Using Autofac with Xamarin

Good news is that Autofac, my IoC container of choice, works with Xamarin and even within Portable Class Library.  However there is one potential pitfall and it seems it happens at least when you use factories.

Imagine resolving ITubo defined as:

public class Tubo: ITubo
    public Tubo(Func<ITubo> tuboFactory)

public interface ITubo

Note the use of factory through Func<ITubo>. In this case Autofac uses reflection and perhaps some runtime IL code generation. Now, try running the following piece of code on Xamarin.Android:

ContainerBuilder builder = new ContainerBuilder();
var container = builder.Build();

It is simple registration and after that I do resolve the interface. When you run this code it will most probably work. But that’s only because you are running it in Debug configuration. Now try running in in Release configuration. It will most probably throw an exception at you:

Autofac.Core.DependencyResolutionException: An exception was thrown while executing a resolve operation.

Not very informative but at least the call stack shows that problem happens within System.Core assembly. And it isn’t Autofac’s fault at all.

The reason for the problem is simple but perhaps not the most obvious one. Default project settings are that at Release configuration it cuts out all of the unused code from SDK libraries (Xamarin stuff which is basically all .net BCL) and combines all of the assemblies into a single file - through its linker (at Debug time it uses shared libraries as would .net on Windows). And since Autofac is doing operations at runtime (at least when it comes to factories), linker doesn’t see those and simply cuts off unused types at compilation time to reduce the output size. Read more about Xamarin linking process here:


The nasty part is that you won’t know what types are cut off until you run the application in Release configuration. Remember, always try your applications in Release configuration!

The solution

Anyway, the solution is, as I’ve found out, rather simple. Just instruct linker to leave alone (don’t optimize) System.Core assembly. If you are using Visual Studio the go to Project/Properties, Android Options tab and enter System.Core text into Skip linking assemblies text box. If you are using Xamarin IDE the go to Project/Properies, Build/Android Build tab, Linker subtab and enter the same System.Core into Ignore Assemblies text box (didn’t try this one). That’s it, linker will leave alone that assembly and Autofac will happily run even in Release configuration.

Luckily the difference in output file size isn’t that significant: 450KB in worst case.

Invoking DatePickerDialog asynchronously with Xamarin.Android

Invoking a DatePickerDialog in Xamarin.Android is a bit tricky because it is done through callbacks and at the end one has to dispose it as well. Hence I present asynchronous extension methods PickDateAsync and PickDateAndAssignAsync.

With my code you can use this syntax and don’t worry about DatePickerDialog disposal:

EditText et1 = FindViewById<EditText>(Resource.Id.editText1);
await et1.PickDateAndAssignAsync();

There is also an overload that accepts an instance of CancellationToken. Here are the methods:

public static class DatePickerExtension
    public static Task<DateTime> PickDateAsync(this EditText dateEdit)
        return dateEdit.PickDateAsync(CancellationToken.None);
    public static Task<DateTime> PickDateAsync(this EditText dateEdit, CancellationToken ct)
        TaskCompletionSource<DateTime> tsc = new TaskCompletionSource<DateTime>();
        DatePickerDialog picker = null;
        DateTime current;
        if (!DateTime.TryParse(dateEdit.Text, out current))
            current = DateTime.Now;
        picker = new DatePickerDialog(dateEdit.Context, (sender, e) =>
            if (tsc != null)
                if (ct.IsCancellationRequested)
                tsc = null;
        }, current.Year,current.Month-1,current.Day);
        return tsc.Task;

    public static Task PickDateAndAssignAsync(this EditText dateEdit)
        return dateEdit.PickDateAndAssignAsync(CancellationToken.None);
    public static async Task PickDateAndAssignAsync(this EditText dateEdit, CancellationToken ct)
        DateTime date = await dateEdit.PickDateAsync(ct);
        if (!ct.IsCancellationRequested)
            dateEdit.Text = date.ToString("d");
Enjoy awesome asynchronous C#/.net support.

Running DevExtreme as MVC project in simulator

DevExtreme has a nice (web) simulator that lets you preview your application on a target device (tablet, phone, iOS, Android).


That’s really nice. However, out of the box, it works only when you have a special type of Visual Studio project that comes with DevExtreme (when you create a new DevExtreme project through one of its templates). Which might be a problem if you have other project type (i.e. MVC) instead – DevExtreme project is meant for distribution as a packaged “native” application. In that case no simulator for you, at least not out of the box.

Luckily here is a simple solution how to enable simulator for any web project. The mandatory step is to

  • find WebServer folder that is part of DevExtreme extension for Visual Studio. Mine is located in C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\Extensions\mblaqgom.mw5.
  • from WebServer folder found in step above copy simulator.html and Images and Simulator folders to root of your MVC project.
  • Do not copy web.config – it will wreck your application

That’s it. You can run your application by going to URL/simulator.html?appPage=index.html (assuming your starting page is index.html). Note that you can pass other parameters to simulator as well, like device=iPhone and orientation=p..

If you want to omit the appPage=index.html parameter you can rename index.html to app.html and simulator will pick app.html by default.

Incoming TypeScript definitions for PhoneJS and ChartJS (DevExtreme)

PhoneJS along with ChartJS are DevExpress’ efforts in providing single page web applications for mobile platforms (think Tablets and Phones).  Together they are combined into DevExtreme combo. In practice they are pure javascript libraries without ties to any server side platform - which is good, are built with KnockoutJS, jQuery in mind, etc (really plenty of nice features, check hyperlinks). And they can be packed into “native” applications for various platforms using PhoneGap. Added bonus is an emulator (again in javascript) that let’s your preview applications. Everything you need to run projects based on DevExtreme is a web server. Any web server on any OS since they are client side stuff.

I recently poked around this technologies and I soon felt that one, rather important feature (well, to me at least) was missing. Typescript definition files were missing. Until now that is. They are coming with v13.2 and you can already preview them in beta. Plus, there is a template that let’s you start your project with Typescript code instead of Javascript. While this doesn’t seem a big deal, well, it is. Typescript is a huge boost for javascript development, more so when it comes to bigger projects. Hence it is a big deal to be able to use all of Typescript goodies with DevExtreme goodies. And now I can.

Other improvements are coming as well (improved theming, improved and new widgets, localization…). While I can’t call myself experienced in DevExtreme it will be definitely my first choice for new projects.

Solving Blend 2013 interactivity error

I am playing with Blend 2013 Silverlight Sketchflow for creating web application mockups. Recently I’ve stumbled into an curios error when adding interactivity to a button.

Here is the repro:

Create two screens, and a button on a screen. So far so good. Right click on that button and select Navigate To/Screen 2. Blend will add a navigational behavior, like:

    <i:EventTrigger EventName="Click">
TargetScreen="SilverlightPrototype2Screens.Screen_1"/> </i:EventTrigger> </i:Interaction.Triggers>

It will underline pi:NavigateToScreenAction with a red squiggle as well complaining that type NavigateToScreenAction from assembly Microsoft.Expression.Prototyping.Interactivity is built with an older version of the Blend SDK, and it is not supported in Silverlight 5 projects.

A puzzling error. After playing around I discovered that the problem is with the referenced System.Windows.Interactivity assembly. Somehow Blend added a reference to a version instead of

Not sure what triggered the referencing of the wrong version but the solution is quite simple. Just remove it (in both projects) and reference the proper version. And Blend application sparks to life again.

Investigating why an instance is kept alive in a .net application

Sometimes, when I want to verify .net memory management behavior, I fire up ANTS Memory Profiler and run it on a test application just to see how memory management behaves.

So today I went and created this application

class Program
    static void Main(string[] args)
        A a = new A();
        B b = new B { Pointer = a };
        b.Pointer = null;
        b = null;
        a = null;
        a = new A();

class A


class B
    public A Pointer;

The ReadLine calls allow me to hit the “Take Memory Snapshot” in profiler. Later I examined these snapshots, specially the one between One and Two. What would you expect, how many instances are alive at that point? I’d say one, the instance of class A (referenced by a).

However, the profiler was showing, surprisingly, two. According to it, both an instance of A and an instance of B, were still very much alive. This result surprised me. Even more surprisingly, after Four there was still an instance of B around. How is this possible? There are no references to b and it is pointing to null. A bug in Memory Profiler? Hardly possible.

Right before I was going to post a question on RedGate’s forum I decided to check the IL code. With .net reflector of course. Immediately I saw the reason for that odd behavior. Can you spot it?

.method private hidebysig static void Main(string[] args) cil managed
    .maxstack 2
    .locals init (
        [0] class ConsoleApplication213.A a,
        [1] class ConsoleApplication213.B b,
        [2] class ConsoleApplication213.B b2)
    L_0000: nop 
    L_0001: newobj instance void ConsoleApplication213.A::.ctor()
    L_0006: stloc.0 
    L_0007: newobj instance void ConsoleApplication213.B::.ctor()
    L_000c: stloc.2 
    L_000d: ldloc.2 
    L_000e: ldloc.0 
    L_000f: stfld class ConsoleApplication213.A ConsoleApplication213.B::Pointer
    L_0014: ldloc.2 
    L_0015: stloc.1 
    L_0016: ldstr "One"
    L_001b: call void [mscorlib]System.Console::WriteLine(string)
    L_0020: nop 
    L_0021: call string [mscorlib]System.Console::ReadLine()
    L_0026: pop 
    L_0027: ldloc.1 
    L_0028: ldnull 
    L_0029: stfld class ConsoleApplication213.A ConsoleApplication213.B::Pointer
    L_002e: ldnull 
    L_002f: stloc.1 
    L_0030: ldstr "Two"
    L_0035: call void [mscorlib]System.Console::WriteLine(string)
    L_003a: nop 
    L_003b: call string [mscorlib]System.Console::ReadLine()
    L_0040: pop 

For some reason, compiler decided to allocate two references for class B: local variables b and b2. When the instance of class B is created it is stored in b2. After the Pointer property is assigned the same reference is stored to b while b2 isn’t set to null. Then when b is set to null, the b2 is still very much alive and thus keeping the instances count for class B to 1 – even though b is null and there are no other C# variables for referencing instances of B.

Mystery solved.  The lessons learned are that compiler might generate code one wouldn’t expect and that profiling memory isn’t always black and white. Those 50 shades of gray happen as well. IOW experience and good understanding of .net is a necessity.

When .net assemblies aren’t properly versioned odd errors happen

Today I’ve upgraded a SignalR library from 1.x to 2.0 in an MVC 5 (server) and WPF (client) projects I am developing. The upgrade itself went smooth but afterwards the client started yielding odd errors and refusing to connect anymore. It was yielding an exception saying something like Transport Connection time out (I can’t remember the exact message). Since it was a rather simple upgrade this error made no sense. Google didn’t help much either.

So I went debugging.


First step is to create a simple repro sample – a solution with a basic server and a console client (see attached zip).

Second step is to turn on SignalR tracing on client:

hubConnection.TraceLevel = TraceLevels.All;
hubConnection.TraceWriter = Console.Out;

Armed with these two steps I was able to get an error that made a bit more sense although it was even more bizzare.

18:43:53.9073548 - null - ChangeState(Disconnected, Connecting)
18:43:55.4913444 - b8fd1874-483d-4d89-8a69-c2cfe33cf946 - WS Connecting to: ws://localhost:53705/signalr/connect?transport=webSockets&connectionToken=0dQ3scw2aJ7RbXuUsTfa4wlY%2FJlMzW%2FVL1sVb%2FyswewEO8n4qAth7Erpt0ga0laLV%2B8BCD833lZZy1MblOe0HuQs0O1mYi%2FfiiLSHc5%2F%2B1wk6tUsbFxMKVQFwRO9BvSW&connectionData=[{"Name":"formsHub"}] 18:43:55.5800651 - b8fd1874-483d-4d89-8a69-c2cfe33cf946 - WS: OnMessage({"C":"d-5AB67EA2-B,0|C,0|D,1|E,0","S":1,"M":[]})
18:43:55.5940751 - b8fd1874-483d-4d89-8a69-c2cfe33cf946 - OnError(System.MissingMethodException: Method not found: 'System.Collections.Generic.IEnumerator`1 Newtonsoft.Json.Linq.JArray.GetEnumerator()'. at Microsoft.AspNet.SignalR.Client.Transports.TransportHelper.ProcessResponse(IConnection connection, String response, Boolean& shouldReconnect, Boolean& disconnected, Action onInitialized) at Microsoft.AspNet.SignalR.Client.Transports.WebSocketTransport.OnMessage(String message) at Microsoft.AspNet.SignalR.WebSockets.WebSocketHandler.d__e.MoveNext())
18:43:55.6110864 - b8fd1874-483d-4d89-8a69-c2cfe33cf946 - WS: OnClose()

It says something like – I can’t find a method in the Newtonsoft.Json assembly. That’s totally weird as this kind of error should be handled at compile time.

I went looking into Newtonsoft.Json assembly referenced by SignalR 2.0. It correctly references version 5.0.8. The assembly in package folder has the method it was mentioned as missing. Mystery. One thing that caught my eye  while .net reflecting the assembly was its version. While the file version is 5.0.8. the assembly version is, oddly, How come?

Fourth step was looking into modules loaded by my application. They are listed through Visual Studio-Debug/Windows/Modules. Amazingly, Visual Studio was listing Newtonsoft.Json v4.05.8.15203 from … GAC. Not from my package. And by looking at its date it was clear that it was an older version (4.8.2012). Heck, I didn’t even know it was in GAC. I didn’t put it, some other app had to.


From previous Googling I remembered an explanation somewhere that the missing GetEnumerator method was introduced in version 5.0.5. So this was probably it – .net was loading an older version from GAC - that was really missing that method. At this point I knew what was wrong.

Just in case, to make sure, I checked whether the assembly really was in GAC:

C:\Windows\system32>gacutil /l newtonsoft.json
Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.18020
Copyright (c) Microsoft Corporation.  All rights reserved.

The Global Assembly Cache contains the following assemblies:
  newtonsoft.json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, processorArchi

Number of items = 1

It was.


The proper way would be to have a properly versioned Newtonsoft.Json assembly (those are strong key signed as well). That’s why there is versioning and .net wouldn’t make this confusion. I really wonder why James uses the same assembly version for assemblies that should really have different signatures. Hopefully he will fix this problem in next versions. But until then there is …

… the next best way is to force .net to not load it from GAC.  If the assembly is removed from GAC, .net won’t find the wrong version anymore. See, .net always tries GAC first and only if it doesn’t find a suitable assembly it will go looking elsewhere, like into the folder where your application is. Perhaps I could configure it to load the proper assembly through .config file but this solution is better – it’ll solve the problem unless an older newtonsoft.json is reinstalled again in GAC. Hm.

Removing assembly from GAC should be a rather simple process. Just fire

GACUTIL /U Newtonsoft.Json

and it should be removed. But not this time. Instead I got this warning:

C:\Windows\system32>gacutil /u newtonsoft.json
Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.18020
Copyright (c) Microsoft Corporation.  All rights reserved.

Assembly: newtonsoft.json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, proces
Unable to uninstall: assembly is required by one or more applications
Pending references:
              SCHEME: <WINDOWS_INSTALLER>  ID: <MSI>  DESCRIPTION : <Windows Installer>
Number of assemblies uninstalled = 0
Number of failures = 0

Basically it is saying that some installed application did install it into GAC and now it is preventing me from removing it from GAC. Uf, nasty. To make it worse, it doesn’t say which application. This article lists the way to “unreference it” to be able to remove it from GAC. Basically you have to remove its entry from the registry and then execute gacutil removal command again.


After registry modification it succeeded.

C:\Windows\system32>gacutil /u newtonsoft.json
Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.18020
Copyright (c) Microsoft Corporation.  All rights reserved.

Assembly: newtonsoft.json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, proces
Uninstalled: newtonsoft.json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, pro
Number of assemblies uninstalled = 1
Number of failures = 0

The aftermath

Removing that old Newtonsoft.Json from registry did the trick. SignalR works like charm again. However, I had to manually remove a component of an unidentified application. And this removal might cause problems with that application in the future.

I really hope that Newtonsoft.Json gets proper versioning to avoid situations like this. This should be a lesson to every library developer out there – do use proper version numbering!. (4.69 mb)


12.11.2013: James, the author, is looking at the possible solution. See

Android activity life cycle and IoC

I was recently working on an Android (Xamarin, .net) application based on MvvmCross framework. Actually not just an Android app since it could be ported quite easily to other platforms, such as Windows Phone 8 or IPhone. Anyway, I was using inversion of control principle in a slightly incorrect way and thus done a mistake which revealed only a while after the deployment.

Here are the symptoms: Application would cold start fine, would resume fine when resume was done within reasonable time (no idea, depends on the device, in my case could be hours and it would work perfectly) but it wouldn’t resume well if the timespan was too much (i.e. a day or several hours). Instead of displaying the activity content it was just an actionbar with title without any content of menuitems.

By looking at android’s log on the device itself it was clear that there were problems with IoC resolve method. It yielded an “Object reference null” type of exception. I was resolving the reference within activity’s constructor. Odd error, since MvvmCross is supposed to trigger IoC registration  before the first activity is run. But somehow it wasn’t. I’ve mentioned that to Stuart (@slodge, man behind MvvmCross) and he instantly pointed to the mistake I made – I neglected the Android activity’s lifecycle. I immediately understood my mistake: I am used to put IoC references within constructors as arguments, which is mostly fine. Except when it comes to Android activities. The thing is that the entry point of a suspended application (with activity destroyed) is the activity itself, more precisely, its constructor. MvvmCross does trigger the IoC registration method correcly, but, of course, only after the activity is created and hence I was having errors in this particular situation.

The solution is fairly simple – move IoC resolving within OnCreate method, not sooner – that’s the point where you can be certain that MvvmCross initialization is done.


public abstract class SomeClass<T> : Activity
    protected readonly IFragmentPresenter fragmentPresenter;

    public MvxActivityFragmentHost(): this(Mvx.Resolve<IFragmentPresenter>())

    public MvxActivityFragmentHost(IFragmentPresenter fragmentPresenter)
        this.fragmentPresenter= fragmentPresenter;


public abstract class SomeClass<T> : Activity
    protected IFragmentPresenter fragmentPresenter;

    protected override void OnCreate (Bundle bundle)
        base.OnCreate (bundle);
        fragmentPresenter = Mvx.Resolve<IFragmentPresenter>();

This change did the trick. A bit more work to inject the mock reference when testing but not a big deal.

Now, if you followed the post you might be asking, why the heck does application cold starts just fine, since it should get the same error. The explanation is rather simple – I am using a splashscreen activity when application cold starts. This one doesn’t have any IoC resolving involved at all, but it does initialize MvvmCross. So when it gets to the my problematic activity, the IoC is already in place.

Now, there you have it. Respect the Android activity lifecycle otherwise it will bit you.

Visual Studio 2013 brings IntelliSense for Data Binding to XAML editor

One of the better improvements in Visual Studio 2013 is IntelliSense for data binding in XAML editor. The improvement is described in this blog post. Very nice. But what article fails to mention is how does one get that mystical d namespace. In face, it is not exactly easy to find the proper declaration.

After some googling around I have found this declaration:


Then I tried applying a d:DataContext to the first element on the default window template – Grid, like:

<Grid d:DataContext="{d:DesignInstance Type=local:Tubo}">
    <TextBlock Text="{Binding Xul}"

That is supposed to work, but it doesn't (I have a simple class Tubo with a single property Xul in local namespace). Instead of compiling it was throwing this error at me:

The property 'DataContext' must be in the default namespace or in the element namespace ''.

Yeah, right. After some more googling I found that I had to add another namespace and a ignore property to the mix:


These two lines did the trick, error was gone, the project compiled and IntelliSense was alive.

Here is my whole XAML:

<Window x:Class="WpfApplication73.MainWindow"
        Title="MainWindow" Height="350" Width="525">
    <Grid d:DataContext="{d:DesignInstance Type=local:Tubo}">
        <TextBlock Text="{Binding Xul}"

Hopefully this post will spare some time for others trying to achieve the IntelliSense…

Righthand’s DataSet Debugger Visualizer supports VS2013

Highlights from new version to 1.0.11.

  • added VS2013 version
  • added a "separated assembly" versions. Until now I was using RedGate's Smart Assembly to pack all referenced assemblies into a single DLL file for easier management and distribution. However, this black magic might cause problems in certain situations (Visual Studio add-ins screams for problems). Thus I've added another set that features assemblies in separate files. The bottom line, if you have problems or you want to be on the safe side, use the later set.

Go nuts!