CODEWITHSUNDEEP
ioscocoa-touchios7uikituicollectionview
Nick Stamas
Nick Stamas

Reputation: 1871

Start UICollectionView at bottom

In iOS 7, given a UICollectionView, how do you start it at the bottom? Think about the iOS Messages app, where when the view becomes visible it always starts at the bottom (most recent message).

Upvotes: 13

Views: 8392

Answers (7)

J Armaggedon
J Armaggedon

Reputation: 61

added in scrollToItemAtIndexPath:atScrollPosition:animated: in viewWillLayoutSubviews so that the collectionView will be loaded instantly at the bottom

Upvotes: 0

hothead
hothead

Reputation: 131

it works perfectly for me (autolayout)

  1. Calculate ScrollView's Content Size using collectionViewFlowLayout and cellSize
  2. collectionView.contentSize = calculatedContentSize
  3. collectionView.scrollToItemAtIndexPath(whichYouWantToScrollIndexPath, atScrollPosition: ...)

Upvotes: 0

codingiran
codingiran

Reputation: 423

@awolf Your solution is good! But do not work well with autolayout.

You should call [self.view layoutIfNeeded] first! Full solution is:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    // ---- autolayout ----
    [self.view layoutIfNeeded];

    CGSize contentSize = [self.collectionView.collectionViewLayout collectionViewContentSize];
    if (contentSize.height > self.collectionView.bounds.size.height) {
        CGPoint targetContentOffset = CGPointMake(0.0f, contentSize.height - self.collectionView.bounds.size.height);
        [self.collectionView setContentOffset:targetContentOffset];
    }
}

Upvotes: 7

duan
duan

Reputation: 8875

This works for me and i think it is a modern way.

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    self.collectionView!.scrollToItemAtIndexPath(indexForTheLast, atScrollPosition: UICollectionViewScrollPosition.Bottom, animated: false)
}

Upvotes: 3

awolf
awolf

Reputation: 1972

The problem is that if you try to set the contentOffset of your collection view in viewWillAppear, the collection view hasn't rendered its items yet. Therefore self.collectionView.contentSize is still {0,0}. The solution is to ask the collection view's layout for the content size.

Additionally, you'll want to make sure that you only set the contentOffset when the contentSize is taller than the bounds of your collection view.

A full solution looks like:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    CGSize contentSize = [self.collectionView.collectionViewLayout collectionViewContentSize];
    if (contentSize.height > self.collectionView.bounds.size.height) {
        CGPoint targetContentOffset = CGPointMake(0.0f, contentSize.height - self.collectionView.bounds.size.height);
        [self.collectionView setContentOffset:targetContentOffset];
    }
}

Upvotes: 4

Schrodingrrr
Schrodingrrr

Reputation: 4271

yourCollectionView.contentOffset = CGPointMake(0, yourCollectionView.contentSize.height - yourCollectionView.bounds.size.height);

But remember to do this only when your contentSize.height > bounds.size.height.

Upvotes: 1

Flexicoder
Flexicoder

Reputation: 8511

Assuming that you know how many items are in your collection view you can use

scrollToItemAtIndexPath:atScrollPosition:animated:

Apple Docs

Upvotes: 0

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