怎么在NavigationBar加left，这些控件本身只能在固定位置上

写入代码

UIImage* backImage = [UIImage imageNamed:@"nav_order_more"];
    CGRect backframe = CGRectMake(0,0,30,8);
    UIButton* backButton= [[UIButton alloc] initWithFrame:backframe];
    [backButton setBackgroundImage:backImage forState:UIControlStateNormal];
    backButton.titleLabel.font=[UIFont systemFontOfSize:13];
    [backButton addTarget:self action:@selector(doClickBackAction) forControlEvents:UIControlEventTouchUpInside];
    
    UIBarButtonItem* setRightBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
    self.navigationItem.rightBarButtonItem = setRightBarButtonItem;

• UIImage -> UIButton -> UIBarButtonItem -> self.navigationItem(逻辑)

• UIBarButtonItem 是一个类
• 通过initWithCustomView方法，实现UIButton -> UIBarButtonItem

怎么在navigationBar加个 Center,这些控件本身只能在固定位置上

 JRSegmentControl *segment = [[JRSegmentControl alloc] initWithFrame:CGRectMake(0, 0, self.itemWidth * self.viewControllers.count, self.itemHeight) titles:self.titles];

    segment.backgroundColor = self.segmentBgColor;
    segment.indicatorViewColor = self.indicatorViewColor;

    segment.delegate = self;
    self.navigationItem.titleView = segment;

• JRSegmentControl -> self.navigationItem.titleView

• 通过赋值的方式 self.navigationItem.titleView = segment;

如何在navigationBar在任意位置加控件

UISegmentedControl * contorl = [[UISegmentedControl alloc] initWithItems:@[@"全部",@"待收货",@"待评价"]];
    contorl.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-150/2, 2, 150, 40);
    [contorl addTarget:self action:@selector(clickSegment:) forControlEvents:UIControlEventValueChanged];
    //默认选择为第一个
    contorl.selectedSegmentIndex = 0;
    [self.navigationController.navigationBar addSubview:contorl];

UISegmentedControl -> self.navigationController.navigationBar

• 通过addSubView的方式

• [self.navigationController.navigationBar addSubview:contorl];

总结：导航栏上只能加UIBarButtonItem，不能直接加控件