导航栏渐变效果

-(void)viewWillAppear:(BOOL)animated
{    [super viewWillAppear:animated];
      [UIApplication sharedApplication].statusBarStyle = UIStatusBarStyleDefault;
}

- (void)viewDidLoad {
    [super viewDidLoad];
   
    [self.view addSubview:self.YHtableview];
    
    if (_offsetY > 0 && _offsetY < 135) {
        CGFloat alpha = _offsetY/135.0;
        [self.navigationController setNavigationBarHidden:NO animated:NO];
        [[[self.navigationController.navigationBar subviews] objectAtIndex:0] setAlpha:alpha];
    } else if (_offsetY >= 135) {
        [self.navigationController setNavigationBarHidden:NO animated:NO];
        [[[self.navigationController.navigationBar subviews] objectAtIndex:0] setAlpha:1];
    } else {
        [self.navigationController setNavigationBarHidden:YES animated:NO];
    }
}

-(void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [[[self.navigationController.navigationBar subviews] objectAtIndex:0] setAlpha:1];
    [UIApplication sharedApplication].statusBarStyle = UIStatusBarStyleLightContent;
}

#pragma mark-**********懒加载***********
-(UITableView *)YHtableview
{
    if (!_YHtableview) {
        _YHtableview = [[UITableView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height) style:UITableViewStylePlain];
       _YHtableview.delegate = self;
       _YHtableview.dataSource = self;
        [_YHtableview registerClass:[UITableViewCell class] forCellReuseIdentifier:@"cell"];
        if (@available(iOS 11.0, *)) {
            _YHtableview.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
        } else {
            self.automaticallyAdjustsScrollViewInsets = NO;
        }
        UIView *TopView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, 200)];
        TopView.backgroundColor = [[UIColor redColor]colorWithAlphaComponent:0.5];
        _YHtableview.tableHeaderView = TopView;
    }
    return _YHtableview;
}

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return 1;
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];
    
    return cell;

}
-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    NSLog(@"+++++%f++++++",scrollView.contentOffset.y);
    _offsetY = scrollView.contentOffset.y;
    if (_offsetY > 0 && _offsetY < 135) {
        CGFloat alpha = _offsetY/135.0;
        [self.navigationController setNavigationBarHidden:NO animated:NO];
        [[[self.navigationController.navigationBar subviews] objectAtIndex:0] setAlpha:alpha];
    }
    if (_offsetY >= 135) {
        [self.navigationController setNavigationBarHidden:NO animated:NO];
        [[[self.navigationController.navigationBar subviews] objectAtIndex:0] setAlpha:1];
    }
    if (_offsetY <= 0) {
        [self.navigationController setNavigationBarHidden:YES animated:NO];
    }}

Simulator Screen Shot - iPhone 7 - 2018-12-06 at 14.14.42.png