在C＃.NET的方法签名中传递“ this”的VB.NET等价方式是什么？

Question

My question stems from the code samples from Wrox Press's Professional ASP.NET Design Patterns. The code downloads are in C#, however, I'm working through the samples in VB.

I would appreciate if someone could explain what 'this' means in the following method signature, and what the equivalent method signature would be in VB.NET.

Here is the code sample (from p.51) in question:

public static void Apply(this IList<Product> products, IDiscountStrategy discountStrategy) { ... }

Answer 1

This is an extension method they are implemented in VB.NET

The syntax you need is:

<Extension()> 
Public Sub Print(ByVal aString As String)
    Console.WriteLine(aString)
End Sub

for example

Answer 2

This is an extension method. The this indicates that you can call the static method with the following syntax:

  products.Apply(strategy);

as opposed to to

  WhateverClass.Apply(products, strategy);

In VB you would decorate the method with the Extension attribute

  <Extension()>
  Sub Apply(ByVal products as IList<Product>, ByVal discountStrategy as IStrategy)
    ...

See http://msdn.microsoft.com/en-us/library/bb384936.aspx for more

Answer 3

For an extension method in VB you use the ExtensionAttribute

<Extension()>
Public Sub Apply(IList(of Product) products, IDiscountStrategy discountStrategy)
    '...
End Sub

The above syntax may not be 100%

Answer 4

I think it's for extension methods. Not sure how those are implemented in VB.NET.

Answer 5

the this used thusly denotes an extension method. you now have an Apply method that can be used on any IList<Product> as if it were a member method, so you can call it like

list.Apply(discountStrategy);

instead of like

Apply(list, discountStrategy);

Its really useful to avoid having to name that method ApplyDiscountStrategyToListOfProducts , and having tons of Apply*ToListOf* methods.

The VB equivalent is here: http://msdn.microsoft.com/en-us/library/bb384936.aspx