Mastering Xamarin.Forms - Third Edition

By Ed Snider
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About 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.

Publication date:
December 2019
Publisher
Packt
Pages
200
ISBN
9781839213380

 

Getting Started

The goal of this book is to focus on how to apply best practices and patterns to mobile apps built with Xamarin.Forms, and not on the actual Xamarin.Forms toolkit and API itself. The best way to achieve this goal is to build an app end to end, applying new concepts in each chapter.

Therefore, the goal of this chapter is to simply put together the basic structure of a Xamarin.Forms mobile app code base, which will serve as a foundation that we can build from throughout the rest of this book.

In this chapter, we will do the following:

  • Introduce and define the features of the app that we will build throughout the rest of the book
  • Create a new Xamarin.Forms mobile app with an initial app structure and user interface

In the next chapter we'll introduce the Model-View-ViewModel (MVVM) pattern and add data bindings to the user interface we create in this chapter. From there we will build upon the app and its architecture, introducing best practices and patterns for things like platform-specific API dependencies, dependency injection, remote data access, authentication, and unit testing. But, just like the beginning of many new mobile projects, we will start with an idea.

 

Introducing the app idea

We will create a travel app named TripLog and, as the name suggests, it will be an app that will allow its users to log their travel adventures. Although the app itself will not solve any real-world problems, it will have features that will require us to solve real-world architecture and coding problems. The app will take advantage of several core concepts, such as list views, maps, location services, and live data from a RESTful API, and we will apply patterns and best practices throughout this book to implement these concepts.

Defining features

Before we get started, it is important to understand the requirements and features of the TripLog app. We will do this by quickly defining some of the high-level things this app will allow its users to do:

  • View existing log entries (online and offline)
  • Add new log entries with the following data:
    • Title
    • Location using GPS
    • Date
    • Notes
    • Rating
  • Sign into the app

The following screenshots show some of the iOS and Android screens of the app we will be creating. The first screenshot shows the initial screen running on iOS with the list of all the user's trip log entries. The middle screenshot shows the trip log detail screen using native maps. The last screenshot shows the screen that lets users add new trip log entries running on Android:

Figure 1: The TripLog app as it will appear at the end of the book

 

Creating the initial app

To start off the new TripLog mobile app project, we will need to create the initial solution architecture. We can also create the core shell of our app's user interface by creating the initial screens based on the basic features we have just defined.

Setting up the solution

We will start things off by creating a brand new, blank Xamarin.Forms solution within Visual Studio by performing the following steps:

  1. In Visual Studio, click on File | New Solution. This will bring up a series of dialog screens that will walk you through creating a new Xamarin.Forms solution. On the first dialog, click on App on the left-hand side, under the Multiplatform section, and then select Blank Forms App, as shown in the following screenshot:

    Figure 2: Xamarin.Forms new project setup in Visual Studio (step 1 of 3)

  2. On the next dialog screen, enter the name of the app, TripLog, and ensure that Use .NET Standard is selected for the Shared Code option, as shown in the following screenshot:

    You can use either .NET Standard or a Shared Library for the code sharing option when creating a new Xamarin.Forms project. There are benefits to both but we will use .NET Standard, as it lends itself better to the architecture patterns and testability objectives of this book.

    Figure 3: Xamarin.Forms new project setup in Visual Studio (step 2 of 3)

  3. On the final dialog screen, simply click on the Create button, as follows:

    Figure 4: Xamarin.Forms new project setup in Visual Studio (step 3 of 3)

  4. After creating the new Xamarin.Forms solution, you will have several projects created within it, as shown in the following screenshot:

Figure 5: The TripLog solution in Visual Studio

There will be a single .NET Standard project and two platform-specific projects, as follows:

  • TripLog: This is a .NET Standard project that will serve as the core layer of the solution architecture. This is the layer that will include all our business logic, data objects, Xamarin.Forms pages, and other non-platform-specific code. The code in this project is common and not specific to a platform, and can therefore be shared across the platform projects.
  • TripLog.iOS: This is the iOS platform-specific project containing all the code and assets required to build and deploy the iOS app from this solution. By default, it will have a reference to the TripLog core project.
  • TripLog.Android: This is the Android platform-specific project containing all the code and assets required to build and deploy the Android app from this solution. By default, it will have a reference to the TripLog core project.

If you are using Visual Studio for Mac, you will only get an iOS and an Android project when you create a new Xamarin.Forms solution. To include a Windows (UWP) app in your Xamarin.Forms solution, you will need to use Visual Studio for Windows. Although the screenshots and samples used throughout this book are demonstrated using Visual Studio for Mac, the code and concepts will also work in Visual Studio for Windows. Refer to the Preface of this book for further details on software and hardware requirements that need to be met to follow along with the concepts in this book.

You'll notice a file in the core library named App.xaml, which includes a code-behind class in App.xaml.cs named App that inherits from Xamarin.Forms.Application. Initially, the App constructor sets the MainPage property to a new instance of a ContentPage named MainPage that simply displays some default text.

The first thing we will do in our TripLog app is build the initial views, or screens, required for our UI, and then update that MainPage property of the App class in App.xaml.cs.

Updating the Xamarin.Forms packages

If you expand the Dependencies > NuGet folder within the main TripLog project, and the Packages folder in each of the platform projects in the solution, you will see that Xamarin.Forms is a NuGet package that is automatically included when we select the Xamarin.Forms project template. It is possible that the included NuGet packages need to be updated. Update the Xamarin.Forms NuGet packages in each of the projects within the solution to the latest version available.

New for Third Edition!

In this edition of Mastering Xamarin.Forms we will take advantage of some of the new features and capabilities of Xamarin.Forms 4. To do this, we will require a minimum stable version of 4.3 of the Xamarin.Forms NuGet package.

Creating the main page

The main page of the app will serve as the entry point into the app and will display a list of existing trip log entries. Our trip log entries will be represented by a data model named TripLogEntry. Models are a key pillar in the MVVM pattern and data binding, which we will explore more in Chapter 2, MVVM and Data Binding; however, in this chapter, we will create a simple class that will represent the TripLogEntry model.

Let's now start creating the main page by performing the following steps:

  1. First, delete the default MainPage.xaml and its code-behind file, MainPage.xaml.cs, from the TripLog project. We will create our own MainPage.
  2. Next, add a new folder named Views to the root of the TripLog project. This folder will be where app pages in the application live.
  3. Next, add a new Xamarin.Forms XAML ContentPage to the Views folder in the TripLog project and name it MainPage.
  4. Next, update the MainPage property of the App class in App.xaml.cs to a new instance of Xamarin.Forms.NavigationPage whose root is a new instance of TripLog.MainPage that we just created:
    using Xamarin.Forms;
    using TripLog.Views;
    namespace TripLog
    {
        public partial class App : Application
        {
            public App()
            {
                InitializeComponent();
                MainPage = new NavigationPage(new MainPage());
            }
            // ...
        }
    }
    

    Notice how we are wrapping our MainPage with a NavigationPage. By doing this, we automatically get native components for navigating between pages.

  5. Create a new folder in the TripLog project named Models.
  6. Create a new empty class file in the Models folder named TripLogEntry.
  7. Update the TripLogEntry class with auto-implemented properties representing the attributes of an entry:
    public class TripLogEntry
    {
        public string Title { get; set; } 
        public double Latitude { get; set; } 
        public double Longitude { get; set; } 
        public DateTime Date { get; set; } 
        public int Rating { get; set; } 
        public string Notes { get; set; }
    }
    
  8. Now that we have a model to represent our trip log entries, we can use it to display some trips on the main page using a CollectionView control. We will use a DataTemplate to describe how the model data should be displayed in each of the rows in the CollectionView using the following XAML in the ContentPage.Content tag in MainPage.xaml:
    <ContentPage 
        xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        x:Class="TripLog.Views.MainPage"
        Title="TripLog">
        <ContentPage.Content>
            <CollectionView x:Name="trips"
                SelectionMode="Single">
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                        <Grid Padding="10">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="1*" />
                                <ColumnDefinition Width="3*" />
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto" />
                                <RowDefinition Height="Auto" />
                            </Grid.RowDefinitions>
                            <Label Grid.RowSpan="2"
                                   Text="{Binding Date, StringFormat='{0:MMM d}'}" />
                            <Label Grid.Column="1"
                                   Text="{Binding Title}"
                                   FontAttributes="Bold" />
                            <Label Grid.Column="1"
                                   Grid.Row="1"
                                   Text="{Binding Notes}" />
                        </Grid>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
            </CollectionView>
        </ContentPage.Content>
    </ContentPage>
    
  9. In the main page's code-behind, MainPage.xaml.cs, we will populate the CollectionView ItemsSource with a hardcoded collection of TripLogEntry objects. In the next chapter, we will move this collection to the page's data context (that is, its ViewModel), and in Chapter 6, API Data Access, we will replace this hardcoded data with data from a live Azure backend:
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
            var items = new List<TripLogEntry>
            {
                new TripLogEntry
                {
                    Title = "Washington Monument", 
                    Notes = "Amazing!",
                    Rating = 3,
                    Date = new DateTime(2019, 2, 5),
                    Latitude = 38.8895,
                    Longitude = -77.0352
                },
                new TripLogEntry
                {
                    Title = "Statue of Liberty", 
                    Notes = "Inspiring!",
                    Rating = 4,
                    Date = new DateTime(2019, 4, 13),
                    Latitude = 40.6892,
                    Longitude = -74.0444
                },
                new TripLogEntry
                {
                    Title = "Golden Gate Bridge", 
                    Notes = "Foggy, but beautiful.", 
                    Rating = 5,
                    Date = new DateTime(2019, 4, 26),
                    Latitude = 37.8268,
                    Longitude = -122.4798
                }
            };
            trips.ItemsSource = items;
        }
    }
    

At this point, we have a single page that is displayed as the app's main page. If we debug the app and run it in a simulator, emulator, or on a physical device, we should see the main page showing the list of log entries we hardcoded into the view, as shown in the following screenshot:

Figure 6: The TripLog main page

In Chapter 2, MVVM and Data Binding, we will refactor this quite a bit as we implement MVVM and leverage the benefits of data binding.

Creating the new entry page

The new entry page of the app will give the user a way to add a new log entry by presenting a series of fields to collect the log entry details. There are several ways to build a form to collect data in Xamarin.Forms. You can simply use a StackLayout and present a stack of Label and Entry controls on the screen, or you can also use a TableView with various types of ViewCell elements. In most cases, a TableView will give you a very nice default, platform-specific look and feel. However, if your design calls for a more customized aesthetic, you might be better off leveraging the other layout options available in Xamarin.Forms. For the purpose of this app, we will use a TableView.

There are some key data points we need to collect when our users log new entries with the app, such as title, location, date, rating, and notes. For now, we will use a regular EntryCell element for each of these fields. We will update, customize, and add things to these fields later in this book. For example, we will wire the location fields to a geolocation service that will automatically determine the location. We will also update the date field to use an actual platform-specific date picker control. For now, we will just focus on building the basic app shell.

In order to create the new entry page that contains a TableView, perform the following steps:

  1. First, add a new Xamarin.Forms XAML ContentPage to the Views folder in the TripLog project and name it NewEntryPage.
  2. Update the new entry page using the following XAML to build the TableView that will represent the data entry form on the page:
    <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        x:Class="TripLog.Views.NewEntryPage"
        Title="New Entry">
        <ContentPage.Content>
            <TableView Intent="Form">
                <TableView.Root>
                    <TableSection>
                        <EntryCell Label="Title" />
                        <EntryCell Label="Latitude"
                            Keyboard="Numeric" />
                        <EntryCell Label="Longitude"
                            Keyboard="Numeric" />
                        <EntryCell Label="Date" />
                        <EntryCell Label="Rating"
                            Keyboard="Numeric" />
                        <EntryCell Label="Notes" />
                    </TableSection>
                </TableView.Root>
            </TableView>
        </ContentPage.Content>
    </ContentPage>
    

Now that we have created the new entry page, we need to add a way for users to get to this new screen from the main page. We will do this by adding a New button to the main page's toolbar. In Xamarin.Forms, this is accomplished by adding a ToolbarItem to the ContentPage.ToolbarItems collection and wiring up the ToolbarItem.Clicked event to navigate to the new entry page, as shown in the following XAML:

<!-- MainPage.xaml -->
<ContentPage
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    x:Class="TripLog.Views.MainPage"
    Title="TripLog">
    <ContentPage.ToolbarItems>
        <ToolbarItem Text="New" Clicked="New_Clicked" />
    </ContentPage.ToolbarItems>
    <ContentPage.Content>
        <!-- ... -->
    </ContentPage.Content>
</ContentPage>
// MainPage.xaml.cs
public partial class MainPage : ContentPage
{
    // ...
    void New_Clicked(object sender, EventArgs e)
    {
        Navigation.PushAsync(new NewEntryPage());
    }
}

In Chapter 3, Navigation, we will build a custom service to handle navigation between pages and will replace the Clicked event with a data-bound ICommand ViewModel property, but for now, we will use the default Xamarin.Forms navigation mechanism.

When we run the app, we will see a New button on the toolbar of the main page. Clicking on the New button should bring us to the new entry page, as shown in the following screenshot:

Figure 7: The TripLog new entry page

We will need to add a save button to the new entry page toolbar so that we can save new items. For now, this button will just be a placeholder in the UI that we will bind an ICommand to in Chapter 2, MVVM and Data Binding. The save button will be added to the new entry page toolbar in the same way the New button was added to the main page toolbar. Update the XAML in NewEntryPage.xaml to include a new ToolbarItem, as shown in the following code:

<ContentPage>
    <ContentPage.ToolbarItems>
        <ToolbarItem Text="Save" />
    </ContentPage.ToolbarItems>
    
    <!-- ... -->
</ContentPage>

When we run the app again and navigate to the new entry page, we should now see the Save button on the toolbar, as shown in the following screenshot:

Figure 8: The TripLog new entry page with Save button

Creating the entry detail page

When a user clicks on one of the log entry items on the main page, we want to take them to a page that displays more details about that particular item, including a map that plots the item's location. Along with additional details and a more in-depth view of the item, a detail page is also a common area where actions on that item might take place, such as editing the item or sharing the item on social media. The detail page will take an instance of a TripLogEntry model as a constructor parameter, which we will use in the rest of the page to display the entry details to the user.

In order to create the entry detail page, perform the following steps:

  1. First, add a new Xamarin.Forms XAML ContentPage to the Views folder in the TripLog project and name it DetailPage.
  2. Update the constructor of the DetailPage class in DetailPage.xaml.cs to take a TripLogEntry parameter named entry, as shown in the following code:
    using Xamarin.Forms;
    using TripLog.Models;
    // ...
    public partial class DetailPage : ContentPage
    {
        public DetailPage(TripLogEntry entry)
        {
            // ...
        }
    }
    
  3. Add the Xamarin.Forms.Maps NuGet package to the core TripLog project and to each of the platform-specific projects. This separate NuGet package is required in order to use the Xamarin.Forms Map control in the next step.
  4. Update the XAML in DetailPage.xaml to include a Grid layout to display a Map control and some Label controls to display the trip's details, as shown in the following code:
    <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        xmlns:maps="clr-namespace:Xamarin.Forms.Maps;assembly=Xamarin.Forms.Maps"
        x:Class="TripLog.Views.DetailPage">
        <ContentPage.Content>
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="4*" />
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="1*" />
                </Grid.RowDefinitions>
                <maps:Map x:Name="map" Grid.RowSpan="3" />
                <BoxView Grid.Row="1" BackgroundColor="White"
                    Opacity=".8" />
                <StackLayout Padding="10" Grid.Row="1">
                    <Label x:Name="title"
                        HorizontalOptions="Center" />
                    <Label x:Name="date"
                        HorizontalOptions="Center" />
                    <Label x:Name="rating"
                        HorizontalOptions="Center" />
                    <Label x:Name="notes"
                        HorizontalOptions="Center" />
                </StackLayout>
            </Grid>
        </ContentPage.Content>
    </ContentPage>
    
  5. Update the detail page's code-behind, DetailPage.xaml.cs, to center the map and plot the trip's location. We also need to update the Label controls on the detail page with the properties of the entry constructor parameter:
    using Xamarin.Forms;
    using Xamarin.Forms.Maps;
    using TripLog.Models;
    
    // ...
    public DetailPage(TripLogEntry entry)
    {
        InitializeComponent();
        map.MoveToRegion(MapSpan.FromCenterAndRadius(
            new Position(entry.Latitude, 
                entry.Longitude),
                Distance.FromMiles(.5)));
        map.Pins.Add(new Pin
        {
            Type = PinType.Place, 
            Label = entry.Title,
            Position = new Position(entry.Latitude, entry.Longitude)
        });
        title.Text = entry.Title;
        date.Text = entry.Date.ToString("M");
        rating.Text = $"{entry.Rating} star rating";
        notes.Text = entry.Notes;
    }
    
  6. Next, we need to wire up the ItemTapped event of the CollectionView on the main page to pass the tapped item over to the entry detail page that we have just created, as shown in the following code:
    <!-- MainPage.xaml -->
    <CollectionView x:Name="trips"
        SelectionMode="Single"
        SelectionChanged="Trips_SelectionChanged">
        <!-- ... -->
    </CollectionView>
    // MainPage.xaml.cs 
    public partial class MainPage : ContentPage
    {
        // ...
        async void Trips_SelectionChanged(object s, SelectionChangedEventArgs e)
        {
            var trip = (TripLogEntry)e.CurrentSelection.FirstOrDefault();
            if (trip != null)
            {
                await Navigation.PushAsync(new DetailPage(trip));
            }
            // Clear selection 
            trips.SelectedItem = null;
        }
    }
    
  7. Next, add your Google Maps API Key to the AndroidManifest.xml file in the Android project:
    <application android:label="TripLog.Android">
        <meta-data 
            android:name="com.google.android.maps.v2.API_KEY"
            android:value="YOUR-MAPS-API-KEY-HERE" />
    </application>
    

    There are some additional steps required for Google Maps to work in the Android app. You can read more about how to properly set everything up in the Xamarin.Forms Map documentation at https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/map.

  8. Finally, we will need to initialize the Xamarin.Forms.Maps library in each platform-specific startup class (AppDelegate for iOS and MainActivity for Android) using the following code:
    // in iOS AppDelegate 
    global::Xamarin.Forms.Forms.Init(); 
    Xamarin.FormsMaps.Init(); 
    LoadApplication(new App());
    // in Android MainActivity 
    global::Xamarin.Forms.Forms.Init(this, savedInstanceState); 
    Xamarin.FormsMaps.Init(this, savedInstanceState); 
    LoadApplication(new App());
    

Now, when we run the app and tap on one of the log entries on the main page, it will navigate us to the details page to see more detail about that particular log entry, as shown in the following screenshot:

Figure 9: The TripLog entry detail page

 

Summary

In this chapter, we built a simple three-page app with static data, leveraging the most basic concepts of the Xamarin.Forms toolkit. We used the default Xamarin.Forms navigation APIs to move between the three pages, which we will refactor in Chapter 3, Navigation, to use a more flexible, custom navigation approach.

Now that we have built the foundation of the app, including the basic UI for each page within the app, we'll begin enhancing the app with better architecture design patterns, live data with offline syncing, nicer looking UI elements, and tests. In the next chapter, we will introduce the MVVM pattern and data binding to the app to enforce a separation between the user interface layer and the business and data access logic.

About the Author

  • Ed Snider

    Ed Snider is a senior software developer, speaker, author, and Microsoft MVP based in the Washington D.C./Northern Virginia area. He has a passion for mobile design and development and regularly speaks about Xamarin and Windows app development in the community. Ed works at InfernoRed Technology, where his primary role is working with clients and partners to build mobile products on iOS, Android, and Windows. He's been coding for over half of his life, starting out by working part time in high school updating the local newspaper's website and building web apps for small businesses in his hometown. Ed started working with the .NET in 2005 and has been building mobile apps with .NET since 2011. Ed was recognized as a Xamarin MVP in 2015 and as a Microsoft MVP in 2017.

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