cocoa touch——UINavigationBar——UINavigationItem配置

UINavigationBar

// Pushing a navigation item displays the item's title in the center of the navigation bar.// The previous top navigation item (if it exists) is displayed as a "back" button on the left.- (void)pushNavigationItem:(UINavigationItem *)item animated:(BOOL)animated;- (nullable UINavigationItem *)popNavigationItemAnimated:(BOOL)animated; // Returns the item that was popped.@property(nullable, nonatomic,readonly,strong) UINavigationItem *topItem;@property(nullable, nonatomic,readonly,strong) UINavigationItem *backItem;@property(nullable,nonatomic,copy) NSArray<UINavigationItem *> *items;- (void)setItems:(nullable NSArray<UINavigationItem *> *)items animated:(BOOL)animated; // If animated is YES, then simulate a push or pop depending on whether the new top item was previously in the stack.

注意：

• backItem是stack中topItem下的item，即second topmost item
• topItem的leftBarButtonItem如果为nil，则显示back button，用backItem的title作为back button的title，如果backItem的title为nil，则back button的title显示"Back"
• 属性items和setItems的items，array的front-to-back顺序对应stack的bottom-to-top顺序
• setItems动画显示时取决于items中的最后一项，如果最后一项不存在当前stack中，显示push动画，如果存在当前stack中且不存在于topmost中，显示pop动画，如果刚好是topmost，则无动画