Correct usage of generics in event declaration

问题

I have a data object which I pass around :

public class TimedResult<T>
{
    public ResultRequest Request { get; set; }
    public T Data { get; set; }
    public TimeSpan TimeTaken { get; set; }
}

In my Manager class I have some work done which raises an event :

public void Execute(ResultRequest request)
{
    var result = new TimedResult<DataTable>();
    // fill data object here
    OnResult(result);
}

I have made the OnResult method generic :

protected virtual void OnResult<T>(TimedResult<T> result)
{
    if (Result != null)
        Result(this, result);
}

But how do I make the event declaration generic?

public event EventHandler<TimedResult<T>> Result; // red line under T

How should I be doing this?

回答1:

Event declarations cannot be (open) generic. They can use generic type parameters from the declaring type, but they cannot declare their own generic parameters. So what you want is only possible if the type that declares Result has a T (either directly, or via an outer-type), i.e. if this is SomeManager<T>:

class SomeManager<T> {
     public event EventHandler<TimedResult<T>> Result;
}

then the T is whatever it is from above; in SomeManager<int> it will be an EventHandler<TimedResult<int>> and so on.

回答2:

But how do I make the event declaration generic?
public event EventHandler<TimedResult<T>> Result; // red line under T

The class which declares the whole event should be also generic (i.e. it should have a generic type parameter):

public class X<TEventData>
{
    public event EventHandler<TimedResult<TEventData>> Result; // red line under T
}

Now, depending on your requirements, this will work or not, because if you're looking for raising the event with more than an event data type, you might solve this raising the event using reflection (avoid this).

Or I would suggest that you should design an interface which should define that any given event data shares some members, give that interface as X<TEventData> TEventData type argument, and cast the interface type to a concrete implementation when needed in your event handlers.

来源：https://stackoverflow.com/questions/26177228/correct-usage-of-generics-in-event-declaration

标签

events

generics

delegates

eventargs