FingerGestures

Here, we subscribe to the 3 drag events in the OnEnable() method that is automatically called by Unity when our script gets enabled. The ”+=” notation is a syntactic sugar specific to .NET events. It simply means “call this method when that event is fired”. Here for instance, we tell the system to call the FingerGestures_OnDragBegin() method on our TutorialMethod1 instance when the OnDragBegin event located on the FingerGestures singleton is fired. In more technical terms, this FingerGestures_OnDragBegin() method is referred to as a callback method or event handler.The signature of the callback method you use to subscribe to an event must match the signature of this particular event. For instance, the OnDragEnd event expects a callback method with exactly one argument of type “Vector2” (for the finger position). Trying to subscribe to the OnDragEnd event using a method with a different signature will generate a compilation error.

When subscribing to events, it's also important to remember to unsubscribe from them when you no longer can or need/want to receive notifications from them. It is particularly important in the case of the FingerGesture singleton events, as it persists between scene transitions. If you do not unsubscribe from the events before your object is destroyed, the FingerGestures singleton will still have that object on its list of event recipients, and a null reference error will occur as a consequence. That is why we unsubscribe from the drag events in the OnDisable() method that is automatically called by the Unity engine when the script is disabled (which also happens before the host game object is destroyed).