UINavigationItem的那点事

// 用自定义的view来替换标题
@property(nullable, nonatomic,strong) UIView    *titleView;

// 左、右标题
@property(nullable, nonatomic,strong) UIBarButtonItem *leftBarButtonItem;
@property(nullable, nonatomic,strong) UIBarButtonItem *rightBarButtonItem;

// UIBarButtonItem父类（UIBarItem）的属性，用来修改item的位置
@property(nonatomic)  UIEdgeInsets imageInsets;  // default is UIEdgeInsetsZero

// 示例
// 左右标题位置设置
UIBarButtonItem *leftItem = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:imageName] style:UIBarButtonItemStylePlain target:self action:nil];
leftItem.imageInsets = UIEdgeInsetsMake(0, 0, 12, 0); // UIEdgeInsetsMake(<#CGFloat top#>, <#CGFloat left#>, <#CGFloat bottom#>, <#CGFloat right#>)

self.navigationItem.leftBarButtonItem = leftItem;

// titleView位置，在这有个专门的方法来设置他的上下位置
- (void)setTitleVerticalPositionAdjustment:(CGFloat)adjustment forBarMetrics:(UIBarMetrics)barMetrics;
// 这里我是用[UINavigationBar appearance]调出程序所有的UINavigationController 在appdaelegate.m 里面同一添加设置(UINavigationController通用的属性都可以统一设置)
[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-12 forBarMetrics:UIBarMetricsDefault];