MonoTouch BTouch Binding Sample

This example shows how we can utilize an existing Objective-C library and expose it for use in a MonoTouch project. For instance, you may have existing code written in Objective-C that you may want to bind to C# to consume in your MonoTouch project. This sample provides a basic template/overview of the steps involved, including:

• Creating a "fat" or multi-architecture library that can be target both the iOS simulator and device.
• Defining an API definition file in the form of a C# interface against the Objective-C API.
• Building a *.dll that contains both the binding and and the embedded native library.

Understanding this Sample

This sample consists of three distinct source projects:

• Xcode Project in Objective-C
• MonoTouch Binding classes
• MonoTouch Sample Project

Please see the README in each project folder for more details.

Building this Sample

To compile the Xcode Project and binding classes execute the make command from the root directory.

The make command will:

• Compile the XCode Project for ARM6, ARM7, and Simulator
• Create a multi-architecture binary using lipo
• Create a *.dll in the binding folder using btouch

The resulting .dll is created using the [LinkWithAttribute] (http://docs.xamarin.com/ios/advanced_topics/binding_objective-c_types#Linking_the_Dependencies) and will automatically embed the native library in your application.

Creating a Universal Binary

A "fat" or multi-architecture library is a compiled binary that is usable on multiple targets, for example: armv6, armv7, i386 (simulator). In this sample we illustrate how to create a universal binary in two ways:

Using lipo

Once we have built our library against the desired architectures we can create the universal binary via lipo. This will create a "universal" file from the architecture specific inputs we have provided. For instance:

lipo -create libXMBindingLibrarySample-armv7.a libXMBindingLibrarySample-armv6.a libXMBindingLibrarySample-i386.a -output libXMBindingLibrarySampleUniversal.a

Similarly, in our Makefile script we have lipo -create -output $@ $^ which will take the libraries compiled for armv6, armv7, and i386 using xbuild and output them to the current directory with the name of our build target.

Using Xcode

In our Xcode project we have created a separate Build Target that will execute a post build Run Script to output a "universal" file.

This Run Script is also available for reference in the "Post-Build Run Script" group of the Xcode project.