list type comparison - advice required

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Im stuck trying to compare two list types. For example consider the below

VB

 public class Test
   private _number as integer

   public property Number as integer
     'get and set code here
   end property
 end class

public class Test2
 Private _number as integer

 public property Number as integer
   'get and set info here
 end property
end class

Now I create two lists one of each type

VB

dim List1 as list(of Test)
dim List2 as list(of Test2)

Im trying to test the lists to make sure they are of the same type before performing a union statement on them both.

in this example that they are both of the type Test

any good material / pointers that I can read upon please :)

SOLUTION FOUND
I found a way around it by taking the first item from each list and comparing their type like so.

dim x as object = list1(0)
dim y as object = List2(0)

if type.equals(x,y) then
 messagebox "they are the same"
end if

Posted 1-Mar-11 5:25am

Simon_Whale

Updated 1-Mar-11 6:17am

Manas Bhardwaj

v3

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Henry Minute 1-Mar-11 11:32am

How are you doing the test?

Simon_Whale 1-Mar-11 11:37am

at the moment this

Dim t As Type = list1.GetType

but I can only see an indication of the class type from the assemblyQualifiedName as that gives

System.Collections.Generic.List`1[[WindowsApplication1.Test, WindowsApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089

Henry Minute 1-Mar-11 11:40am

Maybe a variation on Manas's answer
If TypeOf List1 = TypeOf List2 Then
' Blah blah
End If

Simon_Whale 1-Mar-11 11:47am

you can't do that Henry as you have to

If Typeof List1 is x then
'Blah Blah
End if

Henry Minute 1-Mar-11 11:49am

Bummer!

Simon_Whale 1-Mar-11 12:17pm

Thanks anyway Henry found a solution

I found a way around it by taking the first item from each list and comparing their type like so.

dim x as object = list1(0)
dim y as object = List2(0)

if type.equals(x,y) then
messagebox.show "they are the same"
end if

4 solutions

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Yusuf · Accepted Answer · 2011-03-01T05:35:00

Solution 1

May be one what to handle it is to derive both Test1 and Test2 from base class Test. Then you can check if it is ~~TypeOf~~ GetType(Test) to check if they are of the same type.

Posted 1-Mar-11 5:35am

Yusuf

Comments

Simon_Whale 1-Mar-11 12:13pm

Thanks for the advise

Simon

Manas Bhardwaj · Accepted Answer · 2011-03-01T05:36:00

Solution 2

If I understand correctly, you want to test if the list is of type Test or not. For that, you can do something like this:

VB

If TypeOf List1 Is Test Then
    Console.WriteLine("List1 is Test")
End If

Posted 1-Mar-11 5:36am

Manas Bhardwaj

Comments

Simon_Whale 1-Mar-11 12:13pm

Thanks for the advise found a solution - added to my question above

Sergey Alexandrovich Kryukov · Accepted Answer · 2011-03-01T05:43:00

You're not comparing "types". You're trying to do something with lists of the elements of completely unrelated types. Why?

Even though they are declared using identical code, they are completely different; so their instances are not assignment-compatible. If you want to store them in the same list (as you mentioned union), it can only be a polymorphous list if System.Object — closest common ancestor. In real life, you need just one type, or types having closer common base type.

Even though using these two types makes not sense, you could only compare two different instances of two different types per component (one Number equals to another Number). You can even create comparison operators between the two. You can override object.Equals and object.GetHashCode and than add operators == and !=. You can also define explicit or implicit conversion operators Test in Test2 and Test2 in Test.

In real life the two types make no sense, but I think you just want to understand how it all works.

Good luck,

—SA

Gregory Gadow · Accepted Answer · 2011-03-01T06:02:00

A lot depends on how you define "equal" and what the actual format of the two classes are.

Assuming that Test and Test1 are different names for the same object, you would first compare the lengths of List1 and List2; if they are not the same, they are not equal. Then you would iterate through every object in List1 and compare every element with the corresponding element in the corresponding object in List2.

VB

Public Function AreTheyEqual( _
    ByVal L1 As List(Of Test), _
    ByVal L2 As List(Of Test1) _
) As Boolean

    If L1.Count <> L2.Count Then Return False

    For i As Integer = 0 To L1.Count - 1
        Dim T1 As Test = L1(i)
        Dim T2 As Test1 = L2(i)

        If T1.Property1 <> T2.Property1 Then Return False
        If T1.Property2 <> T2.Property2 Then Return False
        ....
    Next

    Return True
End Function

Things get a bit more challenging if the two classes are different: again, you would need to define what "equals" actually means.

list type comparison - advice required

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