Log:
Failed to instantiate the default view controller for UIMainStoryboardFile 'MainStoryboard' - perhaps the designated entry point is not set?
原因 ：StoryBoard 中没有一个 view controller 作为入口
在 Storyboard 中，选择一个 view conroller，将 "Is Initial View Controller" 属性勾上，作为 story board 的第一启动界面
