c# - Why can't I cast EntityCollection<TEntity> to ICollection<Object>? -

if try cast object of type entitycollection<mynamespace.models.myentityclass> icollection<object> invalidcastexception.

okay, according docs, entitycollection<tentity> implements icollection<t>, , mynamespace.models.myentityclass must descend object, right? why on earth fail?

fwiw, i'm trying in method can add , remove items might entitycollection or other ilist or iset. need preserve change tracking behavior of entitycollection, because object able commit changes if it's ec.

edit

okay, here's more specifics of i'm doing. i'm deserializing json, , target object can have properties collections--maybe they're entitycollections, maybe not. sake of simplicity, lets members of collection subclasses of entityobject, whether it's entitycollection or not (if understand responses far, i'd have no better luck casting icollection<entityobject> icollection<object>…right?). part run trouble…

foreach (propertyinfo prop in hasmanys) {     // invalidcastexception...     icollection<object> oldhms = (icollection<object>)prop.getvalue(parentobj, null);      jenumerable<jtoken> hmids = links[formatpropname(prop.name)].children();     if (hmids.count() == 0)     {         // no members! clear out!         oldhms.clear();         continue; // breaking early!     }      reltype = prop.propertytype.getgenericarguments()[0];      // actual entities we'll need put relationship...     list<entityobject> newhms = new list<entityobject>();     foreach (jtoken jt in hmids)     {         // ...populate newhms existing entityobjects context...     }          // first, delete missing...         /* got use tolist() make copy, because otherwise missings           * still connected oldhms collection (it's objectquery)          * , can't modify oldhms while enumerating missings.           */         // cast fail too, right? though it's more fixable:         ienumerable<entityobject> missings = ((icollection<entityobject>)oldhms).except(newhms).tolist();         foreach (entityobject missing in missings)         {             oldhms.remove(missing); // 1 of mutable collection operations         }          // add new ones         foreach (entityobject child in newhms)         {             if (!oldhms.contains(child)) // skip if in there             {                 oldhms.add(child); // mutable collection operation             }         }      }  } 

that's bit simplified, have special cases arrays (implement icollection, aren't generics) , other stuff took out. point is, need operate clear, add, , remove on entitycollection itself--if that's is. maybe there's way type of synchronization i'm missing?

read-write collections cannot variant.

take example:

list<myclass> list1 = new list<myclass>();  // assume work icollection<object> list2 = list1;  list2.add(new object()); // ooops. added object list<myclass>! 

in principal kind of casting possible "read-only" interfaces (allowing covariance) or "write-only" interfaces (allowing contravariance).

one "solution" involve wrapper class this:

public class wrapper<t> : icollection<object> {     private readonly icollection<t> collection;     public wrapper(icollection<t> collection)     {         this.collection = collection;     }       public void add(object item)     {         // maybe check if t of desired type         collection.add((t)item);     }      public void clear()     {         collection.clear();     }      public bool contains(object item)     {         // maybe check if t of desired type         return collection.contains((t)item);     }      public void copyto(object[] array, int arrayindex)     {         // maybe check if t of desired type         collection.copyto(array.cast<t>().toarray(), arrayindex);     }      public int count     {         { return collection.count; }     }      public bool isreadonly     {         { return collection.isreadonly; }     }      public bool remove(object item)     {         // maybe check if t of desired type         return collection.remove((t)item);     }      public ienumerator<object> getenumerator()     {         yield return collection;     }      system.collections.ienumerator system.collections.ienumerable.getenumerator()     {         return collection.getenumerator();     } } 

instead of

 entitycollection<mynamespace.models.myentityclass> collection = ...;  icollection<object> generic = collection ; 

you have write:

 entitycollection<mynamespace.models.myentityclass> collection = ...;  icollection<object> generic = new wrapper(collection); 

and adjust wrapper class @ points marked comments how deal type problems.