Getting help online can be difficult. People get mad at you, they do not understand your question, or the answers you get are not correct. What do you do? Well, you watch this video and learn how to ask the right question the right way to get the right results. - Newsletter signup (with exclusive discounts): https://signup.iamtimcorey.com/ (your email will be kept safe and you will not be spammed). - Source Code: https://leadmagnets.app/?Resource=InterfacesInCSharp - Design Patterns as referenced in the video - https://www.youtube.com/watch?v=dhnsegiPXoo 0:00 - Intro 1:06 - Demo application walk-through 4:50 - Explaining the problem: putting instances of different classes (product models) in one list (shopping cart) 7:54 - Creating an interface 12:53 - Implementing the interface 20:29 - List of type Interface 23:43 - Note about items in the List of type Interface: Accessing a Class member not in the contract (Interface) 25:07 - recap: basics of the Interface 26:48 - Class Inheritance and Interface implementation 29:02 - Extracting the Interface from a Class 31:19 - Interface implementing another Interface 34:54 - Accessing a Class member outside the initial contract (Interface) in the List of type Interface 40:51 - Power of Interfaces: Adding a new Class to your project, why to use Interfaces