How does the VBUC handle VB6 Collections?

Subject

VB6 Collections Migration

Applies to

Migration; Collection; HashTable; ArrayList;StringCollection; StringDictionary

Inquiry Description

The VBUC can migrate VB6 Collections to the following .NET data types, depending on their usage in the original VB6 code: StringCollection, StringDictionary, ArrayList and HashTable. This is a good alternative to the backward compatibility VB6.Collection class, but may lead to numerous manual changes if the usage of Collections in the VB6 source code is not uniform.

Troubleshooting/solution

VB6 Collections could be indexed with either a string key (HashTable-style) or an integer (ArrayList-style). In .NET, we have HashTables that can be indexed with a key and ArrayLists that can be indexed with integers, but we don't have this "hybrid" class that can have both types of access.

When you migrate, the VBUC can detect the way in which you are accessing Collections in your code and based on that, it infers the appropriate replacement. However, for this inference to work correctly in all cases, the usage of each Collection in VB6 must be very uniform and consistent throughout the code (i.e. you can't mix ArrayList-like and HashTable-like access on the same instance of a Collection). Furthermore, if a VB6 Collection contains only String objects, the VBUC may convert that collection to the .NET StringCollection class (for ArrayList-like access) or to the .NET StringDictionary class (for HashTable-like access).

This is a good alternative to the backward compatibility VB6.Collection class (the default conversion for Collections in the VBUC), but may lead to numerous manual changes if the usage of Collections in the VB6 source code is not uniform.

If the conversion of VB6 Collections is generating numerous compilation errors, it is recommended to disable the "VB6.Collection Special Maps" Code Conversion Rule from the Upgrade Profile configuration window. This is also the default VBUC setting for this option. With this setting turned off, VB6 Collections are converted to the VB6.Collection class, which allows both the "ArrayList-like" and the "HashTable-like" types of access.