HttpClient and Xamarin.iOS Unified

I was creating a NuGet that was dependent on several other NuGets, one of them being Microsoft.Net.Http. This brings in the great HttpClient for all platforms.

However, there is a small problem right now: Microsoft has not yet updated their NuGet to support Xamarin.iOS Unified. They are working on it, but in the meantime what can we do to still create a NuGet that relies on HttpClient?

Well, we don’t actually need the Microsoft.Net.Http NuGet on the Xamarin platforms as the HttpClient type comes with the actual framework. This is because the Xamarin platforms target the 4.5 version of .NET.

So, we can update our .nuspec to exclude these NuGet dependencies on the Xamarin platforms. If our current .nuspec is similar to this:

    <dependency id="Microsoft.Bcl" version="1.1.9" />
    <dependency id="Microsoft.Bcl.Build" version="1.0.14" />
    <dependency id="Microsoft.Bcl.Compression" version="3.9.85" />
    <dependency id="Microsoft.Net.Http" version="2.2.28" />
    <dependency id="Rx-Core" version="2.2.5" />
    <dependency id="Rx-Interfaces" version="2.2.5" />
    <dependency id="Rx-Linq" version="2.2.5" />
    <dependency id="Rx-Main" version="2.2.5" />
    <dependency id="Rx-PlatformServices" version="2.2.5" />

All we have to do is move it into a general “ and add a specific group to the offending Xamarin.iOS platform:

    <!-- for all platforms -->
        <dependency id="Microsoft.Bcl" version="1.1.9" />
        <dependency id="Microsoft.Bcl.Build" version="1.0.14" />
        <dependency id="Microsoft.Bcl.Compression" version="3.9.85" />
        <dependency id="Microsoft.Net.Http" version="2.2.28" />
        <dependency id="Rx-Core" version="2.2.5" />
        <dependency id="Rx-Interfaces" version="2.2.5" />
        <dependency id="Rx-Linq" version="2.2.5" />
        <dependency id="Rx-Main" version="2.2.5" />
        <dependency id="Rx-PlatformServices" version="2.2.5" />
    <!-- no Microsoft on iOS Unified -->
    <group targetFramework="XamariniOS1.0">
        <dependency id="Rx-Core" version="2.2.5" />
        <dependency id="Rx-Interfaces" version="2.2.5" />
        <dependency id="Rx-Linq" version="2.2.5" />
        <dependency id="Rx-Main" version="2.2.5" />
        <dependency id="Rx-PlatformServices" version="2.2.5" />

This works, as NuGet will use the more specific for Xamarin.iOS, but fall back to the empty for all other platforms. We can use this mechanism for all platforms. We can even use this for the various files as well. In fact, this is how Microsoft does it now: They include everything for all platforms, and then exclude the specific ones that already have HttpClient built in.

When Microsoft updates their NuGet, all we need to do is drop the “ group from the .nuspec and everything is back to normal.

Flurry Analytics Portable

We all know about Flurry Analytics, and we know how we can use this with Xamarin in iOS and Android, as well as on Windows Phone.

Well, now there is a portable version that allows the analytics to be implemented in portable class libraries! The portable API abstracts away all the platform differences, but keeps all the power of the Flurry!

This can be found on NuGet and on GitHub.


The features of the portable API are the same as the native API’s, as the portable is more of an abstraction than anything else. So along with all the native features, there are a few nice new once that make the API easier to use.

This is the primary advantage of this library, it allows the analytics to be implemented in portable projects. This is especially useful if you are using a cross-platform framework, such as MvvmCross. There is a sample that you can check out that makes use of all the features.

Starting Sessions

Although the library is portable, each platform needs to start the analytics session natively/differently:

For iOS, it is very simple call StartSession from the AppDelegate:

    AnalyticsApi.StartSession("[API KEY]");

For Android, there are two ways to do this. Either by overriding the OnStart and OnStop methods from each Activity:

    // in OnStart
    AnalyticsApi.StartSession(this, "[API KEY]");

    // in OnStop

Or, by using the IActivityLifecycleCallbacks for the Application. This way allows you to start and end the session without having to implement the logic in each Activity. However it is only available from API Level 14 / Android 4.0 / Ice Cream Sandwich.

For Windows Phone, starting the session is done by attaching the StartSession method call to the Launching and Activated events:

    PhoneApplicationService.Current.Launching += (sender, args) => AnalyticsApi.StartSession();
    PhoneApplicationService.Current.Activated += (sender, args) => AnalyticsApi.StartSession();

For each of the platforms, there is also a way to pass the key in to the API, but only start the session later:

    // somewhere in the code
    AnalyticsApi.ApiKey = "[API KEY]";

    // and then a little later

There is also a boolean property, IsSupported, that will return true if the platform supports Flurry Analytics:

    if (!Analytics.IsSupported)
        Debug.WriteLine("PLatform does not support Flurry, nothing will be tracked.");

Setting Up Analytics

There are a few methods that hide the platform differences. Some examples of this are in the setting of user details, such as SetAppVersion, SetUserId, SetLocation, SetAge and SetGender.

Not only that, there are a few methods that specify how Flurry should communicate, such as SetSessionContinueTimeout and EnableSecureTransport.

Usually these methods should be called before starting the session.

Logging Events & Errors

Along with tracking basic analytics, events and errors can be tracked. There are a few methods that support this: LogPageView, LogEvent, LogTimedEvent, EndTimedEvent and LogError.

Logging timed events has been made much easier by implementing a new pattern for doing this. By calling LogTimedEvent in a using block, you can end the event in case of any exceptions as well as removing an extra call:

    using (AnalyticsApi.LogTimedEvent("EventId"))
        // perform a long running task

Before, you would have to ensure that you called EndTimedEvent to avoid any problems:

        // perform the long running task

Parameters can also be passed with the events using a simple Dictionary:

    var parameters = new Dictionary<string, string> 
        {"ParameterKey", "ParameterValue"}
        {"AnotherParameterKey", "AnotherParameterValue"}
    AnalyticsApi.LogEvent("EventId", parameters);

Flurry.Analytics for Xamarin

The Flurry Analytics Agent allows you to track the usage and behavior of your Android, iOS or Windows Phone application on users’ phones for viewing in the Flurry Analytics system. It is designed to be as easy as possible with a basic setup complete in few minutes.


There are many features available in the Flurry Analytics API, such as:

  • Session tracking
  • Event logging, with optional parameters
  • Page View tracking
  • Demographics tracking, such as age, gender and user id
  • Location tracking
  • App version tracking
  • And much more…

Getting Started

The setup for all the platforms is very easy with only a few steps:


  1. Add the INTERNET permission to AndroidManifest.xml.
  2. Add FlurryAgent.OnStartSession(this, "YOUR_API_KEY"); to the OnStart method of the Activity or Service.
  3. Add FlurryAgent.OnEndSession(this); to the OnStop method of the Activity or Service.


  1. Add FlurryAgent.StartSession("YOUR_API_KEY"); to the FinishedLaunching method of the Application Delegate

Windows Phone

  1. Add ID_CAP_NETWORKING and ID_CAP_IDENTITY_DEVICE capabilities to WMAppManifest.xml.
  2. Add FlurryWP8SDK.Api.StartSession("YOUR_API_KEY"); to Launching and Activated events of the Application.

And that’s it, your mobile app will start sending activity usage statistics to the Flurry servers!


Flurry Analytics SDK supported versions:

  • SDK for iOS supports Xcode tools 4.5 and above
  • SDK for Android supports Android API level 10 (Gingerbread) and above
  • SDK for Windows Phone supports Windows Phone 8 and above


The Flurry.Analytics API is available on (Flurry.Analytics) and on GitHub (mattleibow/Flurry.Analytics).

It is released under the same license as the native libraries.

The Making Of

You can read up on how the binding was created in my blog:

  1. Introduction and Pre-requisites
  2. Xamarin.iOS binding
  3. Xamarin.Android binding
  4. Flurry.Analytics in the wild

Bing Maps iOS SDK

The Bing Maps iOS SDK is a control for embedding maps directly into native iOS apps. With a rich, gesture-based UI, the SDK provides support for adding pushpins and other overlays to the maps. The SDK also allows your device location to be displayed and provides the ability to retrieve contextual information for a given map location.

This project provides a managed binding of the native library for Xamarin.iOS.

Sadly, after getting all this nice stuff going, I found the actual native library to be very buggy and often caused the app to crash. For example, if the push pins were animated, tapping them caused the app to crash. As a result, I won’t be pushing this to the stores.

Getting Started

Before you can use the map control, you will need a Bing Maps Key from the Bing Maps Portal. The process is described in the MSDN documentation, Getting a Bing Maps Key, and is very simple with only four steps.

A map key is not required for the maps to appear, but will display a popup reminder every time a map view is displayed.

Using the Map View

Once you have obtained a key, the next step is to add the map view to your app. You can obtain the control from the 3.

Once you have added the assembly to your app, you then need to add your Bing Maps Key to the Info.plist file in your project. This is a string key-value item with the key, BingMapsKey, with the value being the key you obtained from the portal.

Now, all that is left to do is to add the map view to your view. This can be done in the code or in the designers (storyboards or interface files).

If we are going to use the designers, then you can just add a UIView to your app, and then change the Class to be BMMapView. When the app is launched, a map should appear. If the code is used, then this snippet is all that is needed:

    // create the map view
    BMMapView mapView = new BMMapView (UIScreen.MainScreen.Bounds);
    // add to some View
    View.AddSubview (mapView);
    // show the user's location on the map (optional)
    mapView.ShowsUserLocation = true;

Binding Flurry Analytics with Xamarin

Over the last few days I have been creating a Xamarin.iOS and Xamarin.Android binding for Flurry Analytics SDKs. Flurry Analytics is a neat little library that allows for tracking of your app usage and various user stats.
And, because I really enjoyed my time doing this, I thought that I will share just a bit of the fun times and the not-so-fun times.

I have split this project up into four parts:

  1. Introduction and Pre-requisites
  2. Xamarin.iOS binding
  3. Xamarin.Android binding
  4. Flurry.Analytics in the wild


Before we start any coding, we need to get all our tools and files needed for the actual binding tasks.

I was using both Windows 8, with Visual Studio, and Mac OS X with Xamarin Studio. You can bind the Android library on either platform, but for iOS, it is easier to use the Mac. In this case, I will use the Mac for both iOS and Android.

Some of my very excellent sources for this process were the actual Xamarin documentation:

But, along with this info, there are just a few things that you may need. Firstly, it is good to update your Xamarin Studio to the latest stable release as this makes sure that all potential problems are minimized from the start.

Then, the next cool tool to get hold of is, Objective Sharpie, for binding iOS libraries. This tool is quite nifty for quickly generating the .NET interfaces from the Objective-C header files. It uses the header files not the actual compiled native library. The Xamarin docs on Objective Sharpie has a brief walkthrough on how to use the tool, so I will assume you know how to use it.

After we have all our tools ready to go, we need those SDKs from Flurry.

What I did was to create a free account by Flurry, and then created an Android and iOS Application using their dashboard. You have to have an application before they will let you download their SDKs. This step is pretty straight forward, so I won’t go into it here right now. Once you have created and downloaded the SDKs, you can extract them to a nice location for reference.

Now to get started with the real work…

But, as this is quite a long process, I will be splitting this article into this intro, the iOS binding and the Android binding. So, enjoy!

Binding Flurry Analytics with Xamarin.iOS

This week, I needed to use Flurry Analytics in my Xamarin.iOS and my Xamarin.Android apps, but there was no .NET SDK for these platforms. Flurry did provide a SDK for each platform, but it was the native libraries, which cannot be used directly in .NET. Given this, I decided to bind those native libraries using Xamarin.iOS and Xamarin.Android.

I have split this project up into four parts:

  1. Introduction and Pre-requisites
  2. Xamarin.iOS binding
  3. Xamarin.Android binding
  4. Flurry.Analytics in the wild

The first thing we are going to bind is the iOS SDK for Flurry Analytics. This task needs two things from the downloaded SDK:

  • [iOS-sdk-path]/Flurry-iOS-5.2.0/Flurry/Flurry.h
  • [OS-sdk-path]/Flurry-iOS-5.2.0/Flurry/libFlurry_5.2.0.a

Of course, the version numbers may change for later releases. The header file (.h) is going to be used to generate the .NET interfaces and enums. The library (.a) is going to be used in the project.

Just before we do the cool things, we should just create our C# solution for the Xamarin.iOS binding. Just create a new project/solution and select the “iOS Binding Project” template. For my project name I used Flurry.Analytics.iOS, but you could use anything.

The default project has a few files in it, we will have a look at each one in depth as we go through the binding steps:

  • ApiDefinition.cs (this is for the generated .NET interfaces from Objective Sharpie)
  • AssemblyInfo.cs (the usual assembly information attributes)
  • Extras.cs (this is for any additional changes that are needed for the bound types)
  • StructsAndEnums.cs (this is for any extra types that you wish to include in the final assembly)

Creating the Initial Binding

This step will involve using Objective Sharpie to get us started, but we will almost always have to go in and tweak a few things.

So, first things first, open Objective Sharpie and start the wizard. Select the Flurry.h header file, and I used the namespace Flurry.Analytics. After saving your file somewhere, we can start the tweaks. I don’t save the result into my solution as the amount of tweaks needed is high enough that I like to have a before and after file. Also, this library is very small. But, there is no reason why you couldn’t just save over the ApiDefinition.cs file in you project.

Before we start, here is a snippet from the Flurry.h file:

    // an enum
    typedef enum {
        FlurryLogLevelNone = 0,
    } FlurryLogLevel;

    // the main class
    @interface Flurry : NSObject {
    // ...
    + (void)setAppVersion:(NSString *)version;
    + (NSString *)getFlurryAgentVersion;
    + (void)startSession:(NSString *)apiKey;
    // ...

In this snippet of Objective-C goodness, there is an enum named FlurryLogLevel and an @interface named Flurry. This will translate into a C# enum and class respectively. It is also good to note that all the methods on this particular type will be static.

The generated C# for this snippet is:

    // the enum
    public enum FlurryLogLevel : [unmapped: unexposed: Elaborated] {
        None = 0,

    // the main class
    [BaseType (typeof (NSObject))]
    public partial interface Flurry {
        // ...
        [Static, Export ("appVersion")]
        [Verify ("ObjC method massaged into setter property", "Flurry/Flurry.h", Line = 61)]
        string AppVersion { set; }

        [Static, Export ("getFlurryAgentVersion")]
        [Verify ("ObjC method massaged into getter property", "Flurry/Flurry.h", Line = 80)]
        string GetFlurryAgentVersion { get; }

        [Static, Export ("startSession:")]
        void StartSession (string apiKey);
        // ...

As you can see, the generated file is similar, but not quite the same.

Tweaking the Generated Binding (ApiDefinition.cs)

After we generated our C# files, there are several things to note:

  • This code doesn’t compile at all
  • A good few of our methods are set to properties, especially note the setter-only ones
  • There is a [Verify(...)] attribute which doesn’t even exist
  • Some [Export] attributes have a value that ends in a colon (:), and others do not
  • The type is not a class but an interface
  • The base type is specified as a [BaseType] attribute
  • The enum has the item prefixes removed

This is quite a list here, but not all are bad. Objective Sharpie can’t generate perfect code as Objective-C is not C#, so there will always be human intervention. In these cases, it will generate what it thinks to be best and then let you know.

The [Verify] attribute is one way that Objective Sharpie lets you know that it changed something. In this instance, it is letting us know that it changed the setAppVersion method into a property. This is because usually there is both a getter and a setter method for a Objective-C property. But in this case, it is actually a method.

As you may note, these properties have a slightly different [Export] attribute in that these members don’t end in a colon. This is valid for Objective-C property setters, but as this is a method, we should add a colon back. It is also valid for methods that take parameters.

So, to fix those properties, remove the [Verify] attribute. We should also fix the exported name, and for the setter property, add the colon back in.

    [BaseType (typeof (NSObject), Name = "Flurry")]
    public partial interface FlurryAgent {

        [Static, Export ("setAppVersion:")]
        void SetAppVersion (string version);

        [Static, Export ("getFlurryAgentVersion")]
        string GetFlurryAgentVersion ();

        [Static, Export ("startSession:")]
        void StartSession (string apiKey);


As you can see here, I corrected the SetAppVersion write-only property by transforming it into a void method that exports to setAppVersion:. Note the full name and colon as this method takes a parameter.

Also, I needed to fix the GetFlurryAgentVersion read-only property by transforming it into a string method that exports to “getFlurryAgentVersion”. Note the lack of colon as this method takes no parameters.

And finally, I decided I wanted my final class to be called FlurryAgent to avoid confusion with the namespace as well as indicate that it was the Agent. In order to do this, All I needed to do was to rename the type and add the Name property in the attribute with a value of "Flurry".

The reason for adding this property is, after changing the type name, the binding no longer will be able to find the underlying Objective-C type. Usually the binding will use the default name if none is provided, the C# class name. After changing it, it no longer reflected the Objective-C type name, hence the new property.

Managing the Structures and Enumerations (StructsAndEnums.cs)

The last thing to fix, in the generated code, is the enum.

This is simple to do, just remove the strange attribute-like bit: [unmapped: unexposed: Elaborated].

One of the nice things of Objective Sharpie is that it removes the enum prefixes and just uses the relevant bits. For example the original item was FlurryLogLevelNone, but this is now just None.

The final enum looks like this after it has been moved to StructsAndEnums.cs:

    public enum FlurryLogLevel {
        None = 0,

So far, all our generated code has been moved into either, ApiDefinitions.cs (the class), or StructsAndEnums.cs (the enum). We are still not complete yet, but we are nearly there.

Additional Binding Code (Extras.cs)

Once we have the basic binding done, we can always extend what the native library provided with extra features. This is done by adding new source files to the project.

For example, if for some reason you need to add any extra bindings to the library, say to access a private member or even just to make the new API cleaner and more .NET-like.

For example you could do something like this:

    public partial class FlurryAgent : NSObject {
        public static void LogTimedEvent (string eventName, Action action) {
            try {
                FlurryAgent.LogEvent (eventName, true);
                action(); // do our task
            } catch {
                FlurryAgent.EndTimedEvent (eventName, null);

What is happening here is that I am adding a new method to the final .NET assembly. This method can make use of the methods in the API definition interface. In this particular example, I am adding a method that can take an Actionand make sure that we fire a ‘starting’ and then an ‘ending’ event to the Flurry servers. This is a new bit of functionality that can be baked right into the binding assembly.

Working with the Native Library (.a)

This step is actually quite easy, just add the native library (.a) to the project, and you are almost done.

When you add the native library to the project, Xamarin Studio will create a new .linkwith.cs file that matches the library name. For example with Flurry, I added the libFlurry_5.2.0.a library to my project and it generated a libFlurry_5.2.0.linkwith.cs.

This new file is the last bit that needs to be done. It is for the linker when using this library in an iOS app. It usually will contain only a single line, a single [LinkWith] attribute. This attribute allows you to specify what targets this library can be used with, what extra iOS frameworks are needed, etc:

    [assembly: LinkWith (
        LinkTarget.Simulator | LinkTarget.ArmV6 | LinkTarget.ArmV7 | LinkTarget.ArmV7s, 
        ForceLoad = true)]

This is the default line, split for readability, and usually it is all that is needed. What this does is say that the linker must use the libFlurry_5.2.0.a native library as well as this library can be used on the Simulator and all the devices. The ForceLoad is used by the Xamarin.iOS linker, and specifies a linker flag. According to the documentation, this should always be true for now.

But just before we finish up, we need to add any required frameworks. Without this, there will be strange happenings…but different depending the configuration.

If building for Debug, the app will launch, but nothing will happen at all. The methods can be called and everything, but no actions will take place.

If building for Release, the linker will throw an error:

Error MT5211: Native linking failed, undefined Objective-C class: _OBJC_CLASS_\$_Flurry.
If ‘_OBJC_CLASS_\$_Flurry’ is a protocol from a third-party binding, please check that it has the [Protocol] attribute in its api definition file, otherwise verify that all the necessary frameworks have been referenced and native libraries are properly linked in.

This error is giving us lots of information for @protocol, but as we don’t have any in our project (recall the @interface), we can safely ignore the first part of the second message and focus on the ‘frameworks’ part. According to the Flurry documentation, the Security.framework is required and the SystemConfiguration.framework is optional, but recommended.

So, I added both frameworks, using the Frameworksproperty:

    [assembly: LinkWith (
        LinkTarget.Simulator | LinkTarget.ArmV6 | LinkTarget.ArmV7 | LinkTarget.ArmV7s, 
        ForceLoad = true, 
        Frameworks = "SystemConfiguration Security")]

As shown here, the frameworks are space-separated and do not have the .framework extensions.

Finishing Up

So far we have defined our API, added any additional logic or types, added the native library, set up the linker and specified the frameworks. This is all that is needed, so our library should build fine now and we should be able to use it in an Xamarin.iOS app:

    // the methods

    // the properties that we changed back into methods
    FlurryAgent.GetFlurryAgentVersion ();

    // the extra method that we added
    FlurryAgent.LogTimedEvent ("started", () => {
        // ...

Under the Hood

One thing to know is that the iOS binding project is actually not really compiled directly, but are a series of stages. Each file actually has a different build action.

The first stage to building the binding is to build a reference assembly with the files:

  • ApiDefinition.cs (with build action ObjcBindingApiDefinition)
  • StructsAndEnums.cs (with build action ObjcBindingCoreSource)

Next, this assembly is then reflected to generate the actual binding code. This generated code is then compiled with the rest of the files:

  • Extras.cs (with build action Compile)
  • StructsAndEnums.cs (again with build action ObjcBindingCoreSource)
  • libFlurry_5.2.0.linkwith.cs (with build action Compile)
  • libFlurry_5.2.0.a (with build action ObjcBindingNativeLibrary but is actually just a resource)

An example of the generated code in the second stage, the interface member void StartSession(string) is actually used to generate a big block of code:

    [Export ("startSession:")]
    public static void StartSession (string apiKey)
        if (apiKey == null)
            throw new ArgumentNullException ("apiKey");
        var nsapiKey = NSString.CreateNative (apiKey);

        MonoTouch.ObjCRuntime.Messaging.void_objc_msgSend_IntPtr (class_ptr, selStartSession_Handle, nsapiKey);
        NSString.ReleaseNative (nsapiKey);

This is all the magic that happens under the hood to redirect values from the managed .NET to the underlying native library.