iPhone標準の写真アプリみたいに選択するとチェックマークが付くUIImageView

selectable_image_view.rb

class SelectableImageView < UIImageView
  include BW::KVO
  attr_accessor :is_selected

  def initWithFrame(rect)
    super
    @is_selected = false

    observe(self, :is_selected) do |old_val, new_val|
      if old_val != new_val
        if new_val
          addSubview(cover_view)
          addSubview(check_view)
        else
          cover_view.removeFromSuperview
          check_view.removeFromSuperview
        end
      end
    end
    self
  end

  def dealloc
    unobserve_all
    super
  end

  def select!
    self.is_selected = true
  end

  def deselect!
    self.is_selected = false
  end

  def toggle_selected!
    self.is_selected = !@is_selected
  end

  def selected?
    @is_selected
  end

  def cover_view
    @cover_view ||= UIView.new.tap do |v|
      v.frame = self.bounds
      v.backgroundColor = UIColor.whiteColor
      v.alpha = 0.2
    end
  end

  def check_view
    @check_view ||= UIImageView.alloc.initWithImage(UIImage.imageNamed('image_check.png')).tap do |iv|
      iv.frame = [
        [self.frame.size.width-25, self.frame.size.height-25],
        [25, 25]
      ]
      iv.opaque = false
    end
  end
end

BubbleWrapとチェックマークのPNG画像が必要。