Microsoft and Xamarin, Google and Swift

Xamarin

A few months ago I was looking at mobile app development again and so had a look at Xamarin, a cross-platform app toolset built around .NET. It seemed interesting, but it was hugely expensive. Something like $600 per year per license. When Android Studio is free and XCode is either free or $99, it was cheaper to go native.

Microsoft Buys Xamarin

Now Microsoft has acquired Xamarin and it will be free to use. So now you can theoretically write C# code and have it build (with some additional platform-specific effort) Android and iOS (and Windows Phone, if anyone cares) apps cheaply.

Google needs a new first-class language… Swift?

With Oracle constantly trying to squeeze money out of Google for their use of Java on Android, Google very obviously needs a new first-class language for Android – one that can eventually replace Java completely. Reportedly they’re considering using Apple’s Swift. Although I’ve spent only a little time with Swift, it seems like an excellent language. Like F#, it’s a hybrid functional language with objects.

Write once… in C# or Swift?

Xamarin’s supposed advantage is that you can write in one language, C#, and compile to iOS or Android. What if Swift becomes the native language for both platforms? Someone will create libraries to cross-compile the UI elements. What need is there then for Xamarin? Swift is a more modern language. Though Xamarin theoretically supports all .NET languages and thus would support F#, we know F# is a second-class citizen. Xamarin would be solely for those .NET developers who are unable to move on to new languages. If Google does adopt Swift for Android, Xamarin will become the mobile equivalent of WebForms.

Visual Studio Code Coverage: Value does not fall within the expected range

While attempting to improve my code coverage in Visual Studio 2014, I suddenly found myself getting the error “Value does not fall within the expected range” when running unit tests with code coverage enabled. Without code coverage, the tests ran fine. With code coverage, that error would appear twice in the test output.

I googled the error for awhile and mostly came up empty. I eventually tracked down this post where a user was getting the same message but related to website profiling. It did help me track down the issue though.

The solution

I looked in the configuration manager. It turns out that while most of the projects in my solution were set to the “Any CPU” platform, I had one Wix installer project set to “x86”, presumably because it’s building an x86-compatible installer. If this project is disabled, code coverage works. If re-enabled, I get the error. For now, I’ve just been disabling the program when I want to do code coverage.

Akka.NET, Prism, Unity, and WPF

Since I’ve been reading up on Reactive Extensions, I listened with interest to the recent .NET Rocks! podcast on the subject. During the conversation, Akka.NET was mentioned.

Akka.NET is another reactive technology. It’s an implementation of the Actor model. Basically, you break down an application’s functionality into small computational units called Actors which have limited state and communicate via message passing. There are parallels in Rx’s concept of observables and observers. Akka.NET also provides the kind of supervision hierarchy that you find in erlang, which is that an actor has child actors and when those child actors fail, the parent can resume or restart the failed children. This makes the application ‘self healing’.

I watched two Pluralsight course on Akka.NET by Jason Roberts, Building Concurrent Applications with the Actor Model in Akka.NET and Building Reactive Concurrent WPF Applications with Akka.NET (subscriptions required for both links). The former gives an overview of Akka.NET and the latter applies it to an MVVM WPF application.

In the demo MVVM application, the author uses Akka.NET with Ninject dependency injection and the MVVM Light toolkit. Personally, I prefer Unity and Prism, so as an exercise for myself I created the demo using those two languages. The result is on GitHub at https://github.com/mkb137/AkkaPrismUnityDemo.

The project consists of
* Akka.DI.Unity – A copy of Akka.NET’s Akka.DI.Unity upgraded from Unity 3.5 to Unity 4.0. No code changes were required otherwise.
* AkkaPrismUnityDemo – The Prism shell project
* AkkaPrismUnityDemo.Infrastructure – The common infrastructure project (which in this simple demo only contains the region names)
* AkkaPrismUnityDemo.Modules.Stocks – The main module containing the demo code.

A screenshot of the result is shown at the top of this post. In it, the view model creates actors which then have knowledge of the view model that created them and will call methods on the view model when messages are received and processed.

Here a view model creates an actor and passes it a reference to itself:

this.StockToggleButtonActorRef = 
    this.UnityContainer.Resolve<ActorSystem>()
    .ActorOf( 
        Props.Create( () => new StockToggleButtonActor( 
            this.StocksCoordinatorActorRef, 
            this, 
            this.StockSymbol
        ) 
    ) 
);

Here the actor makes a callback to the view model:

this.Receive<ToggleStockMessage>( message => {
    this._stocksCoordinatorActorRef.Tell( new WatchStockMessage( this._stockSymbol ) );
    this._viewModel.UpdateButtonTextToOn();
    this.Become( this.ToggledOn );
} );

Like Rx and its Observables/Observers, messages are handled on the thread pool so actors will make full use of the processors available on the machine with no extra effort from the developer.

It’s an interesting technology. Compared to Rx, Akka is missing some of Rx’s advanced publish/subscribe methods like the ability to buffer or throttle messages. It does have a Sample equivalent via the scheduler’s ScheduleTellRepeatedly method. On the plus side, it provides the supervision hierarchy and provides a more natural message pipeline. With Rx it seems like having an object that is both observer and observable (i.e. is part of a pipeline), while supported, is somehow discouraged.

Reactive Extensions

In my last few posts I’ve talked about learning F#, the .NET functional programming language. I like it, but I can’t use it in a production environment for a couple of reasons:
1. Part of the project is WPF and, as I mentioned in a previous post, the WPF support isn’t there.
2. It wouldn’t be maintainable. There wouldn’t be enough people in my organization prepared to learn F# in order to support it.

Rx

I eventually came across Reactive Extensions, also called Rx. A good learning resource is www.introtorx.com. Although new to me, it’s been around for a few years. It’s a library that implements an Observer/Subscriber pattern. Observables emit data and Observers consume it via Subscribe methods. It’s like an event model but adds:

  • Advanced event consumption, e.g.
    • Sampling (fetching data each time period)
    • Buffering (accumulating data and responding only after some time period)
    • Throttling (fetching data only after some quiet period has elapsed)
    • Filtering (consuming only events that match some pattern)
  • Threading, e.g. observing and subscribing on multiple threads or on specified threads

Supposedly some of the threading functionality has been superseded by Tasks and async/await, but I like that Rx is more distributed while Tasks are still procedural.

Reactive also adds some functional sequence methods like Scan and its event filtering is like the pattern matching found in functional conditionals. It’s also functional in the sense that your observer is getting input and (presumably) producing output, like a function, though unlike a proper function an observer can have state.

Creating Observables

Creating an observer is easy. IObserver has three methods, OnNext, OnCompleted, and OnError. Simply implement the interface and handle the data in OnNext. Creating an observable yourself is a bit more tricky.

Events

One way is to create an observable out of a plain old .NET event.
Let’s say you have some event:

    public event EventHandler<DateTime> MyEvent;

You can create an observable like this:

    IObservable<DateTime> eventObservable = Observable.FromEventPattern<EventHandler<DateTime>,DateTime>(
        handler => m.MyEvent += handler,
        handler => m.MyEvent -= handler
        ).Select( eventPattern => eventPattern.EventArgs );

Observable Collections

The ReactiveUI library (search for reactiveui in NuGet) adds a ReactiveList with observable events built in. This shows how you’d listen to when items are added:

    ReactiveList<String> list = new ReactiveList<string>();
    list.ItemsAdded.Subscribe( s => Console.WriteLine( "Added {0}", s ) );

Note: You have to subscribe to one of the list’s events like ItemsAdded or ItemsRemoved. You can subscribe to the list itself, but I don’t know what events it produces.

Note also: The NuGet package is out of date as of the time of writing this post. If you just install it from NuGet you’ll get the error:

Warning 1 Reference to type ‘Splat.IEnableLogger’ claims it is defined in ‘[…]\packages\Splat.1.0.0\lib\Net45\Splat.dll’, but it could not be found c:\Projects\ReactiveDemo\packages\reactiveui-core.6.5.0\lib\Net45\ReactiveUI.dll ReactiveDemo
To fix this you have to update its dependent library, Splat, to the latest version.

Create your own Observable

If you’re going all-in on Rx and want to create your own IObservable without wrapping some other technology, there’s a way.
introtorx.com advises against implementing IObservable yourself and advises using Observable.Create instead. Here’s an example of a base class that handles using Create to provide an IObservable.

    /// <summary>
    /// Adds <see cref="IObservable{T>"/> support to a class.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public abstract class ObservableBase<T> {

        #region IObservable

        /// <summary>
        /// The list of observers.
        /// </summary>
        private readonly List<IObserver<T>> _observers = new List<IObserver<T>>();

        /// <summary>
        /// Creates an observable using <see cref="Observable.Create{TResult}(Func{System.IObserver{TResult},System.Action})"/>.
        /// </summary>
        public IObservable<T> AsObservable {
            get {
                return Observable.Create( (Func<IObserver<T>, IDisposable>)Subscribe );
            }
        }

        /// <summary>
        /// Pushes value to all observers.
        /// </summary>
        /// <param name="value"></param>
        protected void Emit( T value ) {
            _observers.ForEach( observer => observer.OnNext( value ) );
        }

        /// <summary>
        /// Used to add observers.
        /// </summary>
        /// <param name="observer"></param>
        /// <returns></returns>
        public IDisposable Subscribe( IObserver<T> observer ) {
            _observers.Add( observer );
            return Disposable.Empty;
        }

        #endregion
    }

Note that it doesn’t implement IObservable directly but provides an AsObservable method that makes use of Observable.Create.

Chaining Observables

Given its relationship to functional programming, it seems natural to want to chain Observables together so that one Observer is the next class’ Observable. After all, you’ll often use the result of one function as input to the next.

At any rate, using code like the above, this is how you might create a class that is both Observer and Observable:

    /// <summary>
    /// An class that is both Observer and Observable.
    /// </summary>
    /// <typeparam name="TIn"></typeparam>
    /// <typeparam name="TOut"></typeparam>
    public abstract class ChainedObserver<TIn,TOut> : IObserver<TIn> {
        #region IObservable

        /// <summary>
        /// The lsit of observers.
        /// </summary>
        private readonly List<IObserver<TOut>> _observers = new List<IObserver<TOut>>();

        /// <summary>
        /// Creates an observable using <see cref="Observable.Create{TResult}(Func{System.IObserver{TResult},System.Action})"/>.
        /// </summary>
        public IObservable<TOut> AsObservable {
            get {
                return Observable.Create( (Func<IObserver<TOut>, IDisposable>)Subscribe );
            }
        }

        /// <summary>
        /// Pushes value to all observers.
        /// </summary>
        /// <param name="value"></param>
        protected void Emit( TOut value ) {
            _observers.ForEach( observer => observer.OnNext( value ) );
        }

        /// <summary>
        /// Used to add observers.
        /// </summary>
        /// <param name="observer"></param>
        /// <returns></returns>
        public IDisposable Subscribe( IObserver<TOut> observer ) {
            _observers.Add( observer );
            return Disposable.Empty;
        }

        #endregion

        #region IObserver

        /// <summary>
        /// <see cref="IObserver{T}.OnCompleted"/>
        /// </summary>
        virtual public void OnCompleted() {
        }

        /// <summary>
        /// <see cref="IObserver{T}.OnError"/>
        /// </summary>
        /// <param name="error"></param>
        virtual public void OnError( Exception error ) {
        }

        /// <summary>
        /// <see cref="IObserver{T}.OnNext"/>
        /// </summary>
        /// <param name="value"></param>
        virtual public void OnNext( TIn value ) {
        }

        #endregion
    }

As before, it doesn’t implement IObservable directly but provides an AsObservable method that makes use of Observable.Create.

Roslyn Update

There have been some changes to Roslyn since my last post and some of my old examples don’t compile.

CustomWorkspace has been replaced by AdHocWorkspace

Creating a class from scratch is now:

AdhocWorkspace cw = new AdhocWorkspace();
OptionSet options = cw.Options;
options = options.WithChangedOption( CSharpFormattingOptions.NewLinesForBracesInMethods, false );
options = options.WithChangedOption( CSharpFormattingOptions.NewLinesForBracesInTypes, false );
SyntaxNode formattedNode = Formatter.Format( cu, cw, options );
StringBuilder sb = new StringBuilder();
using ( StringWriter writer = new StringWriter( sb ) ) {
    formattedNode.WriteTo( writer );
}

Note that some of the CSharpFormattingOptions syntax changed, too.
In our simple getter and setter, the BinaryExpression used for assigment is now an AssignmentExpression.

PropertyDeclarationSyntax property =
    SF.PropertyDeclaration( SF.ParseTypeName( "String" ), SF.Identifier( "A" ) )
        .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
        .AddAccessorListAccessors( 
            SF.AccessorDeclaration(
                SyntaxKind.GetAccessorDeclaration,
                SF.Block(
                    SF.List( new [] {
                        SF.ReturnStatement( SF.IdentifierName( "_a" ) )
                    } )
                )
            ),
            SF.AccessorDeclaration(
                SyntaxKind.SetAccessorDeclaration,
                SF.Block( 
                    SF.List( new [] {
                        SF.ExpressionStatement( 
                            SF.AssignmentExpression( 
                                SyntaxKind.SimpleAssignmentExpression,
                                SF.IdentifierName( "_a" ),
                                SF.IdentifierName( "value" )
                            )
                        )
                    } )
                )
            )
        )
    ;

Everything else from my old example project seems to compile.

F#, WPF, and Prism

I recently attempted to use F# to create a WPF project using the Prism MVVM library.  The project, if you want to download it or look at the code, is at https://github.com/mkb137/FSharpAndPrism.

Creating a WPF Application in F#

This isn’t too hard.  There’s no option to create an F# WPF application by default, but if you create an F# Console Application and then, in the project settings, flip it over to “Windows Application” it will run like one.

To get the WPF libraries, you have to add these references:
* PresentationCore
* PresentationFramework
* UIAutomationClient
* UIAutomationTypes
* WindowsBase
* System.Xaml

I used the FsXaml project to create usable F# types from WPF XAML files.
You can add vanilla XAML files, like App.xaml, with no backing class and then convert them to F# types via:

type App = XAML<"App.xaml", true>

Two things to be aware of:
1. All XAML files must be compiled as “Resource” (the default is None)
2. Visual Studio LIES.  As you may know, in F# the order of the files in solutions matter.  In F# projects, Visual Studio gives you “move up” and “move down” functions to put the files in order.  But once you start adding XAML files, all bets are off.  If you find the solution mysteriously failing to find libraries that it should, open your .fsproj file in a text editor and have a look at the included file order.  You may need to order it manually.

Adding Prism

I used the UnityBootstrapper, which in F# looks like this:

type Bootstrapper() =
    inherit UnityBootstrapper()
    override this.CreateShell() = 
        WindowUtils.loadComponent "/FSharpAndPrism;component/Shell.xaml"
    override this.InitializeShell() =
        base.InitializeShell()
        Application.Current.MainWindow <- ( this.Shell :?> Window )
        Application.Current.MainWindow.Show()
    override this.ConfigureContainer() =
        base.ConfigureContainer()
        this.Container.LoadConfiguration() |> ignore
        this.Container.RegisterInstance( this.Container ) |> ignore
    override this.ConfigureModuleCatalog() =
        base.ConfigureModuleCatalog()
        let moduleCatalog = this.ModuleCatalog :?> ModuleCatalog
        moduleCatalog.AddModule typedefof<AlphaModule> |> ignore

That WindowUtils.loadComponent is just a utility function to load the XAML resource:

module WindowUtils =
    let loadComponent( path ) =
    let resourceLocator = new Uri( path, UriKind.Relative )
    Application.LoadComponent( resourceLocator ) :?> DependencyObject

So I create a Shell with a MainRegion region…

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:prism="http://www.codeplex.com/prism"
    xmlns:infrastructure="clr-namespace:FSharpAndPrism.Infrastructure;assembly=FSharpAndPrism.Infrastructure"
    Title="F# Prism Demo" Height="150" Width="500"
    WindowStartupLocation="CenterScreen"
    >
    <StackPanel Orientation="Vertical">
        <Label Content="View Goes Here:"/>
        <ContentControl prism:RegionManager.RegionName="{x:Static infrastructure:RegionNames.MainRegion}"/>
    </StackPanel>
</Window>

And I create a view…

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Background="White"
    >
    <StackPanel Orientation="Horizontal">
        <Label>This is my view - Data context = </Label>
        <Label Content="{Binding}"/>
    </StackPanel>
</UserControl>

Register it as an F# type…

type MyView = XAML<"MyView.xaml",true>

And define a module that registers it with the region:

type AlphaModule( regionManager : IRegionManager, container : IUnityContainer ) =
    interface IModule with
        member this.Initialize() =
            regionManager.RegisterViewWithRegion( RegionNames.MainRegion, typedefof<MyView> ) |> ignore

And the result is… It doesn’t work.  The application runs but my view is not being loaded into the region.  Why?  Actually, with a little digging I find that the view is being loaded, it’s just not rendering.

FSharpAndPrism-Failure

FsXaml, Prism, and Unity

Problem #1 – Extra Constructor

As it turns out, when FsXaml creates a type derived from UserControl, in addition to UserControl’s void UserControl() constructor, FsXaml is adding a hidden void UserControl(FrameworkElement) constructor.  If the default configuration is not overridden, Unity will use this constructor when resolving the component and the type created with this constructor will not render itself correctly.  A simple but tedious way around this problem is to, for each view, register it with Unity so that the constructor taking no parameters is used.

container.RegisterType<MyView>( new InjectionConstructor() ) |> ignore

FSharpAndPrism-NoContext

Problem #2 – Adding a data context

Prism Views aren’t that useful with out their ViewModel data contexts and those are usually passed in the constructor.  So the first thing we want to do is subclass our the type that FsXaml created and add our own constructor.  This, by the way, solves our Unity problem as well since our subclassed type won’t have the bogus constructor that FsXaml is creating.
Here’s a basic view model type:

type MyViewModel() =
    let mutable name: string = null
    member this.Name
        with public get() = name
        and public set value = name <- value

Here’s our subclassed view (where the original has been renamed with a tick):

type MyView' = XAML<"MyView.xaml",true>

type MyView() =
    inherit MyView'()
    new( viewModel : MyViewModel ) as this =
        MyView()
        then
            this.DataContext <- viewModel

and… we have a problem.  By default, FsXaml derived types are sealed.  There’s no real reason for this other than that FsXaml is using a type provider from the fsprojects/FSharp.TypeProviders.StarterPack and it creates types as sealed for, I suppose, educational purposes.  If the “Sealed” attribute is removed from the created type it works fine.  I submitted a pull request to FsXaml who asked me to submit it upstream to FSharp.TypeProviders.StarterPack.  I submitted it a moment ago and haven’t heard back yet.  Until then, a “fixed” FsXaml implementation is at mkb137/FsXaml

Using the modified FsXaml library, it works and we have our view loaded with its data context:

FSharpAndPrism-WithDataContext

Final Problem: FSC: error FS2024: Static linking may not use assembly that targets different profile.

A normal WPF project is compiled against the .NET 4.5 profile which is known internally as Profile7 (see a list of PCL profiles here.  If you attempt to directly use any third-party library that is compiled not just for .NET 4.5, but for .NET 4.5 and Windows Phone (e.g. Profile78), you’ll get the error that you would never see in the same C# project:

FSC: error FS2024: Static linking may not use assembly that targets different profile.

And there’s no way around it as far as I know.  The bug has been logged here on F#’s current home on GitHub, and not yet fixed.

Outlook Add-In for Replicon

My employer uses Replicon to track hours against projects and tasks. Its web-based user interface is…adequate. Entering time in an online calendar is fine but I already have an electronic calendar open all day: Microsoft Outlook.

I started a project to create an add-in that adds an “Add to Replicon” menu item to the Outlook calendar. The Replicon Repliconnect API is used to get project and task information and to send the timesheet information back to the server.

It’s still a work in progress. The initial code is up here.

Fault-safe WCF Proxy Generator for Service Reference clients

WCF is great, but if a connection ever throws an exception for any reason it puts the client in the Faulted state and the client has to be aborted and recreated. It’s a pain in the ass since this can happen anywhere a client method is called.
In a previous post, I showed the dynamic generation of a proxy for a WCF channel.

Nowadays, I suspect most people create their clients using “Add Service Reference”. This generates a ClientBase client that suffers from the same problem as raw channels – if there’s ever an exception, you need to recreate the instance.

Following the earlier post, I created code to use the CIL Emit libraries to dynamically generate a fault-tolerant proxy around a given client. If an exception is thrown, the client is recreated with the correct authentication and whatever settings were used to construct it in the first place.
The code is up on github.

Code Generation with Roslyn – If, Else, and Loops

if statements

This:

MethodDeclarationSyntax method = SF.MethodDeclaration(
    SF.PredefinedType( SF.Token( SyntaxKind.VoidKeyword ) ),
    "MyMethod"
    )
    .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
    .AddBodyStatements( 
        SF.IfStatement(
            SF.BinaryExpression( 
                SyntaxKind.EqualsExpression,
                SF.IdentifierName( "_a" ),
                SF.LiteralExpression( SyntaxKind.NumericLiteralExpression, SF.Literal( "X" ) )
            ),
            SF.Block(  
            )
        )
    )
    ;

Will get you this:

public void MyMethod() {
    if (_a == "X") {
    }
}

if-else statements

This:

MethodDeclarationSyntax method = SF.MethodDeclaration(
    SF.PredefinedType( SF.Token( SyntaxKind.VoidKeyword ) ),
    "MyMethod"
    )
    .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
    .AddBodyStatements( 
        SF.IfStatement(
            SF.BinaryExpression( 
                SyntaxKind.EqualsExpression,
                SF.IdentifierName( "_a" ),
                SF.LiteralExpression( SyntaxKind.NumericLiteralExpression, SF.Literal( "X" ) )
            ),
            SF.Block(  
            ),
            SF.ElseClause( 
                SF.Token( SyntaxKind.ElseKeyword ),
                SF.IfStatement( 
                    SF.BinaryExpression( 
                        SyntaxKind.EqualsExpression,
                        SF.IdentifierName( "_a" ),
                        SF.LiteralExpression( SyntaxKind.NumericLiteralExpression, SF.Literal( "Y" ) )
                    ),
                    SF.Block(  
                    ),
                    SF.ElseClause(
                        SF.Token( SyntaxKind.ElseKeyword ),
                        SF.Block( 
                        )
                    )
                )
            )
        )
    )

Will get you this:

public void MyMethod() {
    if (_a == "X") {
    }
    else if (_a == "Y") {
    }
    else {
    }
}

for loops

This:

MethodDeclarationSyntax method = SF.MethodDeclaration(
    SF.PredefinedType( SF.Token( SyntaxKind.VoidKeyword ) ),
    "MyMethod"
    )
    .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
    .AddBodyStatements( 
        SF.ForStatement(
            SF.VariableDeclaration( 
                SF.PredefinedType( SF.Token( SyntaxKind.IntKeyword ) ), 
                SF.SeparatedList(new [] {
                    SF.VariableDeclarator(
                        SF.Identifier( "i" ),
                        null,
                        SF.EqualsValueClause( SF.LiteralExpression( SyntaxKind.NumericLiteralExpression, SF.Literal( 0 ) ) ) 
                    )
                } )
            ),
            SF.SeparatedList<ExpressionSyntax>(),
            SF.BinaryExpression( 
                SyntaxKind.LessThanExpression,
                SF.IdentifierName( "i" ),
                SF.LiteralExpression( SyntaxKind.NumericLiteralExpression, SF.Literal( 10 ) )
            ),
            SF.SeparatedList<ExpressionSyntax>( new [] {
                SF.PostfixUnaryExpression(
                    SyntaxKind.PostIncrementExpression,
                    SF.IdentifierName( "i" )
                )
            } ),
            SF.Block(  
            )
        )
    )

Will get you this:

public void MyMethod() {
    for (int i = 0; i < 10; i++) {
    }
}

foreach loops

This defines our generic list:

LocalDeclarationStatementSyntax listDeclaration = SF.LocalDeclarationStatement(
    SF.TokenList(),
    SF.VariableDeclaration( 
        SF.GenericName( 
            SF.Identifier( "IList" ), 
            SF.TypeArgumentList( 
                SF.SeparatedList<TypeSyntax>( new [] { SF.PredefinedType( SF.Token( SyntaxKind.StringKeyword ) ) } ) 
            ) 
        ), 
        SF.SeparatedList( new [] {
            SF.VariableDeclarator(
                SF.Identifier( "list" ),
                null,
                SF.EqualsValueClause( 
                    SF.ObjectCreationExpression(
                        SF.Token( SyntaxKind.NewKeyword ),
                        SF.GenericName( 
                            SF.Identifier( "List" ), 
                            SF.TypeArgumentList( 
                                SF.SeparatedList<TypeSyntax>( new [] { SF.PredefinedType( SF.Token( SyntaxKind.StringKeyword ) ) } ) 
                            ) 
                        ),
                        SF.ArgumentList( SF.SeparatedList<ArgumentSyntax>( new ArgumentSyntax[0] ) ),
                        null
                    )
                )
            )
        } )
    )
);

And this our “foreach”:

ForEachStatementSyntax forEachStatement = SF.ForEachStatement(
    SF.PredefinedType( SF.Token( SyntaxKind.StringKeyword ) ),
    SF.Identifier( "item" ),
    SF.IdentifierName( "list" ),
    SF.Block()
);

Adding both to a method:

MethodDeclarationSyntax method = SF.MethodDeclaration(
    SF.PredefinedType( SF.Token( SyntaxKind.VoidKeyword ) ),
    "MyMethod"
    )
    .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
    .AddBodyStatements( 
        listDeclaration,
        forEachStatement
    );

Will get you this:

public void MyMethod() {
    IList<string> list = new List<string>();
    foreach (string item in list) {
    }
}

while loops

This is one of the more straightforward ones.
This:

MethodDeclarationSyntax method = SF.MethodDeclaration(
    SF.PredefinedType( SF.Token( SyntaxKind.VoidKeyword ) ),
    "MyMethod"
    )
    .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
    .AddBodyStatements( 
        SF.WhileStatement( 
            SF.LiteralExpression( SyntaxKind.TrueLiteralExpression ),
            SF.Block(  
                SF.BreakStatement()
            )
        )
    );

Will get you this:

public void MyMethod() {
    while (true) {
        break;
    }
}

Code Generation with Roslyn – Fields and Properties

I’m going to give a few more basic examples of code generation with Roslyn. The following assume that you have a ClassGenerationSyntax variable named “@class”. The examples have also shortened SyntaxFactory to SF using:

using SF = Microsoft.CodeAnalysis.CSharp.SyntaxFactory;

Properties

The code

// Add a property
PropertyDeclarationSyntax @property = SF.PropertyDeclaration( SF.ParseTypeName( "String" ), "MyProperty"  )
    .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) );
// Add a getter
@property = @property.AddAccessorListAccessors(
    SF.AccessorDeclaration( SyntaxKind.GetAccessorDeclaration )
        .WithSemicolonToken( SF.Token(SyntaxKind.SemicolonToken ) 
        ) );
// Add a private setter
@property = @property.AddAccessorListAccessors( 
    SF.AccessorDeclaration( SyntaxKind.SetAccessorDeclaration )
    .AddModifiers( SF.Token( SyntaxKind.PrivateKeyword ) )
    .WithSemicolonToken( SF.Token(SyntaxKind.SemicolonToken ) 
    ) );
// Add the property to the class
@class = @class.AddMembers( @property );

Produces the code:

public class MyClass {
    public String MyProperty { get; private set; }
}

Variables

This adds a simple field to the class:

FieldDeclarationSyntax aField = SF.FieldDeclaration( 
    SF.VariableDeclaration( 
        SF.ParseTypeName( "String" ), 
        SF.SeparatedList(new [] { SF.VariableDeclarator( SF.Identifier( "_a" ) ) } )
    ) )
    .AddModifiers( SF.Token( SyntaxKind.PrivateKeyword ) );
@class = @class.AddMembers( aField );

Generating the code:

private String _a;

This code initializes the field to a new object:

ExpressionSyntax initializationExpression = SF.ObjectCreationExpression(
    SF.Token( SyntaxKind.NewKeyword ),
    SF.ParseTypeName( "OtherClass" ),
    SF.ArgumentList( SF.SeparatedList<ArgumentSyntax>( new [] {
        SF.Argument( SF.LiteralExpression( SyntaxKind.NumericLiteralExpression, SF.Literal( 1 ) ) ),
        SF.Argument( SF.LiteralExpression( SyntaxKind.StringLiteralExpression, SF.Literal( "abc" ) ) )
    } ) ),
    null
    );
FieldDeclarationSyntax bField = SF.FieldDeclaration( 
    SF.VariableDeclaration( 
        SF.ParseTypeName( "OtherClass" ), 
        SF.SeparatedList(new [] {
            SF.VariableDeclarator(
                SF.Identifier( "_b" ),
                null,
                SF.EqualsValueClause( initializationExpression ) 
            )
        } )
    ) )
    .AddModifiers( SF.Token( SyntaxKind.PrivateKeyword ) )
    .AddModifiers( SF.Token( SyntaxKind.ReadOnlyKeyword ) )
    ;
@class = @class.AddMembers( bField );

Generating the code:

private readonly OtherClass _b = new OtherClass(1, "abc");

Field-backed Properties

The following code generates a getter and setter backed by a field:

PropertyDeclarationSyntax property =
    SF.PropertyDeclaration( SF.ParseTypeName( "String" ), SF.Identifier( "A" ) )
        .AddModifiers( SF.Token( SyntaxKind.PublicKeyword ) )
        .AddAccessorListAccessors( 
            SF.AccessorDeclaration(
                SyntaxKind.GetAccessorDeclaration,
                SF.Block(
                    SF.List( new [] {
                        SF.ReturnStatement( SF.IdentifierName( "_a" ) )
                    } )
                )
            ),
            SF.AccessorDeclaration(
                SyntaxKind.SetAccessorDeclaration,
                SF.Block( 
                    SF.List( new [] {
                        SF.ExpressionStatement( 
                            SF.BinaryExpression( 
                                SyntaxKind.SimpleAssignmentExpression,
                                SF.IdentifierName( "_a" ),
                                SF.IdentifierName( "value" )
                            )
                        )
                    } )
                )
            )
        )
    ;

Producing the following code:

public String A {
    get {
        return _a;
    }

    set {
        _a = value;
    }
}

The ratio of code to output shows that it would be a lot easier to generate code from scratch with TextWriter.