c# - Generic type conversion in generic method -

i have following classes (some of them in prism framework , cannot changed):

public abstract class networkeventbase<t> : compositepresentationevent<t> t : networkeventpayload { } public class networkeventpayload { } public class testevent : networkeventbase<testpayload> { } public class testpayload : networkeventpayload { }  // following classes prism classes: public class compositepresentationevent<tpayload> : eventbase { } public abstract class eventbase { } 

now need convert instance of testevent base class networkeventbase inside decorator ieventaggregator. ieventaggregator looks like:

public interface ieventaggregator {     teventtype getevent<teventtype>() teventtype : eventbase, new(); } 

now in decorator try convert this:

public class messagebusadapterinjectordecorator : ieventaggregator {     ...      public teventtype getevent<teventtype>() teventtype : eventbase, new()     {         var aggregatedevent = this.eventaggregator.getevent<teventtype>();         var networkevent = aggregatedevent networkeventbase<networkeventpayload>;          if (networkevent != null)         {             networkevent.messagebusadapter = this.messagebusadapter;         }          return aggregatedevent;     } } 

however, networkevent null, when runtime type of aggregatedevent testevent.

you seem hope class called networkeventbase<t> covariant in t. generic classes can't covariant in c# (generic interfaces can).

see other threads on issue.