Enterprise Development Using Visual Basic 6.0 Autumn 2002 Tirgul # 7

1. Enterprise Development Using Visual Basic 6.0 Autumn 2002Tirgul #7 ‘Tirgul’ # 7

2. Objectives • Brief on COM • COM and Classes • Creating Objects – ActiveX Dll • Registering an Object • Version Compatibility issues ‘Tirgul’ # 7

3. Abstract • In the world of the enterprise, employers want that something more then just Forms and Controls • That something is called COM • It's a way of organizing your code so it can be used over and over again. • It's a method of helping create a bug-free development environment. • Just after making your life a little harder, makes it lot easier. ‘Tirgul’ # 7

4. What is COM? • you're already a COM programmer! • Every time you set the Text property of a Text Box, you're using COM. • COM is a method of communication ‘Tirgul’ # 7

5. COM is a method of communication • Imagine a television remote control • You press button one and the television tunes into Channel 1, 2… • You press the power button and the television turns itself off. • You just press the button and it jumps into action. ‘Tirgul’ # 7

6. COM is a method of communication • That’s applies to the world of programming. • You don't really know what happens when you change the Text property of your Text Box. • Under the covers, it's probably making two-dozen API calls – but to the end user, it just displays a certain piece of text in the box. ‘Tirgul’ # 7

7. COM is a way of reusing code • You can use Com Object again and again anywhere. • A COM widget could be accessed from any program at any time. (Visual Basic, Excel C++ Program) • So COM is all about creating 'widgets' that can be reused. ‘Tirgul’ # 7

8. COM is based around real-life objects • After COM have been made, it’s easy to use. • Add a customer • Instead of adding lots of data access code, validation algorithms, and weighty database DLLs to your application – wouldn't it be easier to run something like Customer.Add ‘Tirgul’ # 7

9. Classes -> COM • All of our work will be surrounding the creation of a class – which could later be turned into a real life COM object ‘Tirgul’ # 7

10. Classes check list  • Variables • Properties (Let/Get) (hopefully).. • Subs, Functions, Parameters • Collection • What else? • Enumeration • Events – Not in the scope    ‘Tirgul’ # 7

11. create a real-life COM object • ActiveX DLL– A .DLL program that contains classes. • ActiveX EXE – A .EXE program that contains classes. • ActiveX Control – A project that allows you to create controls in your toolbox. • ActiveX Document EXE – A program that runs on a Web page, in .EXE format. • ActiveX Document DLL – As above, but .DLL format. ‘Tirgul’ # 7

12. My first object! • We have discussed objects as controls in VB (Textbox, ComboBox) - you should be remembering these by now!) • When you make a control, it has a user interface (that means you can visually see something on the screen, such as the textbox itself • Another kind of object is one that doesn't have a user interface, and we call this a DLL (or Dynamic Link Library if you want to impress your friends). ‘Tirgul’ # 7

13. ActiveX Dll • Click File, New Project and select ActiveX DLL: • make sure that the Instancing property is set to 5 –MultiUse, • Allows us to compile the DLL and expose the class module to other programs (such as the object browser. ‘Tirgul’ # 7

14. Build the DLL • Save the project, and a click File, Make Project1.DLL. • You've just complied your first Dll object! ‘Tirgul’ # 7

15. Testing.. • Add another project - File, Add Project, Standard EXE. • Because a DLL is not a control, we need to make a reference to it (because we are not loading any kind of user interface) ‘Tirgul’ # 7

16. Testing.. • Click File, References and scroll down and select Project1: ‘Tirgul’ # 7

17. Browsing the Object • press F2 to load up the object browser and select Projec1 from the combo box. • Check the Methods.. ‘Tirgul’ # 7

18. Explanation • An ActiveX DLL's code is executed within the main program's address space. • It behaves as if the class was created within the main program's code. • Because the code lies inside the program's address space, calling methods is very fast. ‘Tirgul’ # 7

19. Registering a component • when you come to distribute your DLL to another machine and it doesn't work.. • Each DLL (or component) on your machine has to be registered (including controls). Once registered, an entry in to the registry is made. ‘Tirgul’ # 7

20. Using Regsvr32 Tool • Microsoft tool for registring DLL’s and OCX’s • Simply Drag the Object into the TextBox ‘Tirgul’ # 7

21. Main sub • In the module you can add a main sub: Sub main ‘Add code that will run when the ‘component is created EndSub ‘Tirgul’ # 7

22. Compatibility • Problem: • compile the ActiveX DLL, • then compiled a test program that used our DLL. • Then we recompiled our DLL – something you usually do after you make changes. • Suddenly, our test program no longer worked! ‘Tirgul’ # 7

23. Compatibility • Open up your project • Click 'Project Properties' • Click the 'Component' tab ‘Tirgul’ # 7

24. Version Compatibility • No Compatibility – When compiled, your COM component gets assigned a new 'signature'. Programs looking for older 'signatures' (the previous version of the DLL) – simply flop • Project Compatibility – When compiled, your COM component is assigned a new signature – and still, any using-applications still flop. The only change here is that 'big' differences between your current project and a previous DLL project are highlighted as you compile. • Binary Compatibility – When compiled, your application attempts to keep the signature of a previously compiled DLL, thus ensuring any applications using it don't magically turn into the Blue Screen of Death. However if the differences between your previously compiled DLL and your to-be-compiled DLL are too great, a new signature must be assigned ‘Tirgul’ # 7

25. ActiveX DLL Creation Summary When you create a new ActiveX DLL, the steps you’ll generally follow are these: • Determine the features your component will provide. • Determine what objects are required to divide the functionality of the component in a logical fashion ‘Tirgul’ # 7

26. ActiveX DLL Creation Summary • Design any forms your component will display. • Design the interface — that is, the properties, methods, and events — for each class provided by your component. • Create a project group consisting of your component project and a test project. ‘Tirgul’ # 7

27. ActiveX DLL Creation Summary • Implement the forms required by your component • Implement the interface of each class. • As you add each interface element or feature, add features to your test project to exercise the new functionality. • Compile your DLL and test it with all potential target applications. ‘Tirgul’ # 7