Since we have a good idea of what the application is, the next step is to develop the business objects, or Model layer, of this application. Let's start by defining a few classes that will contain the data to be used throughout the app. It is recommended, for the sake of organization, to add these to a Models folder in your project. This is the bottom layer of the MVVM design pattern.

Let's begin with a class that represents a user. The class can be created as follows:

public class User
{
  public string Id { get; set; }
  public string Username { get; set; }
  public string Password { get; set; }
}

Pretty straightforward so far; let's move on to create classes representing a conversation and a message as follows:

public class Conversation
{
  public string Id { get; set; }
  public string UserId { get; set; } 
  public string Username { get; set; }
}
public class Message
{
  public string Id { get; set; }
  public string ConversationId { get; set; }
  public string UserId { get; set; } 
  public string Username { get; set; }
  public string Text { get; set; }
}

Notice that we are using strings as identifiers for the various objects. This will simplify our integration with Azure Mobile Services in the later chapters. UserId is the value that will be set by the application to change the user that the object is associated with.

Now, let's go ahead and set up our solution by performing the following steps: