awesome_print_motion for RubyMotion

The Problem

Let’s say we’re building a version of Atari’s Pong in RubyMotion. We’re debugging an issue with the paddles; they don’t line up the way we want them to. Time to examine the playing field via the RubyMotion console.

pong-rm $ rake

Mouse over the playing field and Command-click to grab the entire playing field object in the RubyMotion console. Confirm that you grabbed the object by typing self at the console prompt.

(UIView(#9d820c0, [[0.0, 0.0], ...)> self

=> UIView(#9d820c0, [[0.0, 0.0], [480.0, 320.0]]), child of UIView(#c876920)

And then, to see what objects are on the playing field, use self.subviews to show the subviews array of the current object.

(UIView(#9d820c0, [[0.0, 0.0], ...)> self.subviews
=> [UIView(#9d82430, [[357.0, 175.0], [50.0, 50.0]]), child of
UIView(#9d820c0), PaddleView(#9d82580, [[410.0, 190.0], [20.0, 100.0]]),
child of UIView(#9d820c0), PaddleView(#9d82970, [[10.0, 190.0], [20.0,
100.0]]), child of UIView(#9d820c0), ScoreLabel(#9d82a80, [[110.0, 9.0],
[20.0, 42.0]], text: "1"), child of UIView(#9d820c0),
ScoreLabel(#9d83c90, [[350.0, 9.0], [20.0, 42.0]], text: "0"), child of
UIView(#9d820c0)]
(UIView(#9d820c0, [[0.0, 0.0], ...)>

This blob of text is difficult for the human brain to parse.

Solution: awesome_print_motion

Now, let’s try it with the awesome_print_motion gem.

(UIView(#9d820c0, [[0.0, 0.0], ...)> ap(self.subviews)
[
    [0] UIView(#9d82430, [[308.0, 118.0], [50.0, 50.0]]), child of UIView(#9d820c0),
    [1] PaddleView(#9d82580, [[410.0, 190.0], [20.0, 100.0]]), child of UIView(#9d820c0),
    [2] PaddleView(#9d82970, [[10.0, 190.0], [20.0, 100.0]]), child of UIView(#9d820c0),
    [3] ScoreLabel(#9d82a80, [[110.0, 9.0], [39.0, 42.0]], text: "61"), child of UIView(#9d820c0),
    [4] ScoreLabel(#9d83c90, [[350.0, 9.0], [20.0, 42.0]], text: "0"), child of UIView(#9d820c0)
]
=> nil
(UIView(#9d820c0, [[0.0, 0.0], ...)>

Much easier to read. The structure of the subviews array is clear. Each element of the array has an easy-to-read index. Debugging time is reduced.

How to Install awesome_print_motion

RubyMotion uses bundler. So we start by refering to awesome_print_motion in our gemfile.

gem 'awesome_print_motion'

In the app’s Rakefile, there are two possible ways to proceed. The preferred way is to use the following lines to tell the app to require every gem mentioned in Bundler’s Gemfile:

begin
  require 'bundler'
  Bundler.require
rescue LoadError
end

The older way is to manually add a require statement to the Rakefile.

require 'ap'

Personally, I prefer the newer way because it automatically requires all of the gems mentioned in the Gemfile. The odds of a typo-induced error are reduced.

How to Use awesome_print_motion

To use the new gem, start the app and explore away. Any time you want to run output through the awesome_print_motion gem, send the code as a parameter to the ap method like so…

> ap(self.subviews)

… and the output will be easier to read.

Acknowledgements

Thank you Michael Dvorkin for adding RubyMotion support to your awesome_print gem.