Question

I’m still learing VB.NET and usually I just google my questions, but this time I really don’t know what to look for so I’ll try here.

Trying to write a function that takes the cache key as a parameter and returns the cached object. No problems there, but I can’t figure out how to pass the type into the function to use with TryCast, so that I don’t have to do that with the returned result.

Here is my function so far, the ??? is to be replaced with the type that is passed into the function somehow.

Public Function GetCache(ByVal tag As String) As Object     Dim obj As Object = Nothing     Dim curCache As Object = TryCast(System.Web.HttpContext.Current.Cache(tag), ???)     If Not IsNothing(curCache) Then         Return curCache     Else         Return Nothing     End If End Function 

Am I doing this completely wrong or am I just missing something?

Answer 1

Use a generic:

Public Function GetCache(Of T)(ByVal tag As String) As T     Return CType(System.Web.HttpContext.Current.Cache(tag), T) End Function 

update:
Edited to use CType, because trycast only works with reference types. However, this could throw an exception if the cast fails. You can either handle the exception, check the type before making the cast, or limit your code to reference types like this:

Public Function GetCache(Of T As Class)(ByVal tag As String) As T     Return TryCast(System.Web.HttpContext.Current.Cache(tag), T) End Function