Book Image

Mastering Xamarin.Forms - Third Edition

By : Ed Snider
Book Image

Mastering Xamarin.Forms - Third Edition

By: Ed Snider

Overview of this book

Discover how to extend and build upon the components of the most recent version of Xamarin.Forms to develop an effective, robust mobile app architecture. This new edition features Xamarin.Forms 4 updates, including CollectionView and RefreshView, new coverage of client-side validation, and updates on how to implement user authentication. Mastering Xamarin.Forms, Third Edition is one of the few Xamarin books structured around the development of a simple app from start to finish, beginning with a basic Xamarin.Forms app and going step by step through several advanced topics to create a solution architecture rich with the benefits of good design patterns and best practices. This book introduces a core separation between the app's user interface and the app's business logic by applying the MVVM pattern and data binding, and then focuses on building a layer of plugin-like services that handle platform-specific utilities such as navigation and geo-location, as well as how to loosely use these services in the app with inversion of control and dependency injection. You’ll connect the app to a live web-based API and set up offline synchronization before testing the app logic through unit testing. Finally, you will learn how to add monitoring to your Xamarin.Forms projects to track crashes and analytics and gain a proactive edge on quality.
Table of Contents (12 chapters)

Adding a sign-in page

In order to add sign-in capabilities to our app, we need to create a new Page and a new ViewModel. The ViewModel will be pretty straightforward, containing just a single command that handles signing into Facebook via the IAuthService interface, and passing the received Facebook token to the Azure backend service through the ITripLogDataService, as shown in the following steps:

  1. Create a new class that inherits from BaseViewModel, named SignInViewModel, in the ViewModels folder in the core library project:
    public class SignInViewModel : BaseViewModel
    {
    }
    
  2. Update the SignInViewModel with a constructor that takes in INavService, IAuthService, and ITripLogDataService parameters:
    public class SignInViewModel : BaseViewModel
    {
        readonly IAuthService _authService;
        readonly ITripLogDataService _tripLogService;
        public SignInViewModel(INavService navService, 
            IAuthService authService, 
            ITripLogDataService tripLogService)
            :base...