VB.NET: Lanzar eventos de la clase base desde una clase derivada

Supongamos que:

  1. Tenemos una clase que queremos desdoblar en subclases
  2. La futura clase base tiene eventos
  3. El refactoring nos lleva a la necesidad de que desde una clase derivada haya que hacer un RaiseEvent de un evento de la clase base.

Cuando intentemos hacer lo indicado en el punto 3, nos surgirá un error de compilación diciendo que una clase derivada no puede lanzar eventos de la clase base. Para resolver esto, agregamos un método protected en la clase base que encapsule el RaiseEvent de marras, y en la clase derivada lo invocamos usando MyBase. Así:

En la clase base (Los parámetros son a gusto nuestro): 
Protected Overridable Sub OnMessageGenerated(ByVal NewSender As Object, ByVal NewMessage As String)
    RaiseEvent MessageGenerated(NewSender, New MessageEventArgs(NewMessage))
End Sub
Y en la clase derivada 
'Hacer cosas...
'Quiero lanzar el evento de la clase base
MyBase.OnMessageGenerated( Me, "Message" )
'Hacer mas cosas...
Referencias: Post de Mark Gilbert

Comments

Post a Comment

Popular posts from this blog

VB.NET: Raise base class events from a derived class

Spanish version / Versión en Español Say we: Have a class we want to divide into subclasses The future base class has events The refactoring leads us to the need of raising an event declared in the base class, from a derived class. When we try to do point 3, we will get a compile error saying that a derived class cannot raise events from a base class. To get around this, we add a protected method in the base class which encapsulates the RaiseEvent call, and call that method from the derived class using MyBase. This way: In the base class (parameters as needed): Protected Overridable Sub OnMessageGenerated(ByVal NewSender As Object, ByVal NewMessage As String) RaiseEvent MessageGenerated(NewSender, New MessageEventArgs(NewMessage)) End Sub And in the derived class: 'Do stuff 'Raise base class event MyBase.OnMessageGenerated( Me, "Message" ) 'Do more stuff... References: Mark Gilbert post
Keep reading

Apache Kafka - I - High level architecture and concepts

Image
Spanish version / Versión en Español First of all, what is Apache Kafka ? An initial definition for it is "a high-throughput distributed messaging system". Breaking this down a bit: High throughput: One of the main goals of Kafka is to process as much messages per unit of time as possible, in a scalable and fault-tolerant way. For example, LinkedIn , which is where Kafka originated, needs to achieve throughputs in the order of 20 million messages per second and 3 GB of data per second. Distributed messaging system: In a generic distributed system , networked computers work together for a common goal. In Kafka's case, that goal is to send data from points A 1 , A 2 , ... A N , to B 1 , B 2 , ... B M . A common benefit of this kind of system, which is crucial to Kafka's success, is horizontal scalability : the ability to handle higher and higher volumes of data by adding nodes to the system (not to be confused with  vertical scalability , whic
Keep reading

C++/CLI: Convert a String to BSTR or some other nasty stuff

Spanish version / Versión en Español This is very usual when replacing a COM interface with a C++/CLI wrapper (Guess who's doing that?). That usually leads to the need to convert a .NET string (System::String^) to a BSTR, or a std::string. Luckily, .NET provides some handy conversion functions for this. They save us the hassle of creating buffers, releasing them and whatnot. Among them are the marshal_as functions and the marshal_context class. Here's the lowdown for when to use which: Overview of Marshalling in C++
Keep reading