First, download and install Objective Sharpie from http://tinyurl.com/ObjectiveSharpie, then perform the following steps:

You should have not received any error messages from Objective Sharpie during the process, and when finished, your screen should look like the following screenshot:

Now if you return to your binding project, you'll notice that Objective Sharpie has generated an interface definition for every class discovered in the header files of the library. It has also generated many enum values that the library uses and changed casing and naming conventions to follow C# more closely where possible.

As you read through the binding, you'll notice several C# attributes that define different aspects about the Objective-C library such as the following:

The only other rule to know is how to define constructors. Xamarin had to invent a convention for this since C# interfaces do not support constructors.

To define a constructor besides the default one, use the following code:

[Export("initWithFrame:")]
IntPtr Constructor(RectangleF frame);

This would define a constructor on the class that takes in RectangleF as a parameter. The method name Constructor and the return type IntPtr signal the Xamarin compiler to generate a constructor.

Now, let's return to our binding project to finish setting up everything. If you compile the project at this point, you'll get a few compiler errors. Let's fix them one by one as follows:

One more error remains regarding Objective Sharpie not being able to generate C# delegates for methods that have callbacks. Navigate to the GAI interface and change the following method:

[Export ("dispatchWithCompletionHandler:")]void DispatchWithCompletionHandler (
    GAIDispatchResultHandler completionHandler);

You will also need to define the following delegate at the top of this file:

public delegate void GAIDispatchResultHandler(
    GAIDispatchResult result);

After going through these issues, you should be able to compile the binding and get no errors. You could have read the Objective-C header files and written the definitions yourself by hand; however, using Objective Sharpie generally means a lot less work.

At this point, if you try to use the library in an iOS project, you would get an error such as the following:

Error MT5210: Native linking failed, undefined symbol: 
    _FooBar. Please verify that all the necessary frameworks 
    have been referenced and native libraries are properly 
    linked in.

We need to define the other frameworks and libraries that the Objective-C library uses. This is very similar to how references work in C#. If we review the Google Analytics documentation, it says that you must add CoreData, SystemConfiguration, and libz.dylib. Additionally, you must add a weak reference to AdSupport.

Open libGoogleAnalyticsServices.linkwith.cs that was created automatically nested underneath the *.a file and make the following changes:

[assembly: LinkWith ("libGoogleAnalyticsServices.a",
  LinkTarget.ArmV7 | LinkTarget.ArmV7s | LinkTarget.Simulator,
  LinkerFlags = "-lz",
  Frameworks = "CoreData SystemConfiguration",
  WeakFrameworks = "AdSupport",
  ForceLoad = true)]

We added references to frameworks in the following ways:

After these changes are implemented, you will be able to successfully use the library from iOS projects. For complete documentation on Objective-C bindings, visit the Xamarin documentation site at http://docs.xamarin.com/ios.