Amazon.com Widgets Even More Changes to HTMLWriter

Even More Changes to HTMLWriter

By Nick at January 09, 2011 05:19
Filed Under: Delphi, Software Development, Unit Testing

Okay, so if you are actually using THTMLWriter, I’m sorry – but I made another pretty major change to it, one that will require you to again make changes to any existing code that you have.  Such are the perils of using pre-1.0 software I suppose.

These changes are made at the suggestion of a number of you fine people, and I’m grateful for your wisdom and for taking the time to critique my work and make such good suggestions. 

Interface Only Access

If you have an interface you want people to use, then you should provide a way for them to use it.  In fact, the really cool thing to do is to make it so that it is the only way to do it.  One iron-clad rule of interfaces is that you should never mix interfaces and instances of the classes that implement them.  The interface is the important thing, not how the interface is implemented. 

An interface is a “promise” of a specific service, and a consumer of an interface shouldn’t care about the implementation details of an interface.  Indeed, that is one of the main advantages of interfaces – that you can “switch out” what you use to actually implement the interface.  If one of you guys things my implementation sucks and want to create a new one, you can simply create a class that implements IHTMLWriter and use that instead without changing any of the code that you have using IHTMLWriter.

So What Did I Do This Time?

Okay, so here’s what I did.

  • I created three standalone functions that return a reference to the IHTMLWriter interface.  They correspond to the three constructors that are included in the THTMLWriterclass.  This is the only way to “get at” the IHTMLWriter interface. 
  • I “hid” the entire THTMLWriterclass in the implementation section of the uHTMLWriter.pas unit.  Now, you can’t even get at the class even if you wanted to.  You must deal exclusively with the interface. 
  • I put the two interfaces I created – IHTMLWriter and ILoadSave -- in their own units.  This way, they aren’t coupled together and can be used separately if desired. 
  • I put all the /// comments in the interface unit instead of on the class. 
  • I had to make changes to the tests to support the new way of grabbing an interface reference.  I made the names of the functions similar enough to the code you current have that it will just be a matter of deleting a few characters.  Of course, all the tests still pass.

What’s Left?

I have a few more things to implement – mostly support for some less common tags that go in specific places inside a <table> tag.  After I do that, I think then I’ll declare THTMLWriter to be an official 1.0 release.

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