Reducing MVVM Light Viewmodel Code with Fody Property Dependencies and Custom Property Changed Methods

In other previous articles I’ve written about Fody and this article we’ll see how we can use the PropertyChanged.Fody addin with MVVM Light viewmodels.

Windows Store app screenshot

The preceding screenshot shows the app in action: a name TextBox is twoway data-bound to the viewmodel, when a different name is typed, the TextBlock shows the uppercase version.

The user can also type a color into the color box and a bit of reflection happens to convert this string to a color from the Colors class.

Windows Store app screenshot with different bg color

The following code shows the (non Fody-fied) viewmodel:

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Using the Xbox Music API in Universal Windows Apps

The Xbox Music API can be used by third party developers (i.e. you and me) to search for artists, songs, albums, etc and also get access to actually play songs.

There are two flavours at present: “unauthenticated” and “authenticated”.

Authenticated access allow playing of full songs and working with user playlists. Playlist changes will automatically roam to user’s other devices. The full access to play full songs requires that the user has an Xbox Music Pass.

Unauthenticated access doesn’t allow access to user playlists, and streaming of music is restrict to 30 second previews.

At present anyone can get unauthenticated access via the Xbox Music RESTful API on Azure Marketplace. Authenticated access is currently limited, you need to apply for the pilot program. I’ve applied for this, hopefully I’ll be accepted so I can understand this part better.

Getting Started with Unauthenticated Access

We need an access key to allow our apps to able to use the (unauthenticated) API. To do this follow these instructions to register and create an application in Azure Marketplace. Don’t worry about the code samples at the bottom of the post, there’s a client API we can use instead.

So now you should have an application registered (you might have to enter some web address in the redirect URI – I’m not sure what this is for at this point).

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Consuming Server-Side SignalR Events in Universal Windows App Clients

In a previous article I wrote about creating server side SignalR timer events.

As part of my learning of SignalR I wanted to see how easy it would be to create a Universal Windows app consuming these server side events.

So first off I created a new blank Universal app:

creating universal app in Visual Studio screenshot

 

Next installed the SignalR NuGet package into both app projects: install-package Microsoft.AspNet.SignalR.Client

In the Windows 8.1 Store app project XAML I added a simple bound TextBlock that will display the server messages:

<Page
    x:Class="UpTimeUni.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:UpTimeUni"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Viewbox>
            <TextBlock Text="{Binding Uptime}">please wait...</TextBlock>
        </Viewbox>
    </Grid>
</Page>

I also added similar XAML in the Windows Phone 8.1 main page.

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Using Server Side Timers and SignalR in ASP.NET MVC Applications

I thought it would be fun to create an “Internet uptime” page that you can see live here on Azure Websites. It shows how long the Internet (since ARPANET) has been around for.

image

Creating a Class that can be Managed by ASP.NET

The HostingEnvironment.RegisterObject method can be used to register an instance of an object that has its lifetime managed by the hosting environment.

To register an object it must implement the IRegisteredObject interface.

This interface defines a Stop method which gets called when ASP.NET needs to shutdown the app domain.

So, in the application start we can create an instance of our class and register it:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    RouteConfig.RegisterRoutes(RouteTable.Routes);

    HostingEnvironment.RegisterObject(new BackgroundUptimeServerTimer());
}

Creating a SignalR Hub to Send Messages from the Server to Client

Next we create a SignalR hub and the HTML.

So the hub class is called UptimeHub:

public class UptimeHub : Hub
{
}

We can get the server to call a client JavaScript method called “internetUpTime” in the HTML page and have this client code display the what’s been sent from the server timer.

The following shows the complete HTML for the page. Notice the “hub.client.internetUpTime = function (time) …” this function will get executed every time our server timer event fires.

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Say Goodbye to Boring INotifyPropertyChanged Implementation in Universal Windows Apps with Fody

We need to implement INotifyPropertyChanged to allow bindings to be updated. For example in a simple viewmodel to add 2 numbers:

namespace UniFodyDemo
{    
    internal class CalculatorViewModel : INotifyPropertyChanged
    {
        private ICommand _addCommand;
        private string _firstNumber;
        private string _secondNumber;

        public CalculatorViewModel()
        {
            FirstNumber = "5";
            SecondNumber = "10";
            Result = "";

            AddCommand = new RelayCommand(Add);
        }


        // Use strings to simplify demo code (so no val converter)
        public string FirstNumber
        {
            get { return _firstNumber; }
            set
            {
                _firstNumber = value;
                OnPropertyChanged();
            }
        }

        public string SecondNumber
        {
            get { return _secondNumber; }
            set
            {
                _secondNumber = value;
                OnPropertyChanged();
            }
        }

        public string Result { get; set; }

        public ICommand AddCommand
        {
            get { return _addCommand; }
            private set
            {
                _addCommand = value;
                OnPropertyChanged();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void Add(object obj)
        {
            var a = int.Parse(FirstNumber);
            var b = int.Parse(SecondNumber);

            Result = (a + b).ToString();
        }

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            var handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

There’s more code here than we’d need if we didn’t have to implement INotifyPropertyChanged. Really the important things are the 3 properties that we bind to and the add command / method.

The XAML in both the Windows Store app and Windows Phone app looks like:

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <StackPanel Width="200">
        <TextBlock Text="{Binding FirstNumber, Mode=TwoWay}"></TextBlock>
        <TextBlock Text="{Binding SecondNumber, Mode=TwoWay}"></TextBlock>
        <Button Command="{Binding AddCommand}">Add</Button>
        <TextBlock Text="{Binding Result, Mode=TwoWay}"></TextBlock>
    </StackPanel>
</Grid>

Without implementing INotifyProperty changed, clicking the Add button won’t be of much use, we wont see the result.

The solution looks like the following, the shared project contains the viewmodel.

image

It would be great not have to write this same INotifyProperty stuff for everything we want to bind to/from. Using a NuGet package called PropertyChanged.Fody we can achieve this.

First this package needs to be installed into both the Windows Store and Windows Phone app projects. This is because the shared code in the viewmodel isn’t compiled in that shared project, rather the source code is compiled individually in both the Store/Phone projects.

Now the viewmodel can be simplified:

namespace UniFodyDemo
{
    [ImplementPropertyChanged]
    class CalculatorViewModel
    {
        public CalculatorViewModel()
        {
            FirstNumber = "5";
            SecondNumber = "10";
            Result = "";

            AddCommand = new RelayCommand(Add);
        }

        private void Add(object obj)
        {
            var a = int.Parse(FirstNumber);
            var b = int.Parse(SecondNumber);

            Result = (a + b).ToString();
        }
        

        // Use strings to simplify demo code (so no val converter)
        public string FirstNumber { get; set; }
        public string SecondNumber { get; set; }
        public string Result { get; set; }

        public ICommand AddCommand { get; private set; }
    }
}

Notice the [ImplementPropertyChanged] attribute which means INotifyPropertyChanged will be automatically implemented for us. Notice that it’s much easier to see what’s essential in the viewmodel without all the noise of INotifyPropertyChanged.

If we decompile the Windows store app we can see the implementation:

namespace UniFodyDemo
{
    internal class CalculatorViewModel : INotifyPropertyChanged
    {
        public ICommand AddCommand
        {
            get
            {
                return this.u003cAddCommandu003ek__BackingField;
            }
            private set
            {
                if (this.u003cAddCommandu003ek__BackingField == value)
                {
                    return;
                }
                this.u003cAddCommandu003ek__BackingField = value;
                this.OnPropertyChanged("AddCommand");
            }
        }

        public string FirstNumber
        {
            get
            {
                return this.u003cFirstNumberu003ek__BackingField;
            }
            set
            {
                if (String.Equals(this.u003cFirstNumberu003ek__BackingField, value, 4))
                {
                    return;
                }
                this.u003cFirstNumberu003ek__BackingField = value;
                this.OnPropertyChanged("FirstNumber");
            }
        }

        public string Result
        {
            get
            {
                return this.u003cResultu003ek__BackingField;
            }
            set
            {
                if (String.Equals(this.u003cResultu003ek__BackingField, value, 4))
                {
                    return;
                }
                this.u003cResultu003ek__BackingField = value;
                this.OnPropertyChanged("Result");
            }
        }

        public string SecondNumber
        {
            get
            {
                return this.u003cSecondNumberu003ek__BackingField;
            }
            set
            {
                if (String.Equals(this.u003cSecondNumberu003ek__BackingField, value, 4))
                {
                    return;
                }
                this.u003cSecondNumberu003ek__BackingField = value;
                this.OnPropertyChanged("SecondNumber");
            }
        }

        public CalculatorViewModel()
        {
            this.FirstNumber = "5";
            this.SecondNumber = "10";
            this.Result = "";
            this.AddCommand = new RelayCommand(new Action<object>(this, CalculatorViewModel.Add));
        }

        private void Add(object obj)
        {
            int num = Int32.Parse(this.FirstNumber);
            int num1 = Int32.Parse(this.SecondNumber);
            this.Result = (num + num1).ToString();
        }

        public virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler propertyChangedEventHandler = this.PropertyChanged;
            if (propertyChangedEventHandler != null)
            {
                propertyChangedEventHandler(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
    }
}

So not only with Universal projects can we share code via the shared code project, adding Fody into the mix is even more awesome.

For a list of available addins or to contribute (or even create your own addin) check out the GitHub project site.

Also to learn more about Fody feel free to check out my Pluralsight course.

C# Tips eBook 50% Complete

I just published a new version of my C# Tips eBook that marks the half way point of the project.

C# Tips is available in PDF, EPUB, and MOBI.

The book is scheduled for completion by the end of the year and has 521 readers at present. It is currently free, you may also pay whatever you think it’s worth.

You can download it now from Leanpub.

An abridged copy of the current table of contents is shown below.

  • Merging IEnumerable Sequences with LINQ
  • Auto-Generating Sequences of Integer Values
  • Improving Struct Equality Performance
  • Creating Generic Methods in Non-Generic Classes
  • Converting Chars to Doubles
  • Non Short Circuiting Conditional Operators Using C# Keywords for Variable Names
  • Three Part Conditional Numeric Format Strings
  • Customizing the Appearance of Debug Information in Visual Studio
  • Partial Types
  • The Null Coalescing Operator
  • Creating and Using Bit Flag Enums
  • The Continue Statement
  • Preprocessor Directives
  • Automatically Stepping Through Code
  • Exceptions in Static Constructors
  • Safe Conversion To and From DateTime Strings
  • Parsing Strings into Numbers with NumberStyles
  • Useful LINQ Set Operations
  • The Decorator Pattern
  • The Factory Pattern
  • NUnit
  • xUnit.net

Write Less Repetitive Boilerplate Code with Fody

My newest Pluralsight course on Fody was just released.

Fody is a tool that frees us up from having to write repetitive boilerplate code. For example we can automate IDisposable implementation or automatically add Equals(), GetHashCode() and equality operators.

Fody is not one tool, but a collection of individual “addins” around the core Fody, with the core GitHub members: Simon Cropp, Rafał Jasica, and Cameron MacFarland.

Automatically Implementing Equality

As an example of what’s possible with Fody, we can auto-implement equality.

So first off we install the Equals Fody addin via NuGet:

PM> Install-Package Equals.Fody

Now we can add the [Equals] attribute to indicate that we want to auto-implement equality.

We can opt-out specific properties so they won’t be considered during equality by applying the [IgnoreDuringEquals] attribute.

We can also provide custom equality logic by creating a method and decorating it with the [CustomEqualsInternal] attribute. So for example if either altitude is –1 then consider altitudes equal.

The following code shows these attributes in action:

[Equals]
public class Location
{
    [IgnoreDuringEquals] 
    public int Altitude { get; set; }
    
    public int Lat { get; set; }
    public int Long { get; set; }

    [CustomEqualsInternal]
    private bool CustomEqualsLogic(Location other)
    {
        // this method is evaluated if the other auto-equal properties are equal

        if (this.Altitude == other.Altitude)
        {
            return true;
        }

        if (this.Altitude == -1 || other.Altitude == -1)
        {
            return true;
        }

        return false;
    } 
}

For a list of available addins or to contribute (or even create your own addin) check out the GitHub project site.

To learn more about how Fody works, how to use some of the available addins, and how to create your own check out my Pluralsight course.

Implementing Platform Specific Code in Universal Windows Apps with MVVMLight and Dependency Injection

In previous articles I’ve covered using MVVMLight in Universal Windows Apps and using C# partial classes and methods to implement different code on Windows Phone and Windows Store apps.

While partial classes/methods are a quick win to alter small amounts of code for each platform, overuse might become painful as the solution gets bigger. There are also limitations of partial methods such as they can only return void, they are implicitly private, cannot be virtual, etc.

If we’re using MVVMLight (or another framework or hand-rolled viewmodels) we can use dependency injection.

The viewmodel class is still shared between the two apps and doesn’t need to have partial methods which means we have more flexibility in the code we write.

As a dependency in the constructor, the viewmodel takes an instance of a class that implements an interface.

This interface-implementing class can then be two different classes, one in the phone project and one in the store project.

architecture diagram

So for example, in the shared project the following interface can be defined:

interface IGreetingService
{
    string GenerateGreeting();
}

Again in the shared project, the viewmodel is defined:

internal class MainViewModel : ViewModelBase
{
    private readonly IGreetingService _greetingService;
    private string _greeting;

    public MainViewModel(IGreetingService greetingService)
    {
        _greetingService = greetingService;

        SayHi = new RelayCommand(() => Greeting = _greetingService.GenerateGreeting());
    }

    public RelayCommand SayHi { get; set; }

    public string Greeting
    {
        get { return _greeting; }
        set { Set(() => Greeting, ref _greeting, value); }
    }
}

The key thing here is the constructor: it takes an IGreetingService.

When the SayHi command is executed, whichever instance of an IGreetingService was passed to the viewmodel, it’s GenerateGreeting() method will be called.

So in the store project the following class can be created:

public class WindowsStoreGreeter : IGreetingService
{
    public string GenerateGreeting()
    {
        return "Hello from Windows Store app!";
    }
}

And in the phone app:

public class WindowsPhoneGreeter : IGreetingService
{
    public string GenerateGreeting()
    {
        return "Hello from Windows Phone app!";
    }
}

It is in these specific implementations of the interface that the platform specific code is written.

So in the code-behind of the main window in the store app (for demonstration simplicity we’re not using a view model locator or DI library here):

public MainPage()
{
    this.InitializeComponent();

    this.DataContext = new MainViewModel(new WindowsStoreGreeter());
}

And in the phone app:

public MainPage()
{
    this.InitializeComponent();

    this.NavigationCacheMode = NavigationCacheMode.Required;

    this.DataContext = new MainViewModel(new WindowsPhoneGreeter());
}

In these code fragments a new MainViewModel is being created and supplied with a platform-specific IGreetingService implementation.

So in this way the shared MainViewModel class can still contain the majority of the code so we only have to write it once. But we still get the ability to write platform-specific code.

Using Shared Projects in Non-Universal App Projects

Using Visual Studio 2013 Update 2 and the Shared Project Manager Extension it’s possible to use shared projects in non Universal App projects.

This video shows a brief intro to shared projects in the context of Universal Apps and then how linked files work and how to refactor them to shared project.

As the documentation states: “Please note that this extension is preview technology and may have unforseen issues in the projects and solutions that it creates.”

Check out the video on YouTube or Vimeo.

Using MVVM Light in Universal Windows Apps

I though it would be interesting to see how easy it is to define an MVVM Light view model once and then use it in both a Universal Windows Phone and Windows Store project.

So I created a new blank universal apps project and added the “MVVM Light libraries only (PCL) NuGet” package to both the Windows 8.1 project and the Windows Phone 8.1 project.

Next create a new view model class in the shared project:

using System.Linq;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;

namespace UniMvvmLight
{
    class MainViewModel : ViewModelBase
    {
        public MainViewModel()
        {
            Words = "Hello";

            Reverse = new RelayCommand(() =>
                                       {
                                           Words = new string(Words.ToCharArray().Reverse().ToArray());
                                       });
        }

        private string _words;
        public RelayCommand Reverse { get; set; }

        public string Words
        {
            get
            {
                return _words;
            }
            set
            {
                Set(() => Words, ref _words, value);                
            }
        }
    }
}

I’m not going to create a view model locator etc, just simply set the datacontext in the code behind of both the phone and store MainWindow:

public MainPage()
{
    this.InitializeComponent();

    this.DataContext = new MainViewModel();
}

Next define the xaml in both the MainWindow.xaml in both phone and store projects:

<Grid>
    <StackPanel>
        <TextBox Text="{Binding Words}"></TextBox>
        <Button Command="{Binding Reverse}">Reverse</Button>
    </StackPanel>
</Grid>

Now running either the phone or store app works as expected, the view model binding works as expected and clicking the button reverses the string as expected. Whilst this is not surprising, the view model in the shared project is just like having a copy of it in both app projects, even so it’s still cool.

Windows phone simulator

If we wanted to we could then leverage C# partial classes and methods to define platform-specific viewmodel code.