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Review
Undo Engine
Issue: 1.3 (December/January 2002)
Author: Daniel Howard
Article Description: No description available.
Article Length (in bytes): 3,394
Starting Page Number: 9
RBD Number: 1304
Resource File(s): None
Related Link(s): None
Known Limitations: None
Full text of article...
When you think of undo (and redo) functionality, what is the first type of application that pops into your head? A text editor, right? Well, as this class illustrates, Undo and Redo are not just for the text editor anymore. You can literally undo or redo anything you want in your application. Someone checks a CheckBox, you can uncheck it; someone switches rows in a PopupMenu, you can switch it back. The list goes on to include almost all interface elements.
Undo Engine is not one of the easiest classes to include in your own application; however, the example file that is included should provide enough help for most users to catch on quickly. Unfortunately, no documentation is included with the package. The example project included shows you how to make your own classes for a CheckBox undo, an EditField undo, and a Color Picker undo. Each works exceptionally well and paves the way for users to find methods of implementing the class for other controls. Due to the lack of documentation, it is not clear whether styled text is or is not supported. However, third party undo classes typically do not support styled text, so even if it is not supported this deficiency would not necessarily be a major weakness.
If you've ever tried to implement an undo function in your application, you know it can be a daunting task. Undo Engine can give you relatively powerful control over undo functionality in your REALbasic project, and in doing so it can knock a rather unpleasant problem off of your "To Do" list.
The class is distributed as open source, so users have access to all aspects of the code and can therefore usually find their own way through the features of the class. Like most undo classes, this class is extremely memory hungry. If you're worried about memory considerations in your application you might look around to see if you can find a more memory-conservative implementation, or simply make sure you limit the number of undos you allow your users. The drawbacks found in this class have basic workarounds and do not seriously affect the usability of the class. In fact, there is no drawback to this class that is not to be expected from an undo class in general. I would recommend this class to anyone who has had trouble implementing their own undo method.
In Brief Product Undo Engine Manufacturer Belle Nuit Montage Price Open Source System Requirements Mac OS 8.1+, Mac OS X 10.1+, REALbasic 4.5+ Contact Info http://www.belle-nuit.com/realbasic/undoengine.html matti-at-belle-nuit.com Pros Free; easy to use; good feature set Cons No documentation; very memory hungry Rating (1.0-5.0): 3.2
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