/// <summary>
/// Subscribes to the specified event.
/// </summary>
/// <param name="target">The object that publishes the event.</param>
/// <param name="eventInfo">The event to which we subscribe.</param>
public EventArgsTask(object target, EventInfo eventInfo)
{
_tcs = new TaskCompletionSource <TEventArgs>();
_target = target;
_eventInfo = eventInfo;
var eventCompletedMethod = ReflectionShim.GetMethod(GetType(), "EventCompleted");
_subscription = ReflectionShim.CreateDelegate(eventInfo.EventHandlerType, this, eventCompletedMethod);
eventInfo.AddEventHandler(target, _subscription);
}
/// <summary>
/// Gets a task that will complete the next time an event is raised. The event type must follow the standard <c>void EventHandlerType(object, TResult)</c> pattern. Be mindful of race conditions (i.e., if the event is raised immediately before this method is called, your task may never complete).
/// </summary>
/// <param name="target">The object that publishes the event.</param>
/// <returns>The event args.</returns>
public static Task <TResult> FromEvent(object target)
{
// Try to look up an event that has the same name as the TResult type (stripping the trailing "EventArgs").
var type = target.GetType();
var resultType = typeof(TResult);
var resultName = resultType.Name;
if (resultName.EndsWith("EventArgs", StringComparison.Ordinal))
{
var eventInfo = ReflectionShim.GetEvent(type, resultName.Remove(resultName.Length - 9));
if (eventInfo != null)
{
return(new EventArgsTask <TResult>(target, eventInfo).Task);
}
}
// Try to match to any event with the correct signature.
EventInfo match = null;
foreach (var eventInfo in ReflectionShim.GetEvents(type))
{
var invoke = ReflectionShim.GetMethod(eventInfo.EventHandlerType, "Invoke");
if (invoke.ReturnType != typeof(void))
{
continue;
}
var parameters = invoke.GetParameters();
if (parameters.Length != 2 || parameters[0].ParameterType != typeof(object) || parameters[1].ParameterType != resultType)
{
continue;
}
if (match != null)
{
throw new InvalidOperationException("Found multiple matching events on type " + target.GetType().FullName);
}
match = eventInfo;
}
if (match == null)
{
throw new InvalidOperationException("Could not find a matching event on type " + target.GetType().FullName);
}
return(new EventArgsTask <TResult>(target, match).Task);
}