NgSwitchDefault
创建一个当没有任何 NgSwitchCase 表达式能匹配 NgSwitch 表达时要渲染的视图。该语句应该是 NgSwitch 的最后一种情况。
Creates a view that is rendered when no NgSwitchCase expressions match the NgSwitch expression. This statement should be the final case in an NgSwitch.
