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What about making the Register method generic?

public class Mediator
{
    private Dictionary<Messages, Action<object>> registeredCallback =
        new Dictionary<Messages, Action<object>>();

    public void Register<TParam>(Messages message, Action<TParam> callback)
    {
        registeredCallback[message] = p => callback((TParam)p);
    }

    public void Notify(Messages message, object parameter)
    {
        callback(parameter);
    }
}

The typecasting is done inside the Register method, making it invisible to any class using it.

You can also change signature of the GreetUser method so that it takes a User instead of an object as a parameter. By doing so you can call Register like this:

mediator.Register<User>(Messages.UserCreated, GreetUser);

What about making the Register method generic?

public class Mediator
{
    private Dictionary<Messages, Action<object>> registeredCallback =
        new Dictionary<Messages, Action<object>>();

    public void Register<TParam>(Messages message, Action<TParam> callback)
    {
        registeredCallback[message] = p => callback((TParam)p);
    }

    public void Notify(Messages message, object parameter)
    {
        callback(parameter);
    }
}

The typecasting is done inside the Register method, making it invisible to any class using it.

You can also change signature of the GreetUser method so that it takes a User instead of a string as a parameter. By doing so you can call Register like this:

mediator.Register<User>(Messages.UserCreated, GreetUser);

What about making the Register method generic?

public class Mediator
{
    private Dictionary<Messages, Action<object>> registeredCallbacks =
        new Dictionary<Messages, Action<object>>();

    public void Register<TParam>(Messages message, Action<TParam> callback)
    {
        registeredCallbacks[message] = p => callback((TParam)p);
    }

    public void Notify(Messages message, object parameter)
    {
        callback(parameter);
    }
}

Also you can change signature of GreetUser method so the method will take a User. In this case you can call Register like this:

mediator.Register<User>(Messages.UserCreated, GreetUser);

What about making the Register method generic?

public class Mediator
{
    private Dictionary<Messages, Action<object>> registeredCallback =
        new Dictionary<Messages, Action<object>>();

    public void Register<TParam>(Messages message, Action<TParam> callback)
    {
        registeredCallback[message] = p => callback((TParam)p);
    }

    public void Notify(Messages message, object parameter)
    {
        callback(parameter);
    }
}

The typecasting is done inside the Register method, making it invisible to any class using it.

You can also change signature of the GreetUser method so that it takes a User instead of an object as a parameter. By doing so you can call Register like this:

mediator.Register<User>(Messages.UserCreated, GreetUser);

What about making the Register method generic?

public class Mediator
{
    private Dictionary<Messages, Action<object>> registeredCallbacks =
        new Dictionary<Messages, Action<object>>();

    public void Register<TParam>(Messages message, Action<TParam> callback)
    {
        registeredCallbacks[message] = p => callback((TParam)p);
    }

    public void Notify(Messages message, object parameter)
    {
        foreach (var callback in registeredCallbacks[message])
        {
            callback(parameter);
        }
    }
}

Also you can change signature of GreetUser method so the method will take a User. In this case you can call Register like this:

mediator.Register<User>(Messages.UserCreated, GreetUser);

What about making the Register method generic?

public class Mediator
{
    private Dictionary<Messages, Action<object>> registeredCallbacks =
        new Dictionary<Messages, Action<object>>();

    public void Register<TParam>(Messages message, Action<TParam> callback)
    {
        registeredCallbacks[message] = p => callback((TParam)p);
    }

    public void Notify(Messages message, object parameter)
    {
        callback(parameter);
    }
}

Also you can change signature of GreetUser method so the method will take a User. In this case you can call Register like this:

mediator.Register<User>(Messages.UserCreated, GreetUser);