Add Item into a generic List in C#

Question

I tried to insert an object into a generic BindingList. But if I try to add a specific object the compiler says: "Argument type ... is not assignable to parameter type"

private void JoinLeaveItem<T>(BindingList<T> collection)
    {

        if (collection.GetType().GetGenericArguments()[0] == typeof(UserInformation))
        {
            var tmp = new UserInformation();
            collection.Add(tmp);
        }
    }

Please help me

Why use a generic collation if you are using a specific type UserInformation? — Oded
– Oded, Commented May 4, 2012 at 8:58
Because this code is not complete ... I would like to add sometihing like — user1374495
– user1374495, Commented May 4, 2012 at 9:13
OK. How are GroupInformation and UserInformation related to each other? Is there an inheritance hierarchy between them and any other type you want to add to the collection? — Oded
– Oded, Commented May 4, 2012 at 9:16
No hierarchy and yes I would like to be able to but any Object into this collection... — user1374495
– user1374495, Commented May 4, 2012 at 9:23

vidstige · Accepted Answer · 2012-05-04 10:54:06Z

1

You cannot have objects of two different types that does not have a common anscestor in a strongly typed list. That is: In your case you will need to different collections unless your two (or more) classes have a common base class.

Try creating overloads instead, like this

private void JoinLeaveItem(BindingList<UserInformation> collection)
{
    collection.Add(new UserInformation());
}

private void JoinLeaveItem(BindingList<GroupInformation> collection)
{
    collection.Add(new GroupInformation());
}

Use it like this

JoinLeaveItem(userInformationCollection)
JoinLeaveItem(groupInformationCollection)

Note: I've inlined the tmp variable.

edited May 4, 2012 at 10:54

answered May 4, 2012 at 8:58

vidstige

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2 Comments

user1374495 Over a year ago

The idea is that I can but BindingList as UserInformation or GroupInformation as well!

vidstige Over a year ago

@user1374495 nice. glad to help. :) If you find the answer helpful, please mark it as accepted by clicking the green checkbox.

Bob Vale · Accepted Answer · 2012-05-04 09:22:12Z

0

From what you've described in your comments do you want to do something like this....

private void JoinLeaveItem<T>(BindingList<T> collection)  where T: new()
    { 
            var tmp = new T(); 
            collection.Add(tmp); 
    }

EDIT If you want to add extra Tests to limit to only the items you specify you could add a big test at the beginning

private void JoinLeaveItem<T>(BindingList<T> collection)  where T: new()
    { 
        if (typeof(T) == typeof(UserInformation) || typeof(T) == typeof(GroupInformation) 
            var tmp = new T(); 
            collection.Add(tmp); 
        } 
    }

Alternatively you can make a more generic solution via use of an interface.

Define an interface

public interface ILeaveItem { }

Make UserInformation and GroupInformation inherit from it and then use

private void JoinLeaveItem<T>(BindingList<T> collection)  where T: ILeaveItem, new()
    { 
            var tmp = new T(); 
            collection.Add(tmp); 
    }

edited May 4, 2012 at 9:22

answered May 4, 2012 at 9:16

Bob Vale

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3 Comments

user1374495 Over a year ago

Yes but how I can put now specific Objects like UserInformation and or GroupInformations ?

Bob Vale Over a year ago

@user1374495 What do you mean? with this code if BindingList is a collection of UserInformation it will determine the type of T and insert a UserInformation object, if BindingList is a collection of GroupInformation it will insert a GroupInformation object

Bob Vale Over a year ago

@user1374495, from your comments on the question you've said that you want either GroupInformation or UserInformation to appear in the same collection at the same time?

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