Programming: VB6/VBA

[Yoko]

Alright

I'm trying to teach myself Interface Classes and Implementation in VB6/VBA and I cant quite get my head around it.

I'm reading about it in VBA Developers Handbook (By Ken Getz & Mike Gilbert) but its just not clicking in my head.

I've looked at sample code and read up about it but I cant find a simple explanation of it, how it works and the benefits.

So if any of you programmers out there have the answer please can you enlighten me!


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Sheep Shagger

[veeeffarr]

Do you know the basics? If no, start there.

T

[Yoko]

Well I know how to create a class with method, events and properties and how to interact with them etc.

I know that when you implement another class you are including its events, properties & methods in to the current class (though not the code, just the declarations)

Originally I thought that implementation is where you write some code in a class then if you write another class and want to import some of the methods, properties & events into your new class without rewriting the code.

I dont understand the benefits of just importing the declarations rather than the code as well.

The samples I've looked at talk about using callbacks instead of raising events but I dont understand how it works!
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Sheep Shagger

[TheShaggyDA]

I'm learning .NET at the mo, and one analogy of an interface class is to think of it as a car radio; although the radio has a pile of coils, chips, and other discrete components, the interface is the bit you interact with - the volume control, tuning knob and station buttons. It means that you don't have to care what is going on in the background, you just know that when you hit a station button, it'll go to that station.

From a DB perspective, it means that you can write a class the allows you to have fixed features - add, delete, change, lookup, without caring whether it's a flat ASCII file or Oracle database in the background.

This means that you write the interface and only specify what it can do, not how it does it. You then write another class that implements that interface.
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[i:6e3bfc7581]But still I fear and still I dare not laugh at the madman...[/i:6e3bfc7581]

[TheShaggyDA]

[Yoko]

But isnt that what a class does anyway...

You write a class to do x, y and z then another programmer can just create an instance of your class, supply any parameters needed and it will do whatever I programmed it to do. That way he doesnt need to see what method x is doing, only knows that it is doing it...

If another programmer then implemented my class he'd see that it has x, y and z but not what I intended x, y and z to do...
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Sheep Shagger

[TheShaggyDA]

I think if it's a normal class, then you can choose which methods you want to inherit, whereas with an interface class you HAVE to implement all of its methods.
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Current: CB500 Previous: CB100N, CB250RS, XJ900F, GT550, GPZ750R/1000RX, AJS M16, R100RT, Enfield Bullet

[i:6e3bfc7581]But still I fear and still I dare not laugh at the madman...[/i:6e3bfc7581]

[Yoko]

My simple example...

Class 1

[Yoko]

Ah ha!!! The penny has just dropped.

I didnt realise that you are meant to use an interface with more than one class.

Cool so I can write an interface and then two or more classes which have the same functions etc as my interface (or write two classes and a corresponding interface) I can then use either classes via the interface as opposed to instancing each class.
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Sheep Shagger