How to use Generics to access property

Question

I have a List of two different objects i.e.

List<Customer> Customers;
List<Retailer> Retailers;

I have a method which if i pass in the List with the appropriate type separately everything works.

I thought to try Generics to see if i can have one method to do two tasks i.e. Pass in the type of List and it would iterate through the list and get the record and take whatever action necessary.

        private T AddRecord<T>(List<T> ListofRecords)
        {
            foreach (T rec in ListofRecords.Records)
            {
                Object ob = GetRecord(rec.Id);
            }
        }

The issue i'm coming across is that rec (the variable for the foreach loop) doesnt know what type it is so i cant get to the ID property.

How should i be doing this?

By letting both classes implement the same interface containing the Id property, and constraining your generic type to that interface. See duplicate but ignore the reflection answer. — CodeCaster, Sep 20 '19 at 15:58
What is `ListOfRecords.Records` supposed to be? Do you have a class somewhere that has a `Records` property? — 15ee8f99-57ff-4f92-890c-b56153, Sep 20 '19 at 16:00

score 1 · Answer 1 · answered Sep 20 '19 at 15:58

1

Both Customer and Retail must share the same base class ( or implement the same interface ) having the property Id. Then in your function:

 private T AddRecord<T>(List<T> ListofRecords) where T:YourBaseClass
        {
            foreach (T rec in ListofRecords)
            {
                Object ob = GetRecord(rec.Id);
            }
        }

with where T: you sentence that T must derive ( or implement ) your base class (interface ) so compiler can be aware of the existence of the Id property.

answered Sep 20 '19 at 15:58

Felice Pollano

32,832
9
75
115

Ok... So this is a normal method within a console app, so i cant use it since it doesnt have a base class? – Computer Sep 20 '19 at 16:01
1

@Computer base class ( or interface ) is about Customers and Retailers – Felice Pollano Sep 20 '19 at 16:02

score 1 · Answer 2 · answered Sep 20 '19 at 15:59

If you have a common ancestor, You can limit T to that using the where keyword -

interface IHasId
{
    int Id { get; }
}

private T AddRecord<T>(List<T> listofRecords) where T: IHasId
{
    foreach (var rec in listofRecords)
    {
       var theId = rec.Id;
    }
    ...
}

How to use Generics to access property

2 Answers2