The value of the current_card method is what you want to render, and to do that, you need a view class.
current _ card方法的值就是要呈现的值，为了呈现这个值，需要一个视图类。
You may have noticed that when you selected a method in the Outline view and the Hierarchy view, the class of the selected object was not always the same.
您可能已经注意到，当您在Outline视图和Hierarchy视图中选择了一个方法时，所选对象的类并非总是相同的。
The primary method of this class is the action, which handles displaying appropriate information in the view based on the action performed by the user.
此类的主要方法为action，它基于用户执行的操作处理视图中应显示的相应信息。
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