Further reading

To get a better understanding of the observer pattern, please take a look at https://docs.microsoft.com/en-us/dotnet/standard/events/observer-design-pattern.

The following is a good article that talks about declaring, initiating, and using delegates. Samples can also be found there: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/how-to-declare-instantiate-and-use-a-delegate.