Delphi 97

Despite critical acclaim, sales of Delphi 2 (reviewed issue 19, p126) were disappointing, particularly in the US. But maybe this was inevitable, given that Delphi, though a US product, is based on British export Pascal, and also given the uncertainties over Borland's future.

Here, however, things are different. Many schools and colleges teach Pascal, so it's often a first language for computer science graduates, making the Delphi marketplace far more active here than in the US. The UK is a smaller market, though, so something had to be done to Delphi - and quickly. With more and more corporate development stressing Web deployment, and with a greater emphasis on ActiveX, Borland realised that Delphi 2 was out on a limb and that Visual Basic 5 was about to saw through the branch.

Enter the new version of Delphi: a 97 edition, no less, and the links to Office are not just in name only. ActiveX/OCX support is now prominent. Recently, Jon Honeyball enthused in his column about the new CCE (Control Creation Edition) of VB 5 (look out for a full review soon), and I spent a couple of months in my own column describing how to create a slider control using CCE. VB 5 was heralded then as the fastest, easiest way to create ActiveX controls. However, two months is a long time in the computer industry. Delphi 97 lets you take an existing control built with the VCL (Delphi's Visual Control Library application framework) and turn it into a re-usable ActiveX control in one step. Borland calls the technology 'One-Step' control development.

Like Visual Basic 5, Delphi 97 has an elaborate New Project box from which you select your desired type of project. If you choose ActiveX Control, you're presented with a list of currently registered VCL controls. Pick one of these and Delphi 97 creates a new project for you, adding all the 'wrapper' code which encapsulates a Delphi component as an ActiveX control. VCL properties, events and methods are made visible through the appropriate interfaces, so that your control ends up with the properties you expect. All you have to do is build the project, and suddenly you've got a brand new OCX control with an autogenerated type library file. You have to rename the resulting DLL (dynamic link library) with the extension 'OCX', but that's not hard.

I experimented with this, converting a few Delphi components into ActiveX components, and then using them inside Visual C++ and VB 4 and 5. A typical OCX file as generated by Delphi 97 is about 200Kb in size, but you can bring this down to about 20Kb by making use of another new Delphi 97 feature: package support.

Notice the different philosophies: VB 5 is all about creating controls from scratch (or from existing components), whereas Delphi 97 is about the conversion of existing VCL components into ActiveX controls. This will boost the VCL control market, as developers realise they can cover both Delphi and ActiveX with one set of source code.

You can also create controls from scratch using Delphi 97 - it just takes more work. In order to support the COM interface, Borland's designers added a new interface key word to the Object Pascal language. You can now describe abstract COM interfaces and then introduce a new object class which implements one or more of those interfaces, thus decoupling the specification of an interface from its implementation.

VB 5 lets you take an existing Visual Basic form and convert it into an ActiveX document which can be deployed inside Internet Explorer - right across the Internet. Hard on the heels of this feature comes ActiveForms, Delphi's equivalent technology, which lets you do the same thing.