Add a floating bar to a scroll view like in the Facebook iOS app's timeline

Question

I\'ve been playing around with adding different interactions to a test project of mine, and I\'m having trouble adding something like Facebook\'s post status bar, the one that s

Answer 1

Here's some sample code you can use to get started, just add it to your view controller. It uses a generic UIView for the floating bar and a generic UIScrollView for the scroll view but you can change that to whatever you want.

@interface BNLFDetailViewController () <UIScrollViewDelegate> {
    UIScrollView *_scrollView;
    UIView *_floatingBarView;
    CGFloat _lastOffset;
}
@end

And in the @implementation add:

- (void)viewDidLoad {
    [super viewDidLoad];

    _scrollView = [[UIScrollView alloc] initWithFrame:self.view.bounds];
    _scrollView.delegate = self;
    _scrollView.contentSize = CGSizeMake(self.view.bounds.size.width, self.view.bounds.size.height * 2);
    [self.view addSubview:_scrollView];

    CGRect f = self.view.bounds;
    f.size.height = kFloatingBarHeight;
    _floatingBarView = [[UIView alloc] initWithFrame:f];
    _floatingBarView.backgroundColor = [UIColor blackColor];
    [self.view addSubview:_floatingBarView];
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView == _scrollView) {
        CGFloat offsetChange = _lastOffset - scrollView.contentOffset.y;
        CGRect f = _floatingBarView.frame;
        f.origin.y += offsetChange;
        if (f.origin.y < -kFloatingBarHeight) f.origin.y = -kFloatingBarHeight;
        if (f.origin.y > 0) f.origin.y = 0;
        if (scrollView.contentOffset.y <= 0) f.origin.y = 0; //Deal with "bouncing" at the top
        if (scrollView.contentOffset.y + scrollView.bounds.size.height >= scrollView.contentSize.height) f.origin.y = -kFloatingBarHeight; //Deal with "bouncing" at the bottom
        _floatingBarView.frame = f;

        _lastOffset = scrollView.contentOffset.y;
    }
}

You should be doing it as a UIView, not a UIViewController. The general rule in iOS development is that view controllers take up the entire screen and views are used for "subviews" that take up part of the screen (though this is less the case for iPad). Either way, a UIViewController has it's own lifecycle (willAppear, didAppear, etc.) which is not needed/wanted for the floating bar so it should definitely be a UIView.