c# - Converting from an interface to an object that implements the interface? -

i have interface implemented several different objects. trying write method in c# accept interface object parameter , convert parameter object implements don't have write same function several different types. such as:

class unappliedcashdetails implements interface itransactiondetail.

constructor issbatch:

public issbatch(list<itransactiondetail> details)
  
public static issbatch getnextreceiptbatch() {      list<unappliedcashdetail> details = new list<unappliedcashdetail>();
  
    /`*`some code here populate list`*`/                  return = new issbatch(details); 
  
}
  

c# not this. trying use interface wrong or not casting correctly?

thanks!

you're passing list<unappliedcashdetail> constructor accepts list<itransactiondetail>. unappliedcashdetail may implement itransactiondetail, type of variance not supported c#. consider inside constructor (or other method) attempt add instance of someothertransactiondetail details list, except details list should really accept unappliedcashdetail, per declaration.

to make code work, need change declaration

list<itransactiondetail> details = new list<itransactiondetail>();       /* code here populate list */                   return new issbatch(details); 

or change constructor accept ienumerable<itransactiondetail>, in case original list<unappliedcashdetail> declaration work. variance supported ienumerable<t> (note: c# 4), since sequence , cannot added to, deleted from, etc., there's no possibility of trying add appliedcashdetail instance sequence of unappliedcashdetail objects.