Expose iOS and OS X system libraries in RubyMotion.

Outside of the usual Apple frameworks, iOS and OS X include many system libraries, with the most well known examples being SQLite, and Libxml2. RubyMotion provides the ability to directly call into C libraries through a mechanism called BridgeSupport, which takes us to the point in the story where motion.h is introduced. In order to use BridgeSupport, the compiler must be fed an XML file that describes a library's C API, and this is what motion.h takes care of. Simply declare the header files needed, just like in C, and now RubyMotion code can call directly into the specified system library, without having to write an Objective-C wrapper.

Note, BridgeSupport only supports C libraries, C++ support does not exist.

RubyMotion's Runtime Guide includes a section called Interfacing with C, which is a must read for learning how to interact with C libraries in RubyMotion.

Add this line to your application's Gemfile:

gem 'motion.h'

And then execute:

$ bundle

Or install it yourself as:

$ gem install motion.h

In the Rakefile:

Motion::Project::App.setup do |config|
  config.libs << '/usr/lib/libsqlite3.dylib'
  config.include 'sqlite3.h'
end

Example: Creating an in-memory database:

dbptr_out = Pointer.new(Sqlite3.type) # => sqlite3 **
sqlite3_open(':memory:', dbptr_out)
dbptr = dbptr_out.value # => sqlite3 *
sqlite3_exec(dbptr, 'create table gems (name text)', nil, nil, nil)
sqlite3_exec(dbptr, 'insert into gems values ("motion.h")', nil, nil, nil)
callback = ->(_context, count, values_array_ptr, column_names_array_ptr) {
  count.times do |column_number|
    column_name = column_names_array_ptr[column_number]
    value = values_array_ptr[column_number]
    puts "#{column_name}: #{value.inspect}"
  end
  0 # sqlite3_exec requires 0 to continue
}
sqlite3_exec(dbptr, 'select * from gems', callback, nil, nil)

In the Rakefile:

Motion::Project::App.setup do |config|
  config.include 'objc/runtime.h'
end

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request