UINavigationItem 是 UINavigationBar 上的东西

导航栏是通过push与pop的堆栈操作来对item进行管理的，同样，每一个Item自身也有许多属性可供我们进行自定制。

Item，从英文上来理解，它可以解释为一个项目，因此，item不是一个简单的label标题，也不是一个简单的button按钮，它是导航栏中管理的一个项目的抽象。说起来有些难于理解，通过代码，我们就能很好的理解Item的意义。

 

 

以下是一些方法和属性

//NS_CLASS_AVAILABLE_IOS(2_0) @interface UINavigationItem : NSObject <NSCoding>
//
//初始化一个带有文本的UINavigationItem
  - (instancetype)initWithTitle:(NSString *)title NS_DESIGNATED_INITIALIZER;
  - (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
//
//设置和获取UINavigationItem的文本
  @property(nullable, nonatomic,copy)   NSString        *title;             // Title when topmost on the stack. default is nil
//设置一个View类型的item：
  @property(nullable, nonatomic,strong) UIView          *titleView;         // Custom view to use in lieu of a title. May be sized horizontally. Only used when item is topmost on the stack.

//这段文字会显示在item的上方：
  @property(nullable,nonatomic,copy)   NSString *prompt __TVOS_PROHIBITED;     // Explanatory text to display above the navigation bar buttons.

//一个UINavigationItem中，还可以包含许多BarButtonItem，BarButtonItem是一系列的按钮，会出现在导航栏的左侧或者右侧
//设置返回按钮
  @property(nullable,nonatomic,strong) UIBarButtonItem *backBarButtonItem __TVOS_PROHIBITED; // Bar button item to use for the back button in the child navigation item.
//
//设置在push出来新的item的时候，隐藏前面的返回按钮
  @property(nonatomic,assign) BOOL hidesBackButton __TVOS_PROHIBITED; // If YES, this navigation item will hide the back button when it's on top of the stack.
  - (void)setHidesBackButton:(BOOL)hidesBackButton animated:(BOOL)animated __TVOS_PROHIBITED;
//
///* Use these properties to set multiple items in a navigation bar.
// The older single properties (leftBarButtonItem and rightBarButtonItem) now refer to
// the first item in the respective array of items.
//
// NOTE: You'll achieve the best results if you use either the singular properties or
// the plural properties consistently and don't try to mix them.
//
// leftBarButtonItems are placed in the navigation bar left to right with the first
// item in the list at the left outside edge and left aligned.
// rightBarButtonItems are placed right to left with the first item in the list at
// the right outside edge and right aligned.
// */
//设置左右按钮组
  @property(nullable,nonatomic,copy) NSArray<UIBarButtonItem *> *leftBarButtonItems NS_AVAILABLE_IOS(5_0);
  @property(nullable,nonatomic,copy) NSArray<UIBarButtonItem *> *rightBarButtonItems NS_AVAILABLE_IOS(5_0);
  - (void)setLeftBarButtonItems:(nullable NSArray<UIBarButtonItem *> *)items animated:(BOOL)animated NS_AVAILABLE_IOS(5_0);
  - (void)setRightBarButtonItems:(nullable NSArray<UIBarButtonItem *> *)items animated:(BOOL)animated NS_AVAILABLE_IOS(5_0);
//
///* By default, the leftItemsSupplementBackButton property is NO. In this case,
// the back button is not drawn and the left item or items replace it. If you
// would like the left items to appear in addition to the back button (as opposed to instead of it)
// set leftItemsSupplementBackButton to YES.
// */
//是否隐藏返回按钮，
  @property(nonatomic) BOOL leftItemsSupplementBackButton NS_AVAILABLE_IOS(5_0) __TVOS_PROHIBITED;
//
//// Some navigation items want to display a custom left or right item when they're on top of the stack.
//// A custom left item replaces the regular back button unless you set leftItemsSupplementBackButton to YES
//设置左右按钮
  @property(nullable, nonatomic,strong) UIBarButtonItem *leftBarButtonItem;
  @property(nullable, nonatomic,strong) UIBarButtonItem *rightBarButtonItem;
  - (void)setLeftBarButtonItem:(nullable UIBarButtonItem *)item animated:(BOOL)animated;
  - (void)setRightBarButtonItem:(nullable UIBarButtonItem *)item animated:(BOOL)animated;
//
  @end