/// <summary>
/// Asynchronously deregisters a handler.
/// </summary>
/// <param name="handlerFactory">The handler to deregister.</param>
/// <returns>
/// A task representing the asynchronous operation.
/// The value of the <see cref="Task{TResult}.Result"/> parameter contains a boolean value
/// indicating whether the handler was actually found and deregistered.
/// </returns>
/// <exception cref="ArgumentNullException">Thrown if <paramref name="handlerFactory"/> is null.</exception>
public async Task <bool> DeregisterAsync(IContextualProvider <THandler> handlerFactory)
{
if (handlerFactory == null)
{
throw new ArgumentNullException(nameof(handlerFactory));
}
Debug.Assert(_handlerStack != null);
Debug.Assert(_lock != null);
using (await _lock.LockAsync())
{
if (_handlerStack.IsEmpty)
{
return(false);
}
var tos = _handlerStack.Last();
Debug.Assert(tos != null);
if (handlerFactory.Equals(tos))
{
if (handlerFactory is IDeactivationNotifyable deactivationNotifyable)
{
await deactivationNotifyable.NotifyDeactivationAsync();
}
// Handler stack will be empty afterwards
if (_handlerStack.Count == 1)
{
await _dispatchForwarding.UnregisterForwardingAsync();
}
else if (_handlerStack[_handlerStack.Count - 2] is IActivationNotifyable activationNotifable)
{
await activationNotifable.NotifyActivationAsync();
}
_handlerStack = _handlerStack.RemoveAt(_handlerStack.Count - 1);
return(true);
}
var newStack = _handlerStack.Remove(handlerFactory);
if (newStack == _handlerStack)
{
return(false);
}
_handlerStack = newStack;
return(true);
}
}
/// <summary>
/// Asynchronously deregisters a handler.
/// </summary>
/// <param name="handlerFactory">The handler to deregister.</param>
/// <returns>
/// A task representing the asynchronous operation.
/// The value of the <see cref="Task{TResult}.Result"/> parameter contains a boolean value
/// indicating whether the handler was actually found and deregistered.
/// </returns>
/// <exception cref="ArgumentNullException">Thrown if <paramref name="handlerFactory"/> is null.</exception>
public async Task <bool> DeregisterAsync(IContextualProvider <THandler> handlerFactory)
{
if (handlerFactory == null)
{
throw new ArgumentNullException(nameof(handlerFactory));
}
Debug.Assert(_handlers != null);
Debug.Assert(_lock != null);
using (await _lock.LockAsync())
{
if (!_handlers.Contains(handlerFactory))
{
return(false);
}
var handlers = _handlers.Remove(handlerFactory);
if (handlers.IsEmpty)
{
await _dispatchForwarding.UnregisterForwardingAsync();
}
if (handlers.IsEmpty && handlerFactory is IDeactivationNotifyable deactivationNotifyable)
{
await deactivationNotifyable.NotifyDeactivationAsync();
}
_handlers = handlers;
if (_handlers.Count == 1 && _handlers.First() is IActivationNotifyable activationNotifyable)
{
await activationNotifyable.NotifyActivationAsync();
}
return(true);
}
}