each kv In col         Debug.Print kv.key, kv.value     Next kv End Sub  Private Sub Store(col As Collection, k As String, v As String)     If (Contains(col, k)) Then         Set kv = col(k)         kv.value = v     Else         Set kv = New KeyValue         kv.Init k, v         col.Add kv, k     End If End Sub  Private Function Contains(col As Collection, key As String) As Boolean     On Error GoTo NotFound     Dim itm As Object     Set itm = col(key)     Contains = True MyExit:     Exit Function NotFound:     Contains = False     Resume MyExit End Function 

This is of course similar to the Dictionary suggestion, except without any external dependencies. The class can be made more complex as needed if you want to store more information.

回答5:

the trouble is that for large datasets, collections perform way better than any dictionary...

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