Visual Basic Design Patterns VB 6 0 and VB NET

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The trouble is lets say you take a 10, line application and try to convert it. But if someone wants to convert to VB. NOT, it would be better to proceed like this:.

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Step 1. Run a tool that identifies conversion problems in the original code. Fix those problems while still in VB6 and while the app still compiles and works. Step 2. Run the converter. Decide whether to continue on with the converted, broken code, or go back and continue to work on the original code. For example I have a huge. I share it between projects, but each project only uses a small percentage of the declares. Also: it would be nice if you would allow for user-defined conversion patterns.

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Then when something causes the converter to barf, on something that occurs all over the place in the program, I can add something to tell the converter how to handle it, rather than change every instance by hand. I think you have grossly misunderstood the extent to which people have to work around Microsoft BS, so that you have things in VB code like a zillion API calls, memory copies, etc. Well, you have my sympathy.

Disposing Objects

When we talk with people at migration we talk about various approaches and picking the option that works best for you. Each application and company is different and needs to be examined for the best solution. NET in the same application is the best option. This is the course of action most people take. You can leave middleware allow in COM objects and replace the front end. You can replace the middleware and leave the front end allow, the possibilities are pretty open to migrate in steps of months or potentially years if desired.

Visual Basic Design Patterns VB 6 0 and VB NET

For some people the state of the application, age, quality of the original application, in house knowledge of the code, etc… can lead to the recommendation that the best course of action is to rebuild the project from scratch. While the most work, in some cases, this is the best and fastest approach. When this is the case our recommendation is exactly the two steps that you suggest.

Once installed, the add-in can scan your Visual Basic 6. The Code Advisor can also suggest changes and best practices to ease your migration from Visual Basic 6. NET, and enables you to create custom scanning rules to check your Visual Basic 6. This covers many of the points you raise. It raises issues in the VB 6. You can and should fix the problems in the VB 6.

This will migrate your code to VB. We can handle Workbook events in the ThisWorkbook document class module, because the code of ThisWorkbook already includes every member of a Workbook class, even before we write a single line of code in it:. The net effect being that in the ThisWorkbook module we have a Workbook event provider we can pick from the left-hand side code pane drop-down, listing the available events in the right-hand side drop-down — exactly as if there was an implicit WithEvents Workbook private field in any other class module:.

We use the WithEvents keyword to declare an object variable for which we would like to handle events. The keyword is only legal in class modules this includes document class modules and userform modules , and the As clause may only specify a class that exposes public events. Moreover, an auto-instantiated object cannot be declared WithEvents , so As New is also illegal. The Event and WithEvents keywords provide language-level assistance with the otherwise relatively complex wiring-up of callbacks.

In order to use them with interfaces, we can use an adapter pattern with formalized SomethingEvents interfaces — like how the Battleship project demonstrates with the GridViewAdapter and IGridViewEvents classes. Say you have a ListObject on Sheet1 , that would be named Table1 ; you could have a Table1 property that would return this ListObject :. The only problem, is that when the Table1 table is inevitably renamed right?

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Enter On Error Resume Next :. Error handling is promptly explicitly restored with On Error GoTo 0 , and the property will now return Nothing and defer to the caller the decision of what to do with an invalid table:. Assuming the table initially exists on the worksheet, the first call to Me. In the second call to Me. Is that clearly intentional? Did you guess it right? When you see On Error Resume Next at the top of a rather large procedure, comment it out and run the code if possible; see what errors are being silently shoved under the carpet, what code executes in that uncertain error state.

In the above code for example, the error raised here:. Error-handling in VBA can easily get hairy. The best error handling code is no error handling code at all, and by writing our code at a high enough abstraction level, we can achieve exactly that — and leave the gory details in small, specialized, lower-abstraction procedures.

NET landscape. The crux of it is, you write a small, specialized function that returns a Boolean and takes a ByRef parameter for the return value — like this:. The pattern comes from methods like bool Int TryParse string, out Int32 in. NET, where an exception-throwing Int32 Int This pattern is especially useful to simplify error handling and replace it with standard flow control, like If statements.

For example you could have a TryFind function that takes a Range object along with something to find in that range, invokes Range. Keep the Try prefix for methods that make you dodge that proverbial error-handling bullet. Or if the return values are so closely related they could be expressed as one thing , consider extracting them into a small class.

The GridCoord class in the OOP Battleship project is a great example of this: systematically passing X and Y values together everywhere quickly gets old, and turning them into an object suddenly gives us the ability to not only pass them as one single entity, but we also get to compare it with another coordinate object for equality or intersection, or to evaluate whether that other coordinate is adjacent; the object knows how to represent itself as a String value, and the rest of the code consumes it through the read-only IGridCoord interface — all that functionality would have to be written somewhere else , if X and Y were simply two Long integer values.

Late binding is why.

Learn Visual Basic 6.0- Frame Control,Check Box and Option Buttons- Quick and easy

But in the meantime, you can still benefit from writing modern VBA code that passes the Option Strict rules at least as far as late binding is concerned … and essentially eliminate the possibility for error to ever be raised in your code. If the ProgID does not exist in the registry, an error is raised and no object gets created. Application and make it very complicated locate the ProgID in the registry, lookup the parent library, load the library, find the type, create an instance, return that object. ListObjects call succeed in, say, Excel Things get hairy when you start using late binding for libraries that are essentially guaranteed to exist on every Windows machine built this century.

There are dozens of other methods in the Excel object model that return an Object. NET with Option Strict turned on, late-bound member calls are outright forbidden. By systematically declaring explicit types and avoiding member calls against Object , we not only accomplish exactly that — we also…. But using it when an early-bound alternative is available, is abusing the language feature.

For some reason this year VB6 and VB. Code is written to be executed, right? Nothing is wrong with VBA. It is practically impossible to teach good programming to students that have had a prior exposure to BASIC: as potential programmers they are mentally mutilated beyond hope of regeneration. Bad code is on the programmer, not the language. VBA is a full-fledged, mature programming language that has proven itself multiple times over the past 20 years and more.

VBA code can do this too, using interfaces. For the most part, VBA is only as limiting as you make it. Reflection is made possible in. Reflection is extremely powerful, but comes at a cost: it is generally avoided in places where performance matters. NET delegates are an incredibly useful tool to have at your disposal, but we can very well do without, albeit with a little bit more verbose code.

And guess what? Fancypants LINQ code might be very elegant if used well… it can also be a mind-wrecking nightmare , but. NET programmers tend to avoid using it in places where performance matters. Sure exceptions are great, and they can simplify error handling. You might have toyed with interfaces before, but coding against them i. The Visual Basic Editor is. VBA is often said to be an event-driven language: a lot of worksheet automation involves executing code in response to such or such workbook or worksheet event. ActiveX controls such as MSForms. But how does it all work, and can we leverage this event-driven paradigm in our own code too?

But first, what is this paradigm all about? In a procedural paradigm, code executes one statement at a time, top to bottom, in sequence: procedure A gets invoked, procedure A calls procedure B, procedure B completes, execution returns to procedure A, procedure A completes, execution ends. And when that handler completes, execution resumes in the loop body, right where it left off. This mechanism is extremely useful, especially in an object-oriented project, since only objects class modules are allowed to raise and handle events.

In Excel the host document is represented by a Workbook module, named ThisWorkbook ; every worksheet in this workbook is represented by a Worksheet module. Or Me. Controls in the UserForm1 module, inherited from the UserForm class. Or something like it. You can easily see what events are available in any class, using the Object Browser F2 — all events are members represented with a lightning bolt icon:. Notice the VBE generates Private procedures: there is no reason whatsoever to ever make an event handler public.

Event handler procedures are meant to handle events , i. Event handler procedures are always named in a very specific way, just like interface implementations :. Note the underscore: it matters, on a syntactical level. This is why you should avoid underscores in procedure names, and name all procedures in PascalCase.

Adhering to this naming standard will spare you many headaches later, when you start defining and impementing your own interfaces spoiler: your project will refuse to compile if you try implementing an interface that has members with an underscore in their name. Any VBA class module can define its own events, and events may only be defined in a class module remember: document and userform modules are classes.

Defining events is done using the drumroll Event keyword:. The class that defines an event is the provider ; a class that handles that event is a client. The client code needs to declare a WithEvents field — these fields must be early-bound, and the only types available for the As clause are event providers, i.

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Last December we lost a very valued contributor and friend. Next release the Rubberduck splash screen will be in his memory: that devil ducky was his online avatar. We miss you ThunderXFrame , rest in peace. See the release notes for more information. This release introduces Spanish language support.

German, French, and Czech translations have also been updated. Nothing would make us happier than helping you help us translate Rubberduck! See contributing. The Test Explorer has had a rather impressive facelift, Inspection Results are now much easier to review, navigate and filter. Next release will include a few new inspections, including one that locates obsolete While Wend loops, and suggests to rewrite them as Do While Loop blocks, which can be exited with an Exit Do statement, whereas While loops can only be prematurely exited without throwing an error by an inelegant GoTo jump.

You may have seen the Introducing the Reference Explorer announcement post last autumn — well, the new feature is now field-tested, works beautifully, instinctively, and is ready for prime time. Behold, the new Code Explorer :. Note that rendering lots of search results in a toolwindow will require confirmation if there are too many results to display. The months to come will see further enhancements in several areas; there are several pull requests lined up already — stay tuned, and keep up with the pre-release builds by watching releases on GitHub!

Add ' End Sub The problem is the implicit dependency in ActiveWorkbook. End Sub As a result, procedures explicitly tell their callers what their dependencies are. Dependencies can be hard to find. DoStuff ' End Sub In any case, correctly identifying all the dependencies of a procedure is definitely the hardest part of DI. Method Injection We use method injection when we pass dependencies around as parameters to a method of an object.

End Sub You would inject a parameter that way if no other method in that class would love to share that dependency — in which case you would preferably inject the dependency at the class level, and have one less parameter to every method that would otherwise need it. Assert statements are perfect for this, since that kind of bug should be caught early on: Debug. Assert Not this. Thing Is Nothing 'execution stops if expression is false this. Thing is safe to invoke members against Alternatively, raise a custom error that explains that the Thing property needs to be assigned before DoSomething can be invoked.

Where are all things created? NewGame GridViewAdapter. Create view , randomizer End Sub The controller has other dependencies that should be injected as well. Create grid, RandomShotStrategy. Create rng Case AIDifficulty. Create grid, FairPlayStrategy. Create grid, MercilessStrategy. Create rng End Select End Select If we injected the IPlayer implementations from the start, we would be creating the players before the game even knows on which grid each player is playing, or whether a human player is even involved.

Connection result. Create grid, difficulty If the difficulty is AIDifficulty. NET-specifics removed : Default properties can result in a small reduction in source code-characters , but they can make your code more difficult to read. Sounds terrible. Why would Rubberduck have a DefaultMember annotation then? What is a class? Metadata In order to define a class , a class module needs to contain metadata , information that VBA will use when it needs to create an object.

There are several ways objects can come into existence in VBA. Auto-instantiated objects declared with As New , like the default instance of class modules with a PredeclaredId attribute set to True , are re-created whenever they are no longer in scope but suddenly need to exist again: Private Sub Test Dim foo As New Class1 foo. Members The members of a class are the fields module variables , properties, and methods of the class — whether private or public. Let-coercion happens when you try to evaluate an object as a value expression, for example: Debug. Range "A1:A10" 'ambiguous: is rng the Range or its default value?

Events Easily the very first aspect of writing VBA code we are exposed to, event handler procedures are defined by a special implicit interface that we specify in VBA code using the Event keyword in a class module. We can handle Workbook events in the ThisWorkbook document class module, because the code of ThisWorkbook already includes every member of a Workbook class, even before we write a single line of code in it: Debug.

Class1 module handling Workbook events for a given Workbook object reference. End Sub The Event and WithEvents keywords provide language-level assistance with the otherwise relatively complex wiring-up of callbacks. ListObjects "Table1" ' Print Me. ListObjects 1. Name ' error "object required"