public static IDisposable Attach <T, THandle>(T obj, Expression <Func <T, string> > selectEventHandlerName, THandle handler)
where T : class
where THandle : Delegate
{
if (obj is null)
{
throw new ArgumentNullException(nameof(obj));
}
var eventInfo = selectEventHandlerName.GetMember <EventInfo>();
if (eventInfo is null)
{
var constEx = selectEventHandlerName.EnumerateExpressions()
.OfType <ConstantExpression>()
.FirstOrDefault();
string?eventName = constEx?.Value?.ToString();
if (string.IsNullOrEmpty(eventName))
{
// We can't find it!
throw new ArgumentException("The given expression doesn't contain enough information to find an Event", nameof(selectEventHandlerName));
}
eventInfo = typeof(T).GetEvent(eventName, Reflect.InstanceFlags);
if (eventInfo is null)
{
// Can't find it
throw new ArgumentException($"{typeof(T).Name} does not have an instance event named '{eventName}'",
nameof(selectEventHandlerName));
}
}
//Cast the delegate to the correct type
var castHandler = Delegate.CreateDelegate(eventInfo.EventHandlerType !, handler.Target, handler.Method);
//Add it to the event handler
eventInfo.AddEventHandler(obj, castHandler);
//Create our remove action
void Remove() => eventInfo.RemoveEventHandler(obj, castHandler);
//Return it in a dispose action
return(Disposable.Action(Remove));
}