An iOS Inspector that runs inside your app, so you can debug and analyze from your device in real-world situations.
Latest commit 0e21a64 Apr 19, 2014 @colinta docs
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Developer tools for iOS. Runs on the device, no browser or computer needed.

(think Firebug or Webkit Developer Tools)


  1. gem install motion-xray
  2. Replace UIWindow with Motion::Xray::XrayWindow

And if you want the email features, add app.frameworks << 'MessageUI' to your Rakefile.

The Problem

During development we rely heavily on the simulator to quickly view and test features, but often when we finally install our app on a device, the experience is not up-to-snuff with what was going on in the simulator. Views are off by a few pixels, performance is not what we expect, and crashes occur where we never saw them in the simulator. Sometimes these are device problems, sometimes it has to do with dropping in and out of signal, all sorts of scenarios that we cannot easily test for in the simulator.

And of course there is the problem that iOS devices have more features than the simulator! Bluetooth 4, for example, is not easy to get setup in the simulator (and you have to buy a USB bluetooth module).

My thesis is that we need to make on-device testing a more enjoyable and useful testing environment, so that we are compelled to test on it sooner and more often.

My Proposal

Motion-Xray is such a solution. During development you can use Xray as a UI inspector, or to monitor the console log, preview how accessibile your app is (to blind and color blind developers), or you can create a plugin that provides information specifically useful to your app. Below I'll show how to create a new plugin. Check out the plugins folder for some examples.


If you clone and run Xray in the simulator, you will see a very boring app:

Xray Screenshot

Activate a "shake" gesture by pressing ⌘⌃Z and Xray will activate, which displays this:

Xray Screenshot

The application shrinks down to a quarter size, and the development environment takes up the remaining space. That is Xray, an in-app debugging and development environment! 😃


That's enough to have the Motion::Xray.toggle command fired whenever you shake the device. If you want to use some other mechanism that launches Xray (a complicated gesture recognizer would be a good candidate), you can call Xray.toggle (which calls either Xray.fire_up or Xray.cool_down). The Motion::Xray::XrayWindow class is only used to listen for the shake event, so using it will not affect your app in any other way.

When you shake your phone and activate Xray, you are presented with three panes and a toolbar at the bottom:

Preview panes

1. Preview

All the views under the main window are placed in the Preview area:

Preview pane

If you touch this area, you can get a quick preview of the view, or you can quickly change to another view, or change orientation. After a few seconds, Xray will automatically be displayed again. If you want to leave the Xray debug area, you should shake the phone again.

2. UI Selector

This pane shows the view hierarchy of your app:

UI selector pane

All the views on screen can be selected here, and a red box will show the bounds of that view in the Preview pane. If you touch it again, that view will be sent to whatever plugin you have visible, or you can press the "down" button in the bottom-right corner of this pane.

Not all plugins respond to the selected view. For instance the accessibility plugin will always display the entire screen, regardless of which view is selected. The log plugin, on the other hand, displays the inspect information about the view. And of course the UI plugin will change so that you can edit the properties of that view.

The button in the upper-left corner expands this view, so that you can see the tree easier.

Expanded tree view

In the upper-right corner is the button to activate a visual view selector:

UIView selector

You can tap a view to get information about it, or press and hold to make that view "go away" so that you can choose the view behind it, or double-tap to select that view.

3. Plugin Canvas

Here's where the inspector and other plugins live, with a toolbar at the bottom to select what plugin you want to view:

Plugin pane

It is very easy to create new plugins, I'll go over that below. After you create a new plugin, you register it with Xray:


Built-in plugins

UI (Motion::Xray::UIPlugin)

included automatically

The original idea for Xray was just this UI plugin. The other plugins came later. I realized that it could (and should) be a generic "development environment" instead of a "UI editor". Also, some early feedback from the HipByte team helped open up this world of possibilities. :-)

UIPlugin uses a pluggable architecture. First, there are the editors:

  • Motion::Xray::TextEditor
  • Motion::Xray::ColorEditor
  • Motion::Xray::BooleanEditor
  • Motion::Xray::FrameEditor

Second, these editors get associated with the view properties in a Hash that is returned by the class method UIView##xray. In custom views you only need to return the properties that your custom view uses; any editable properties in views you inherit from will be included. Don't do any merging in your xray method, that is handled by the plugin (by UIView##build_xray, in xray_ext.rb)

class << UILabel
  def xray
      'Content': {  # section name
        text: Motion::Xray::TextEditor,  # property => editor class

If you inherit from a view and you want to disable one of the editors, assign nil as the editor for that property. UIWindow does this to prevent editing frame, hidden, and userInteractionEnabled properties from getting changed.

class << UIWindow
  def xray
      'TurnOff' => {
        frame: nil,
        hidden: nil,
        userInteractionEnabled: nil,

Writing custom editors can be time consuming, because they are often very UI heavy (check out the ColorEditor to see what I mean). That said, the concept is very easy:

  1. extend the Motion::Xray::PropertyEditor class.

  2. Return your editor in the edit_view(container_width) method. You don't have to use the entire width, but your editor view can't be any wider.

    If you want, you can return a "preview" that just shows the value, with a button that opens a much larger editor. ColorEditor and TextEditor behave this way.

  3. To get the value of the property being edited, use the method get_value. It will introspect looking for a the appropriate getter method.

  4. Whenever the value changes, assign the new value to set_value, and that will fire a XrayTargetDidChangeNotification notification, which is used by Motion::Xray::SaveUIPlugin. set_value will, like get_value, look for an appropriate setter.

The editors should be able to be used for many properties, but if you're writing a one-off editor, I suppose you could call the getters and setters directly, but you should post the XrayTargetDidChangeNotification notification if you do this.

Save UI (Motion::Xray::SaveUIPlugin)

After you have made your changes to your UIViews, you will want to save those changes, right? This plugin is your friend. It is not included by default, though, because not everyone uses teacup or pixate.

Many of the properties that you'll be editing will already have the appropriate output in this plugin (it uses #inspect), but the way that Xray records your changes can be customized in two ways:

  1. Change the type of output that you want. The default is teacup, but it is possible to setup the SaveUIPlugin to record NUI or Pixate changes as well.

    Motion::Xray.registerPlugin(  # use teacup
  2. Register custom output, by class. This will be used for any property, for instance if you want UIColor objects to be persisted as an array of RGB values, you could register that output like this:

    register(:teacup, UIColor) { |color| "[#{}, #{}, #{}]" }

Because Xray uses SugarCube, a lot of the hard work is done for us there (because SugarCube implements lots of useful to_s and inspect methods)

Accessibility (Motion::Xray::AccessibilityPlugin)

included automatically

This plugin provides two screenshots of the current screen. One that mimics how a sightless person would "see" your app, and another that mimics how a (very) color blind person would see it. Each one is at best, an approximation, but the goal is that having this quick metric handy will encourage more developers to spend some time on accessibility. A little goes a long way!

Accessibility Plugin

This plugin generated a lot of excitement when I announced Xray at the RubyMotion conference, #inspect2013. We had all heard [Austin Seraphin's][austinseraphin] talk the previous day, about how to improve accessibility. This plugin tries to provide a visualization of the recommendations he gave us - first and foremost, he recommended that you should at least set the accessibilityLabel on custom views.

The left side shows a screenshot of your app with only red and green squares. Green squares mean "you're doing OK". It does NOT mean that your app has "good" accessibility, but at a minimum you should at least get all your screens "in the green" before you send your app to an accessibility consultant.

The other screenshot is a your app in black and white, with colors desaturated. An attempt to mimic how a color blind person would see your app. There are many types of color blindness, and down the road I would love to see a few different screen shots for each specific type in this pane. For now, it takes the "common denominator" approach, which is to remove all color.

Log (Motion::Xray::LogPlugin)

included automatically

Log Plugin

This plugin requires more involvement in your application code, if you want to make it useful. You basically need to use the Motion::Xray::Log.log family of methods, and each of them will write to the Motion::Xray::LogPlugin.log buffer. Here's a quick way to do this:

Log = Motion::Xray::Log'info!')
Log.error('an error occurred!')
# available methods:
#   Log.error, Log.warning, Log.log, Log.notice,, Log.ok, Log.debug

# only log information greater than or equal to log level "warning"
Log.level = Log::Warning

Or you can write a log method yourself that calls one of the Motion::Xray::Log methods. If you use CocoaLumberjack, it should be very easy to hook up Motion::Xray::Log, but it will have to be done in Obj-C I think (I took a stab at it, but gave up when I couldn't access the message property).

The upside to using these Motion::Xray::Log methods is that they use pretty coloring, they output to both the console and the Xray log, and I'm planning on including some awesome-print-like features to the log methods in the future (or, more likely, delegate to awesome-print if it's available).

Writing an Xray plugin

My hope is that you will identify places in your app where you would benefit from on-device feedback. Here are just some ideas as examples:

  1. Building an app that interacts with bluetooth devices: How about signal strength? Devices detected? Connect and disconnect buttons?
  2. Interfacing with an API: Logging requests, logging parameters sent and responses, interface to send arbitrary requests
  3. Building a game: framerate, number of textures on screen. To find out when the performance breaks down on the device, you can't trust the simulator!

So, let's get to it. I will use some code from AccessibilityPlugin in this example.

First, the most basic plugin structure:

class AccessibilityPlugin < Plugin
  name 'Accessibility'  # as you want it to appear in the toolbar

  # canvas is the view where the plugin will be placed.  You do not need to
  # call `addSubview` on this object.
  def plugin_view(canvas)
    return UIView.initWithFrame(canvas.bounds)


So far we have:

  • named our plugin 'Accessibility'
  • returned an empty container

Let's add our two image views. We'll make use of geomotion, which is required by Xray:

def plugin_view(canvas)
  return UIView.alloc.initWithFrame(canvas.bounds).tap do |view|
    view.backgroundColor = :black.uicolor

    @accessibility = UIButton.alloc.initWithFrame(view.bounds
      .thinner(view.bounds.width / 2))
    @colorblind = UIButton.alloc.initWithFrame(view.bounds
      .thinner(view.bounds.width / 2)
      .right(view.bounds.width / 2))

    view << @accessibility
    view << @colorblind

When the plugin is activated, we should grab a screenshot of the app and assign it to each view. The show method is called on a plugin when it is selected.

def show
  Dispatch::Queue.main.async do
    @colorblind.setImage(get_colorblind_image, forState: :normal.uicontrolstate)
  Dispatch::Queue.main.async do
    @accessibility.setImage(get_accessibility_image, forState: :normal.uicontrolstate)

The AccessibilityPlugin does a few more things like show spinners, display a big screenshot image on touch, and I haven't implemented the get_{accessibility,colorblind}_image methods here, but hopefully this is enough for you to get the gist of writing a plugin. Here is the entire list of methods that you can call, or get called, on a plugin:


  • name - the name as it appears in the toolbar
  • view - stores the plugin view that is returned by plugin_view. This method is only created once (much like UIViewController#loadView)
  • target - the view that has been selected in the UI picker

Methods you must implement

  • plugin_view(canvas_view) - the view returned by this method will be placed in canvas_view when your plugin is selected

Methods you can implement

  • edit(target) - called when a new view is chosen in the UI picker. You should call super, which assigns this view to the target property. Then you can update self.view with any changes that you need to apply.
  • show - called when your plugin is selected (this will always be after edit(target))
  • hide - called just before your plugin is removed from the canvas

Registering your plugin

Register your new plugin in the AppDelegate#application(didFinishLaunchingWithOptions:) method.

class AppDelegate
  def application(application, didFinishLaunchingWithOptions:launchOptions)
    @window = Motion::Xray::XrayWindow.alloc.initWithFrame(UIScreen.mainScreen.bounds)

    # include the SaveUIPlugin, which is not included by default

    # include a custom plugin

    return true


Xray depends on geomotion, which I don't feel bad about, and SugarCube. I would consider removing the SugarCube dependency, because not everyone uses it, but SugarCube adds a ton of benefit (like #to_s and UIColor additions).