N Layer .Net Message management

Question

Im developing a N Layer web application (UI/Service/DAL).

When in calling a certain service, inside the service layer sometimes theres an event that requires user notification.

How should I pass these messages from the service layer to the UI layer?

It is very important to notice that these messages are not errors but only notifications of certain events.

Answer 1

You can achieve it with Dependency Injection. Say that you have a generic interface of IUserNotificator like this:

interface IUserNotificator{
    //message type can be Warning, Success, Error or Confirmation
    void Notify(string message, MessageType messageType);
}

And your service class doing something like this:

class Service{
    // construtor injection of IUserNotificator

    void DoSomething(){
        // doing something
        if(error){
            IUserNotificator.Notify("There is error", MessageType.Error);
        }
        else{
            IUserNotificator.Notify("Operation success", MessageType.Success);
        }
    }
}

This way, you can have different implementations at UI level. Say that you have a C# winform app:

class MessageBoxUserNotificator : IUserNotificator{
    void Notify(string message, MessageType messageType){
        if(messageType == MessageType.Error){ 
            MessageBox.Show(message, "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        else{
            MessageBox.Show(message, "Notification");
        }
    }
}

For more flexibility the class can be expanded using decorator for multiple notificator at one operation.