/// <summary>
/// Resolve a message handler delegate for the message type from multiple sources.
/// This will try resolving a message handler delegate from all sources until a handler
/// who is either not null or not equal to <see cref="Xer.Delegator.NullMessageHandlerDelegate.Instance"/> is found.
/// </summary>
/// <remarks>
/// If no handler is found, an instance of <see cref="Xer.Delegator.NullMessageHandlerDelegate.Instance"/> is returned.
/// Any exceptions thrown by the internal resolvers will be propagated.
/// </remarks>
/// <param name="messageType">Type of message.</param>
/// <returns>Message handler delegate.</returns>
public MessageHandlerDelegate ResolveMessageHandler(Type messageType)
{
try
{
// Resolvers can either be a list of SingleMessageHandlerResolver or MultiMessageHandlerResolver.
foreach (IMessageHandlerResolver resolver in _resolvers)
{
MessageHandlerDelegate messageHandlerDelegate = resolver.ResolveMessageHandler(messageType);
if (messageHandlerDelegate != null &&
messageHandlerDelegate != NullMessageHandlerDelegate.Instance)
{
return(messageHandlerDelegate);
}
}
// Return null handler that does nothing.
return(NullMessageHandlerDelegate.Instance);
}
catch (NoMessageHandlerResolvedException)
{
// If a source has thrown this exception, just rethrow.
throw;
}
catch (Exception ex)
{
throw NoMessageHandlerResolvedException.WithMessageType(messageType, ex);
}
}
/// <summary>
/// Send message to a delegate with one/many handlers.
/// </summary>
/// <typeparam name="TMessage">Type of message.</typeparam>
/// <param name="message">Message to send.</param>
/// <param name="cancellationToken">Optional cancellation token to be passed to handlers.</param>
/// <returns>Asynchronous task which can be awaited for completion.</returns>
public Task SendAsync <TMessage>(TMessage message, CancellationToken cancellationToken = default(CancellationToken)) where TMessage : class
{
if (message == null)
{
throw new ArgumentNullException(nameof(message));
}
Type messageType = message.GetType();
MessageHandlerDelegate messageHandler = _messageHandlerResolver.ResolveMessageHandler(messageType);
if (messageHandler == null)
{
throw NoMessageHandlerResolvedException.WithMessageType(messageType);
}
return(messageHandler.Invoke(message, cancellationToken));
}
/// <summary>
/// Resolve a message handler delegate for the message type and throws an exception if no handler is found.
/// </summary>
/// <param name="messageType">Type of message.</param>
/// <returns>Message handler delegate which invokes all registered handlers.</returns>
/// <exception cref="Xer.Delegator.Exceptions.NoMessageHandlerResolvedException">Throws when no message handler delegate is found.</exception>
public MessageHandlerDelegate ResolveMessageHandler(Type messageType)
{
try
{
MessageHandlerDelegate messageHandler = _messageHandlerResolver.ResolveMessageHandler(messageType);
// Throw if resolved handler is a null message handler.
if (messageHandler == null || messageHandler == NullMessageHandlerDelegate.Instance)
{
throw NoMessageHandlerResolvedException.WithMessageType(messageType);
}
return(messageHandler);
}
catch (Exception ex)
{
throw NoMessageHandlerResolvedException.WithMessageType(messageType, ex);
}
}
