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Mastering Xamarin.Forms
Mastering Xamarin.Forms

Mastering Xamarin.Forms: App architecture techniques for building multi-platform, native mobile apps with Xamarin.Forms 4 , Third Edition

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Mastering Xamarin.Forms

MVVM and Data Binding

In this chapter, we will take a look at the Model-View-ViewModel (MVVM) pattern, the MVVM elements that are offered with the Xamarin.Forms toolkit, and how we can expand on them to truly take advantage of the power of the pattern. As we dig into these topics, we will apply what we have learned to the TripLog app that we started building in Chapter 1, Getting Started.

In this chapter, we will cover the following topics:

  • Understanding the MVVM pattern and data binding
  • Adding the MVVM pattern and data binding to the Xamarin.Forms mobile app created in Chapter 1, Getting Started
  • Adding client-side validation to the Xamarin.Forms mobile app created in Chapter 1, Getting Started

Before we start applying the MVVM pattern to our app we will review the basics of the pattern in the following section.

Understanding the MVVM pattern

At its core, MVVM is a presentation pattern designed to control the separation between user interfaces and the rest of an application. The key elements of the MVVM pattern are as follows:

  • Models: Models represent the business entities of an application. When responses come back from an API, they are typically deserialized to Models.
  • Views: Views represent the actual pages or screens of an application, along with all of the elements that make them up, including custom controls. Views are very platform-specific and depend heavily on platform APIs to render the application's user interface (UI).
  • ViewModels: ViewModels control and manipulate the Views by serving as their data context. ViewModels are made up of a series of properties represented by Models. These properties are part of what is bound to the Views to provide the data that is displayed to users, or to collect the data that is entered or selected by users. In addition to Model...

Adding MVVM to the app

The first step of introducing MVVM into an app is to set up the structure by adding folders that will represent the core tenants of the pattern, such as Models, ViewModels, and Views. Traditionally, the Models and ViewModels live in a core library (usually, a portable class library or .NET standard library), whereas the Views live in a platform-specific library.

Thanks to the power of the Xamarin.Forms toolkit and its abstraction of platform-specific UI APIs, the Views in a Xamarin.Forms app can also live in the core library.

Just because the Views can live in the core library with the ViewModels and Models doesn't mean that separation between the UI and the app logic isn't important. As we will see in this chapter and throughout the rest of the book, the separation between the UI and app logic is instrumental in keeping the codebase maintainable, testable, and shareable.

When implementing a specific structure to support...

Validation

In software, data validation is a process that ensures the validity and integrity of user input and usually involves checking that data is in the correct format and contains an acceptable value. There are typically two types of validation when building apps: server-side and client-side. Both play an important role in the lifecycle of an app's data. Server-side validation is critical when it comes to security, making sure malicious data or code doesn't make its way into the server or backend infrastructure. Client-side validation is usually more about user experience than security. A mobile app should always validate its data before sending it to a backend (such as a web API) for a number of reasons, including the following:

  • To provide real-time feedback to the user about any issues instead of waiting on a response from the backend
  • To support saving data in offline scenarios where the backend is not available
  • To prevent encoding issues when sending...

Summary

In this chapter, we updated the app that we started creating in Chapter 1, Getting Started, by removing data and data-related logic from the Pages, offloading it to a series of ViewModels, and then binding the Pages to those ViewModels. In the next chapter, we will expand on the Xamarin.Forms navigation service so that we can also move navigation code from the Pages to the ViewModels.

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Key benefits

  • Updated for Xamarin.Forms 4
  • Packed with real-world scenarios and solutions to help you build professional grade mobile apps with Xamarin.Forms
  • Includes design patterns and best practice techniques that every mobile developer should know

Description

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.

Who is this book for?

This book is intended for .NET developers who are familiar with Xamarin mobile application development and the open source Xamarin.Forms toolkit. If you have already started working with Xamarin.Forms and want to take your app to the next level, making it more maintainable, testable and flexible, then this book is for you.

What you will learn

  • Find out how, when, and why to use architecture patterns and best practices with Xamarin.Forms
  • Implement the Model-View-ViewModel (MVVM) pattern and data binding in Xamarin.Forms mobile apps
  • Incorporate client-side validation in Xamarin.Forms mobile apps
  • Extend the Xamarin.Forms navigation API with a custom ViewModel-centric navigation service
  • Leverage the inversion of control and dependency injection patterns in Xamarin.Forms mobile apps
  • Work with online and offline data in Xamarin.Forms mobile apps
  • Use platform-specific APIs to build rich custom user interfaces in Xamarin.Forms mobile apps
  • Explore how to monitor mobile app quality using Visual Studio App Center
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Publication date, Length, Edition, Language, ISBN-13
Publication date : Dec 30, 2019
Length: 200 pages
Edition : 3rd
Language : English
ISBN-13 : 9781839213380
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Publication date : Dec 30, 2019
Length: 200 pages
Edition : 3rd
Language : English
ISBN-13 : 9781839213380
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Table of Contents

11 Chapters
Getting Started Chevron down icon Chevron up icon
MVVM and Data Binding Chevron down icon Chevron up icon
Navigation Chevron down icon Chevron up icon
Platform-Specific Services and Dependency Injection Chevron down icon Chevron up icon
User Interface Chevron down icon Chevron up icon
API Data Access Chevron down icon Chevron up icon
Authentication Chevron down icon Chevron up icon
Testing Chevron down icon Chevron up icon
App Monitoring Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

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xmichael Sep 24, 2021
Full star icon Empty star icon Empty star icon Empty star icon Empty star icon 1
This book is very short and super basic. Almost 1/2 the book is about setting up Azur, and a good 20% is just filler content, 1/2 a page is dedicated to name tools that you can use to expand a zip file. What a joke.
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Nadine Meißner Apr 19, 2021
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Wurde verschenkt. Dem beschenkten gefiel es Sehr.
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Amazon Customer Jan 23, 2021
Full star icon Empty star icon Empty star icon Empty star icon Empty star icon 1
I am trying to learn Xamarin Forms and gave this book a try. Well after having error message and spending weeks and weeks of googling with no results I finally got in touch with the author. He would not respond to the tweets that I sent him so i seen he works with another company. I Tweet them and next thing you know Ed got back with me. I explained to him the issue I was having and he requested pictures and section i was having issues with. I sent screenshots and a text letter explaining area of the book errors where occurring. He never got back with me and after several weeks of googling and posting to several Facebook groups i was able to find the answer. I found out a lot of people was having the same issue. Finally Ed got back with and I gave him the results of my research and a new error i found in his book. He never emailed back to help or even to thank me for helping him when he doesn't care to help me. VERY AWFUL AUTHOR.
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Gunter R. Beck Sep 14, 2020
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The book is page after page actual working samples and examples. You may skip a chapter, say on Dependency Services; but you will always have a working app. Great as a reference app on your 'backup' drive. I highly recommend Ed Snider
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Timbo Aug 27, 2020
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This book is very good about build MVVM apps using Xamarin. While it is written for VS Mac, it will work with VS Windows.One of things about Xamarin is that like Java, there is a lot of coding you see in the examples that doesn't make a lot of sense right away. The book tells you what is does but I wish they were better with comments in the examples. If you're going to use the books examples for coding purposes in the future, its a good idea to connect the dots.I wish this book covered editing data in a table. A lot of Xamarin books that I have seen do a poor job of that. I'm only halfway through the book and looked ahead and didn't see any examples in here.
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