The Polly documentation has a great explanation of the circuit-breaker pattern  

Cards...or indeed any XAML content can easily be flipped using the new Flipper control and MaterialDesignCardFlipper style. 

Singleton design pattern is one of the simplest design patterns: it involves only one class throughout the application which is responsible to instantiate itself, to make sure it creates not more than one instance; in the same time it provides a global point of access to that instance. In this case the same instance can be used from everywhere, being impossible to invoke directly the constructor each time. 

In this series, we're going to walk through the database design of our Workflow app and show each part of the solution was implemented, and finally how they were all wired together 

How you shouldn’t implement base classes

public class Entity<T>
{

  public T Id { get; protected set; }

}

Motivation for such code it pretty clear: you have a base class that can be reused across multiple projects. For instance, if there is a web application with GUID Id columns in the database and a desktop app with integer Ids, it might seem a good idea to have the same class for both of them. In fact, this approach introduces accidental complexity because of premature generalization. 

There is no need in using a single base entity class for more than one project or bounded context. Each domain has its unique path, so let it grow independently. Just copy and paste the base entity class to a new project and specify the exact type that will be used for the Id property. 

SOLID Design Patterns