Ilya Laktyushin Ilya Laktyushin - 5 months ago 44
iOS Question

UIRefreshControl with UICollectionView in iOS7

In my application I use refresh control with collection view.

UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:[UIScreen mainScreen].bounds];
collectionView.alwaysBounceVertical = YES;
...
[self.view addSubview:collectionView];

UIRefreshControl *refreshControl = [UIRefreshControl new];
[collectionView addSubview:refreshControl];


iOS7 has some nasty bug that when you pull collection view down and don't release your finger when refreshing begins, vertical
contentOffset
shifts for 20-30 points down which results in ugly scroll jump.

Tables have this problem too if you use them with refresh control outside of
UITableViewController
. But for them it could be easily solved by assigning your
UIRefreshControl
instance to
UITableView
's private property called
_refreshControl
:

@interface UITableView ()
- (void)_setRefreshControl:(UIRefreshControl *)refreshControl;
@end

...

UITableView *tableView = [[UITableView alloc] initWithFrame:[UIScreen mainScreen].bounds];
[self.view addSubview:tableView];

UIRefreshControl *refreshControl = [UIRefreshControl new];
[tableView addSubview:refreshControl];
[tableView _setRefreshControl:refreshControl];


But
UICollectionView
does not have such property so there must be some way to deal with it manually.

Answer

Having the same problem and found a workaround that seems to fix it.

This seems to be happening because the UIScrollView is slowing down the tracking of the pan gesture when you pull past the edge of the scrollview. However, UIScrollView is not accounting for changes to contentInset during tracking. UIRefreshControl changes contentInset when it activates, and this change is causing the jump.

Overriding setContentInset on your UICollectionView and accounting for this case seems to help:

- (void)setContentInset:(UIEdgeInsets)contentInset {
  if (self.tracking) {
    CGFloat diff = contentInset.top - self.contentInset.top;
    CGPoint translation = [self.panGestureRecognizer translationInView:self];
    translation.y -= diff * 3.0 / 2.0;
    [self.panGestureRecognizer setTranslation:translation inView:self];
  }
  [super setContentInset:contentInset];
}

Interestingly, UITableView accounts for this by NOT slowing down tracking until you pull PAST the refresh control. However, I don't see a way that this behavior is exposed.

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