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Updating Xamarin.Mac Unified applications to 64-bit

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As of January 2018, Apple requires that new Mac App Store submissions target 64-bit. Apps already available on the Mac App Store must be updated to target 64-bit by June 2018.

The File > New Xamarin.Mac project template creates 64-bit applications by default, so any recently created apps are already 64-bit compatible and will not require any changes.

Targeting 64-bit

  1. Open the Project Options window for your Xamarin.Mac app:

    The contextual menu for the project

  2. Select Mac Build and set Supported architectures to x86_64:

    Setting the supported architectures to x86_64

  3. If your app has any external dependencies such as native references or binding projects, update them to target 64-bit.

Errors

The first time you build or run your application with 64-bit support, you may encounter link errors from clang or runtime issues. These errors can occur if third-party dependencies — for example, native references in your Xamarin.Mac or bindings projects, or manually-loaded system-wide frameworks — have not been updated to 64-bit.

Tip

Converting your project to 64-bit is a major change and may indirectly uncover various programming errors. In particular it may change the size and alignment of data structures, which would affect p/invoke signatures and native code linked in your project. Consider reviewing any build warnings given and test your application thoroughly afterwards to catch potential issues.

Example error resulting from a dynamically-linked third-party dependency that does not target 64-bit:

ld : warning : ignoring file PATH/ThirdPartyLibrary.framework/ThirdPartyLibrary, 
file was built for i386 which is not the architecture being linked (x86_64): 
PATH/ThirdPartyLibrary.framework/ThirdPartyLibrary

This error could be followed at runtime by dlopen returning IntPtr.Zero instead of an expected handle.

Example error resulting from a statically-linked third-party dependency that does not target 64-bit:

Undefined symbols for architecture x86_64:
  "_LibraryFunction", referenced from:
     -u command line option
ld: symbol(s) not found for architecture x86_64

To build and run successfully, update these dependencies to 64-bit and recompile your app.