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An open journal-- some of it written for you, but most of it is for me.

RubyMotion Day 1

Course Goals

  • Objective-c Conventions
  • Using C Libraries
  • Platform Idioms
  • Key concepts: pointers, memory management, objects, messages
  • Fundamental iOS libraries
  • Cocoa patterns
  • Testing

History of why Objective-C

  • NeXt
    • used objective-c to write the main platform
      • there was a debate on which was better between objective-c and c++, C++ eventually won
    • If you wanted to write an application on NeXt you needed to use NeXt builder
    • OSX was built next and there are a lot of things in OSX that were inherited from NeXt
  • iOS is basically a version of OS10

iOS Overview

  • The window server and Cocoa send events and messages to each other. It is a two way communication.
  • each application has its own loop of communication. Responsible for send and receiving events from the window server.

  • For each object in the nib file

    • Class is sent alloc to create interface
    • New instance is sent init
    • Instance variables are set

Application States

  • Two states: foreground and background
    • two states for foreground: inactive and active
    • in the background: you can do tasks in the background, after it is done it will go to suspended


  • UIkit is the main library that comes with cocoa and certainly the most important.

App delegate

  • There are at least two classes. The application class and the application delegate.

Create a new project

motion create <app name>

  • fonts, images, assets all go in the resources folder


  • rake -T gives me a list of all the rake tasks
    • can build for a device or build for the simulator
  • can create a static library with rake static
  • rake config gives you output on the frameworks, delegate_class, etc.
    • CoreGraphics lib is what we use for animation

Deploying the application

  • need an apple certificate and developer certificate

To see the UI structure

UIApplication.sharedApplication.keyWindow.recursiveDescription -> this will give you the tree structure of what you have created.

Changing attributes in the console

self.font = UIFont.fontWithName("Noteworthy-Bold",size:18) will change the font of the label that you have highlighted.

Object C

  • objective-c is an objected oriented flavor of c
  • heavily influenced from Smalltalk language
  • all keywords begin with @

  • RubyMotion adds named parameters similar to Ruby 2.0

  • Both Ruby and Objective C has the notion of open classes, single inheritance and single message dispatch

now dateByAddingTimeInterval:1000, structure is the receiver theSelector:argument

  • messages always enclose the receiver and the selector inside a pair of square brackets. These brackets can be nested.
  • id is a pointer to any object type.

  • you can invoke objective-c OR ruby methods against built in classes

  • [1,2,3].send(:objectAtIndex, 1) -> you need the colon or it won’t find the selector!
  • helpful to use short methods and callbacks because the method will not be released until it is terminated.

Objective C Classes

  • NSString (similar to when you freeze something in Ruby) v. NSMutableString
  • NSSArray v. NSMutableArray
  • NSSet v. NSMutableSet
  • NSDictionary v. NSMutableDictionary

  • my_string = "hello" -> this is mutable

  • my_stgring = NSString.alloc.init -> this is immutable


  • NSArray is immutable. Once you create one it can’t be modified. NSMutableArray is a mutable subclass of NSArray
    • need to terminate a NSArray.arrayWithObjects(foo, bar, baz, nil) with a nil or it will crash.


  • Sets are collections with no order and objects can be present only once (can only be added once).It is useful when dealing with membership issues.
  • .unionSet, .intersectSet


  • Dictionaries are unordered and associate a key.


  • in objective c -> constants usually start with k -> kItemCode
  • in Ruby make sure that this is uppercase -> KItemCode

Defining a class

  • Obj c uses the keyword @interface to define the class
  • Obj c only supports single inheritance. You can only inherit from one superclass at a time.


  • similar to the concept of interfaces in java or C-sharp
  • a protocol is a contract. It is a promise to the compiler that a given class will implement a given interface.


  • the way to add methods to an existing class


  • C structures are mapped to classes in RubyMotion. CGPoint is very common.
  • It is possible to pass the field views directly to the constructor `pt= CGPoint.new(100,200)


  • Pointers are basic data types of the C language
  • RubyMotion supports the creation o structure pointers, by passing their runtime type accordingly to Pointer.new


  • The caret () character is used to define C blocks
  • The Prob object must have the same number of args as the C function pointer or block, otherwise an exception will be raised at runtime

Keyboard doesn’t toggle by default

  • Add this code
  def textFieldShouldReturn(textfield)
    return false

Setting a title of a button


List of wrappers