EventAggregator Helper通用方法

Question

Why this gives a compiler error?

public class EventAggregationHelper {

    public static SubscriptionToken SubscribeToEvent<T>( IEventAggregator eventAggregator ) where T : EventBase {

        T evt = eventAggregator.GetEvent<T>();
        //T evt = eventAggregator.GetEvent<T>();
        return null;
    }
}

The error is:

Severity Code Description Project File Line Suppression State Error CS0310 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'TEventType' in the generic type or method 'IEventAggregator.GetEvent()' EntitySetGridTWPF D:\\DEVELOPER.NET\\Comercial\\EntityBookCommon\\EntitySetGridTWPF\\EventAggregation\\EventAggregationHelper.cs 9 Active

on the line:

T evt = eventAggregator.GetEvent<T>();

I've used this approach for calling other generic methods before and has worked. What has GetEvent so special?

Thanks in advance.

Answer 1

IEventAggregator.GetEvent has a new() constraint, which means that your subscription also needs to add the new() constraint and that also needs to be fulfilled by your implementation class T , which must have a public parameterless (default) constructor (and must not be abstract.)

public static SubscriptionToken SubscribeToEvent<T>
            (IEventAggregator eventAggregator) where T : EventBase, new() {