Question

Imagine I have a C# app sitting on a server somewhere that is creating instances of the Item class and publishing them on a messaging service.

class Item
{
    public int ID1, ID2, ID3;
    public double Value1, Value2, Value3;
}

Now I have another C# app on a desktop somewhere listening to these messages. I want to be able to create callbacks based on specified values of the ID# fields. For example, “call this method whenever a message comes in where ID1 = 2, ID2 = 160, and ID3 = anything”. I think this would be straightforward if I used string key-value pairs, but ideally I could do this without giving up static typing. I imagine this requires reflection, but I’m not entirely sure where to start.

I’m picturing the app creating an instance of Item with the required ID# values (let’s say -1 means unspecified), and passing that into a RegisterCallback method of some object ItemListener. Then whenever ItemListener receives a new Item message, it can check for any callbacks that match, and act accordingly. Is this a reasonable design? Any suggestions on what to look at to implement it?

Answer 1

class ConditionalCallback()
{
     public Predicte<Item>   Predicate {get; set;}
     public Action<Item>     Callback  {get; set;}
}

List<ConditionalCallback> callbacks = new List<ConditionalCallback>();

public AddCallBack(Predicte<Item> pred, Action<Item> callback)
{
    callbacks.Add(new ConditionalCallback { 
                              Predicate = pred, 
                              Callback = callback
                               });
}


void HandleItem(Item item)
{
     foreach(var cc in callbacks)
         if (cc.Predicate(item))    
             cc.Callback(item);
}

// 

AddCallBack( i=> i.ID1 = 2 && i.ID2 = 160 && i.ID3 = anything", MyCallback);