navigation.rb

class UI::Navigation
  attr_reader :root_screen

  #In pixels
  def self.bar_height
    @bar_height ||= begin
      value = Android::Util::TypedValue.new
      if UI.context.theme.resolveAttribute(Android::R::Attr::ActionBarSize, value, true)
        Android::Util::TypedValue.complexToDimensionPixelSize(value.data, UI::context.resources.displayMetrics)
      else
        resource_id = UI.context.resources.getIdentifier('action_bar_default_height', 'dimen', 'android')
        if resource_id
          UI.context.resources.getDimensionPixelSize(resource_id)
        else
          0
        end
      end
    end
  end

  def initialize(root_screen)
    @root_screen = root_screen
    @root_screen.navigation = self
    @current_screens = [@root_screen]
  end

  def screen
    @current_screens.last
  end

  def hide_bar
    bar = UI.context.supportActionBar
    if bar.isShowing
      bar.hide
      Task.after 0.05 do
        bar_height = bar.height>0 ? bar.height : self.class.bar_height
        @current_screens.each do |e|
          e.view.height += (bar_height / UI.density)
          e.view.update_layout
        end
      end
    end
  end

  def show_bar
    bar = UI.context.supportActionBar
    if !bar.isShowing
      bar.show
      Task.after 0.05 do
        bar_height = bar.height>0 ? bar.height : self.class.bar_height
        @current_screens.each do |e|
          e.view.height -= (bar_height / UI.density)
          e.view.update_layout
        end
      end
    end
  end

  def title=(title)
    UI.context.supportActionBar.title = title
  end

  def bar_color=(color)
    UI.context.supportActionBar.backgroundDrawable = Android::Graphics::Drawable::ColorDrawable.new(UI::Color(color).proxy)
  end

  def items=(items)
    fragment = @current_screens.last.proxy

    has_menu = false
    has_menu |= (fragment._buttons = items[:buttons])
    has_menu |= (fragment._options_menu_items = items[:options_menu_items])
    has_menu |= (UI.context.supportActionBar.displayHomeAsUpEnabled = (items[:home_button_enabled] or false))
    fragment.hasOptionsMenu = has_menu
  end

  def push(screen, animated=true)
    @stack_change_reason = :push
    screen.navigation = self

    fragment = screen.proxy
    fragment._animate = animated ? :slide : false

    current_fragment = @current_screens.last.proxy
    current_fragment._animate = animated ? :fade : false

    transaction = proxy.beginTransaction
    transaction.hide(current_fragment)
    transaction.add(UI.context.findViewById(Android::R::Id::Content).id, fragment, nil)
    transaction.addToBackStack(nil)
    transaction.commitAllowingStateLoss

    @current_screens << screen
  end

  def pop(animated=true)
    if @current_screens.size > 1
      @stack_change_reason = :pop
      current_screen = @current_screens.pop
      current_screen.proxy._animate = animated ? :slide : false
      previous_screen = @current_screens.last
      previous_screen.proxy._animate = animated ? :fade : false

      previous_screen.before_on_show
      proxy.popBackStack
      previous_screen.on_show

      current_screen
    else
      nil
    end
  end

  def proxy
    @proxy ||= begin
      manager = UI.context.fragmentManager
      manager.addOnBackStackChangedListener(FlowFragmentManagerStackChangedListener.new(self))
      manager
    end
  end

  def stack_changed
    case @stack_change_reason
    when :push
    when :pop
    else
      @current_screens.pop
      previous_screen = @current_screens.last
      if previous_screen
        previous_screen.before_on_show
        previous_screen.on_show
      end
    end
    @stack_change_reason = nil
  end
end

class FlowFragmentManagerStackChangedListener
  def initialize(navigation)
    @navigation = navigation
  end

  def onBackStackChanged
    @navigation.stack_changed
  end
end