iOS Switch on change action

  • code, ruby, rubymotion, ios, formotion, technical

rubymotion logo I’ve been using RubyMotion recently to build an iOS app for a client. It’s really good fun!
It turns out that there’s an easy way to perform actions, such as saving, when toggling a switch in RubyMotion. I’m using Formotion but the same approach should work without it.

There’s no on_change callback on the switch field so I had to find another solution. RubyMotion BubbleWrap’s Observers is the way I sorted it. You have to include the BW::KVO module which gives you the ‘observe’ function. This takes the object to observe, the param to observe and a callback block.

Something like this:

class SwitchOnChangeScreen < PM::FormotionScreen
  include BW::KVO

  def on_load
    sync_over_3g = self.form.sections[0].rows[0] # TODO change this, error prone
    observe(sync_over_3g, "value") do |old_val, val|
      # save new val
      App.alert(val ? "Yes" : "No")

  def table_data
      sections: [{
        title: "Network",
        rows: [{
          title: "Sync over 3G",
          key: :sync_over_3g,
          type: :switch,
          value: false

The result:

switch on change preview