In Unity, how does Unity magically call all "Interfaces"?

You can use reflection to get all types in an assembly that implements a specific interface and then instantiate those types and call the methods on those instances through the interface.

var types = this.GetType().Assembly.GetTypes()
foreach (var type  in types)
    var instance = (IGetNews) Activator.CreateInstance(type);

When it comes to XXXUpdate, OnCollisionXXX and other MonoBehaviours, the way Unity registers is not reflection as it has been widely believed but some internal compilation process.


No, Unity doesn’t use System.Reflection to find a magic method every time it needs to call one.

Instead, the first time a MonoBehaviour of a given type is accessed the underlying script is inspected through scripting runtime (either Mono or IL2CPP) whether it has any magic methods defined and this information is cached. If a MonoBehaviour has a specific method it is added to a proper list, for example if a script has Update method defined it is added to a list of scripts which need to be updated every frame.

During the game Unity just iterates through these lists and executes methods from it — that simple. Also, this is why it doesn’t matter if your Update method is public or private.

In the case of an interface, I would assume it does a bit more since the interface is required. Else, you would just add the method like any other MonoBehaviour methods.

My assumption (that could be wrong), it uses a basic GetComponents on this GameObject. Then iterate the resulting array and call the method that HAS TO BE implemented since it is from the interface.

You could reproduce the pattern with:

NewsData data;
if(GetNews(out data))
    IGetNews [] getNews = data.gameObject.GetComponents<IGetNews>();
    foreach(IGetNews ign in getNews){ ign.SomeNews(); }

GetNews is a method that checks if some news should be sent to the object. You could think of it like Physics.Raycast that assigns values to a RaycastHit. Here it fills a data reference if that object is meant to receive news for any valid reasons.