效果图

2.gif

代码实现

@interface ViewController ()<UIScrollViewDelegate>

@property (nonatomic,strong) UIScrollView* scrollView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.title = @"首页";
    
    [self.view addSubview:self.scrollView];
    self.scrollView.contentSize = CGSizeMake(0, 3*self.view.bounds.size.height);
}

//当scrollView滚动的时候调用的代理方法
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
    
    //scrollView已经有拖拽手势，直接拿到scrollView的拖拽手势
    UIPanGestureRecognizer* pan = scrollView.panGestureRecognizer;
    //获取到拖拽的速度 >0 向下拖动 <0 向上拖动
    CGFloat velocity = [pan velocityInView:scrollView].y;
    
    if (velocity<-5) {
        
        //向上拖动，隐藏导航栏
        [self.navigationController setNavigationBarHidden:true animated:true];
    }
    else if (velocity>5) {
        //向下拖动，显示导航栏
        [self.navigationController setNavigationBarHidden:false animated:true];
    }
    else if(velocity==0){
        
        //停止拖拽
    }
    
}

//view将要消失的时候，显示导航栏，这样跳转到其他界面的时候，才能看到导航栏，否则，看不到导航栏
- (void)viewWillDisappear:(BOOL)animated {

    [super viewWillDisappear:animated];
    
    [self.navigationController setNavigationBarHidden:false animated:true];
}


- (UIScrollView *)scrollView{

    if (_scrollView==nil) {
        
        _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
        _scrollView.backgroundColor = [UIColor orangeColor];
        _scrollView.delegate = self;
    }
    
    return _scrollView;
}