UIImageView drawRect

由于排版问题，需要在UIImageView上添加分割线。最开始的想法是在继承它，并在子类的drawRect:方法中用CoreGraphic API手动画上线条。 尝试过后发现完全不起作用，查了相关资料，发现UIImageView不支持重写drawRect:，文档提示如下

    Subclassing Notes
    Special Considerations

    The UIImageView class is optimized to draw its images to the display.
 UIImageView will not call the drawRect: method of a subclass. If your 
 subclass needs custom drawing code, it is recommended you use UIView as 
 the base class.

def show
  @widget = Widget(params[:id])
  respond_to do |format|
    format.html # show.html.erb
    format.json { render json: @widget }
  end
end

最后解决方式是在UIImageView添加CALayer，在CALayer把线条画出来