Overrides in VB.NET - Using VB.NET Series

Supersedes in VB.NET - Using VB.NET Series This is one of a smaller than usual arrangement that covers the distinctions in Overloads, Shadows, and Overrides in VB.NET. This article covers Overrides. The articles that spread the others are here: - Overloads-Shadows These methods can be immensely confounding; there are a ton of blends of these watchwords and the fundamental legacy choices. Microsofts own documentation doesnt start to do the theme equity and there is a great deal of terrible, or outdated data on the web. The best counsel to be certain that your program is coded accurately is, Test, test, and test once more. In this arrangement, well gander at them each in turn with accentuation on the distinctions. Supersedes What Shadows, Overloads, and Overrides all share for all intents and purpose is that they reuse the name of components while changing what occurs. Shadows and Overloads can work both inside a similar class or when a class acquires another class. Abrogates, in any case, must be utilized in an inferred class (once in a while called a youngster class) that acquires from a base class (now and then called a parent class). Furthermore, Overrides is the mallet; it lets you altogether supplant a strategy (or a property) from a base class. In the article about classes and the Shadows catchphrase (See: Shadows in VB.NET), a capacity was added to show that an acquired methodology could be referenced. Open Class ProfessionalContact ... code not demonstrated ... Open Function HashTheName( ByVal nm As String) As String Return nm.GetHashCode End Function End Class The code that launches a class got from this one (CodedProfessionalContact in the model) can call this strategy since its acquired. In the model, I utilized the VB.NET GetHashCode strategy to keep the code straightforward and this restored a genuinely pointless outcome, the worth - 520086483. Assume I needed an alternate outcome returned rather be that as it may, - I cannot change the base class. (Possibly the sum total of what I have is incorporated code from a merchant.) ... also, ... - I cannot change the calling code (Maybe there are a thousand duplicates and I cannot refresh them.) In the event that I can refresh the determined class, at that point I can change the outcome returned. (For instance, the code could be a piece of an updatable DLL.) There is one issue. Since its so far reaching and amazing, you must have authorization from the base class to utilize Overrides. Be that as it may, very much structured code libraries give it. (Your code libraries are on the whole very much structured, right?) For instance, the Microsoft gave work we simply utilized is overridable. Heres a case of the sentence structure. Open Overridable Function GetHashCode As Integer With the goal that watchword must be available in our model base class also. Open Overridable Function HashTheName( ByVal nm As String) As String Superseding the strategy is presently as straightforward as furnishing another one with the Overrides watchword. Visual Studio again gives you a showing start to filling in the code for you with AutoComplete. At the point when you enter ... Open Overrides Function HashTheName( Visual Studio includes the remainder of the code naturally when you type the initial bracket, including the arrival articulation which just calls the first capacity from the base class. (In the event that youre simply including something, this is typically something to be thankful for to do after your new code executes in any case.) Open Overrides Function HashTheName( nm As String) As String Return MyBase.HashTheName(nm) End Function For this situation, nonetheless, Im going to supplant the strategy with something different similarly futile just to outline how its done: The VB.NET work that will turn around the string. Open Overrides Function HashTheName( nm As String) As String Return Microsoft.VisualBasic.StrReverse(nm) End Function Presently the calling code gets an altogether unique outcome. (Contrast and the outcome in the article about Shadows.) ContactID: 246 BusinessName: Villain Defeaters, GmbH Hash of the BusinessName: HbmG ,sretaefeD nialliV You can abrogate properties as well. Assume you concluded that ContactID esteems more noteworthy than 123 would not be permitted and should default to 111. You can simply abrogate the property and change it when the property is spared: Private _ContactID As Integer Open Overrides Property ContactID As Integer Get Return _ContactID End Get Set(ByVal esteem As Integer) On the off chance that esteem 123, Then _ContactID 111 Else _ContactID esteem End If End Set End Property At that point you get this outcome when a bigger worth is passed: ContactID: 111 BusinessName: Damsel Rescuers, LTD Coincidentally, in the model code up until this point, whole number qualities are multiplied in the New subroutine (See the article on Shadows), so a whole number of 123 is changed to 246 and afterward changed again to 111. VB.NET gives you, significantly more, control by permitting a base class to explicitly require or deny a determined class to supersede utilizing the MustOverride and NotOverridable catchphrases in the base class. Be that as it may, both of these are utilized in genuinely explicit cases. To begin with, NotOverridable. Since the default for an open class is NotOverridable, for what reason would it be a good idea for you to ever need to indicate it? In the event that you give it a shot the HashTheName work in the base class, you get a language structure mistake, however the content of the blunder message provides you some insight: NotOverridable can't be determined for techniques that don't abrogate another strategy. The default for a superseded strategy is the polar opposite: Overrideable. So on the off chance that you need abrogating to stop there, you need to determine NotOverridable on that technique. In our model code: Open NotOverridable Overrides Function HashTheName( ... At that point if the class CodedProfessionalContact is, thus, acquired ... Open Class NotOverridableEx Acquires CodedProfessionalContact ... the capacity HashTheName can't be overriden in that class. A component that can't be superseded is in some cases called a fixed component. A key piece of the .NET Foundation is to necessitate that the reason for each class is expressly characterized to expel all vulnerability. An issue in past OOP dialects has been called â€Å"the delicate base class.† This happens when a base class includes another strategy with a similar name as a technique name in a subclass that acquires from a base class. The developer composing the subclass didnt plan on abrogating the base class, however this is actually what happens at any rate. This has been known to bring about the call of the injured developer, I didnt transform anything, however my program slammed in any case. In the event that there is a likelihood that a class will be refreshed later on and make this issue, proclaim it as NotOverridable. MustOverride is regularly utilized in what is called an Abstract Class. (In C#, something very similar uses the watchword Abstract!) This is a class that just gives a format and youre expected to fill it with your own code. Microsoft gives this case of one: Open MustInherit Class WashingMachine Sub New() Code to start up the class goes here. End sub Open MustOverride Sub Wash Open MustOverride Sub Rinse (loadSize as Integer) Open MustOverride Function Spin (speed as Integer) as Long End Class To proceed Microsofts model, clothes washers will do these things (Wash, Rinse and Spin) in an unexpected way, so theres no favorable position of characterizing the capacity in the base class. Yet, there is a favorable position in ensuring that any class that acquires this one characterizes them. The arrangement: a theoretical class. On the off chance that you need much more clarification about the contrasts among Overloads and Overrides, a totally unique model is created in a Quick Tip: Overloads Versus Overrides VB.NET gives you considerably more control by permitting a base class to explicitly require or deny an inferred class to abrogate utilizing the MustOverride and NotOverridable watchwords in the base class. Be that as it may, both of these are utilized in genuinely explicit cases. To start with, NotOverridable. Since the default for an open class is NotOverridable, for what reason would it be advisable for you to ever need to indicate it? In the event that you give it a shot the HashTheName work in the base class, you get a linguistic structure blunder, however the content of the mistake message provides you some insight: NotOverridable can't be indicated for techniques that don't abrogate another strategy. The default for an abrogated strategy is the polar opposite: Overrideable. So in the event that you need abrogating to stop there, you need to indicate NotOverridable on that technique. In our model code: Open NotOverridable Overrides Function HashTheName( ... At that point if the class CodedProfessionalContact is, thusly, acquired ... Open Class NotOverridableEx Acquires CodedProfessionalContact ... the capacity HashTheName can't be overriden in that class. A component that can't be abrogated is some of the time called a fixed component. A central piece of the .NET Foundation is to necessitate that the motivation behind each class is expressly characterized to expel all vulnerability. An issue in past OOP dialects has been called â€Å"the delicate base class.† This happens when a base class includes another strategy with a similar name as a technique name in a subclass that acquires from a base class. The developer composing the subclass didnt plan on abrogating the base class, however this is actually what happens in any case. This has been known to bring about the call of the injured developer, I didnt transform anything, yet my program slammed in any case. In the event that there is a likelihood that a class will be refreshed later on and make this issue, pronounce it as NotOverridable. MustOverride is regularly utilized in what is called an Abstract Class. (In C#, something very similar uses the watchword Abstract!) This is a class that just gives a format and youre expected to fill it with your own code. Microsoft give