I have a collection view that scrolls horizontally and spans its parent view's full width. My cheap way to achieve paging on it is to set the cell widths to be equal to 1/3 of the collection view width, and to set that same amount of width as left and right content insets.
I disable scrolling in IB and replace with left and right swipe recognizers. My code almost works without setting contentInset, but setting the contentInset seems prevent any scrolling from happening
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
CGFloat itemWidth = self.collectionView.bounds.size.width/3.0;
NSInteger count = [self collectionView:self.collectionView numberOfItemsInSection:0];
self.collectionView.contentSize = (CGSize){ .width=itemWidth*count, .height=self.collectionView.bounds.size.height };
// uncomment this line, and the scroll code in the swipes below fails to work
//self.collectionView.contentInset = UIEdgeInsetsMake(0, itemWidth, 0, itemWidth);
self.collectionView.contentOffset = (CGPoint){ .x=self.collectionView.contentSize.width/2.0, .y=0 };
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
CGFloat width = self.view.bounds.size.width/3.0;
return (CGSize){ .width=width, .height=collectionView.bounds.size.height };
}
This code handles the swipes...
- (NSIndexPath *)centerIndexPath {
CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};
CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
return [self.collectionView indexPathForItemAtPoint:visiblePoint];
}
- (void)swipeLeft:(UISwipeGestureRecognizer *)gr {
NSIndexPath *centerIndexPath = [self centerIndexPath];
NSLog(#"at %#", centerIndexPath);
if (centerIndexPath.row < [self collectionView:self.collectionView numberOfItemsInSection:0]-1) {
[self.collectionView scrollToItemAtIndexPath:centerIndexPath atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];
}
}
- (void)swipeRight:(UISwipeGestureRecognizer *)gr {
NSIndexPath *centerIndexPath = [self centerIndexPath];
NSLog(#"at %#", centerIndexPath);
if (centerIndexPath.row > 0) {
[self.collectionView scrollToItemAtIndexPath:centerIndexPath atScrollPosition:UICollectionViewScrollPositionRight animated:YES];
}
}
All of this works, except when I set the contentInsets in the setup above. Then, even though I reach the scrollToItemAtIndexPath: code in the debugger, no scrolling occurs.
It's important to have those insets, because I want user to understand that center item is the selected item.
Can somebody explain why contentInset spoils scrolling and how to fix?
It looks like UICollectionView has its own built-in way to handle insets:
https://developer.apple.com/library/content/documentation/WindowsViews/Conceptual/CollectionViewPGforIOS/UsingtheFlowLayout/UsingtheFlowLayout.html#//apple_ref/doc/uid/TP40012334-CH3-SW1
Using Section Insets to Tweak the Margins of Your Content
Section insets are a way to adjust the space available for laying out cells. You can use insets to insert space after a section’s header view and before its footer view. You can also use insets to insert space around the sides of the content. Figure 3-5 demonstrates how insets affect some content in a vertically scrolling flow layout.
Figure 3-5 Section insets change the available space for laying out cells
I have a issue that my viewDidLayoutSubviews creates a strange offset between my table wiche is right under the view and my view
I for example uncomment this section of my code and scroll in my table this content view diapers as soon as I start to scroll
looks like this:
Offset between view and table
I really do not have a clue why this exists. The problem is not regarding the constrains I have tested it with connecting the view with the code and not.
What I do
-(void)viewDidLayoutSubviews{
[super viewDidLayoutSubviews];
[self.TableView setContentInset:UIEdgeInsetsMake(self.ContainerView.frame.size.height, 0.f, 0.f, 0.f)];
[self.TableView scrollRectToVisible:CGRectMake(0, 0, 1, 1) animated:NO];
float headerImageYOffset = 88 + self.ContainerView.bounds.size.height - self.view.bounds.size.height;
CGRect headerImageFrame = _ContainerView.frame;
headerImageFrame.origin.y = headerImageYOffset;
}
What I do when I scroll
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
CGFloat scrollOffset =-scrollView.contentOffset.y;
CGFloat yPos = scrollOffset - _obergurglContainerView.bounds.size.height;
_obergurglContainerView.frame = CGRectMake(0, yPos, _obergurglContainerView.frame.size.width, _obergurglContainerView.frame.size.height);
float Alpha = 1.0-(-yPos/_obergurglContainerView.frame.size.height);
_obergurglTitleImageView.alpha = Alpha;
NSLog(#"THE Alpha Value : %f", Alpha);
NSLog(#"The off set of the scroll view is %f",scrollOffset);
}
Thanks for help and fast answer ! :)
So reading again the question I figured out about your problem.
I think you shouldn't use viewDidLayoutSubviews.
viewDidLayoutSubviews is called all the time while you are scrolling, which is modifying the inset in your tableview all the time.
try to place
[self.TableView setContentInset:UIEdgeInsetsMake(self.ContainerView.frame.size.height, 0.f, 0.f, 0.f)];
where you create your tableview.
I have a UITableView with changing height.
I wanted in every cell selection to kind of get the 'focus' on it by moving it to the middle of the screen. The problem is to move the upper and lower cells in the table since they cannot scroll beyond the table upper and lower bounds. I'll also prefer to do this with animations..
Any suggestions?
Thanks!
I created small example of how to achieve this:
https://github.com/vkozlovskyi/CenterCellExample
You just need to calculate scroll offset of UITableView, and and animate the change:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// Get offset for cell
CGFloat centerOffset = self.tableView.frame.size.height / 2 - self.tableView.rowHeight / 2;
// Content offset
CGFloat total = indexPath.row * self.tableView.rowHeight;
[UIView animateWithDuration:0.3 animations:^{
self.tableView.contentOffset = CGPointMake(0, total - centerOffset);
}];
}
It works for all cells, upper and lower too.
You can add extra space to the content of your table view using the contentInset property. Add extra space above and below your table view will allow your cells to scroll all the way to the middle of your table view.
UITableView * tableView = self.tableView ;
CGRect bounds = self.tableView.bounds ;
CGFloat extraSpaceNeeded = 0.5 * ( bounds.size.height - tableView.rowHeight ) ;
tableView.contentInset = (UIEdgeInsets){ .top = -extraSpaceNeeded, .bottom = -extraSpaceNeeded } ;
Now you can just use
[tableView scrollToRowAtIndexPath:indexPath
atScrollPosition:UITableViewScrollPositionMiddle
animated:animated];
I want the reordering figure (three lines) to be displayed on the left side of a UITableViewCell, since the right side would be hidden by an overlaying UIView.
This code I found:
- (void) tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
for(UIView* view in cell.subviews)
{
if([[[view class] description] isEqualToString:#"UITableViewCellReorderControl"])
{
// Creates a new subview the size of the entire cell
UIView *movedReorderControl = [[UIView alloc] initWithFrame:CGRectMake(0, 0, CGRectGetMaxX(view.frame), CGRectGetMaxY(view.frame))];
// Adds the reorder control view to our new subview
[movedReorderControl addSubview:view];
// Adds our new subview to the cell
[cell addSubview:movedReorderControl];
// CGStuff to move it to the left
CGSize moveLeft = CGSizeMake(movedReorderControl.frame.size.width - view.frame.size.width, movedReorderControl.frame.size.height - view.frame.size.height);
CGAffineTransform transform = CGAffineTransformIdentity;
transform = CGAffineTransformTranslate(transform, -moveLeft.width, -moveLeft.height);
// Performs the transform
[movedReorderControl setTransform:transform];
}
}
}
Works just fine when the table gets loaded for the first time.
However, when cells get "redrawn" (like when scrolling fore and back) the reordering symbol just disappears.
What is going wrong?
You keep moving the reorder control relative to its current position
CGSize moveLeft = CGSizeMake(movedReorderControl.frame.size.width - view.frame.size.width, movedReorderControl.frame.size.height - view.frame.size.height);
so it seems like its moving it off screen. Try storing the initial frame and then using that to shift your subview:
CGSize moveLeft = CGSizeMake(initialFrame.width - view.frame.size.width, initialFrame.width.height - view.frame.size.height);
The code should go in the drawRect: method of the UITableView cell so that it's called whenever the cell is updated. It should be the cell's responsibility to draw itself, not the view.
I'm trying to handle interface orientation changes in a UICollectionViewController. What I'm trying to achieve is, that I want to have the same contentOffset after an interface rotation. Meaning, that it should be changed corresponding to the ratio of the bounds change.
Starting in portrait with a content offset of {bounds.size.width * 2, 0} …
… should result to the content offset in landscape also with {bounds.size.width * 2, 0} (and vice versa).
Calculating the new offset is not the problem, but don't know, where (or when) to set it, to get a smooth animation. What I'm doing so fare is invalidating the layout in willRotateToInterfaceOrientation:duration: and resetting the content offset in didRotateFromInterfaceOrientation::
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation
duration:(NSTimeInterval)duration;
{
self.scrollPositionBeforeRotation = CGPointMake(self.collectionView.contentOffset.x / self.collectionView.contentSize.width,
self.collectionView.contentOffset.y / self.collectionView.contentSize.height);
[self.collectionView.collectionViewLayout invalidateLayout];
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation;
{
CGPoint newContentOffset = CGPointMake(self.scrollPositionBeforeRotation.x * self.collectionView.contentSize.width,
self.scrollPositionBeforeRotation.y * self.collectionView.contentSize.height);
[self.collectionView newContentOffset animated:YES];
}
This changes the content offset after the rotation.
How can I set it during the rotation? I tried to set the new content offset in willAnimateRotationToInterfaceOrientation:duration: but this results into a very strange behavior.
An example can be found in my Project on GitHub.
You can either do this in the view controller:
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
guard let collectionView = collectionView else { return }
let offset = collectionView.contentOffset
let width = collectionView.bounds.size.width
let index = round(offset.x / width)
let newOffset = CGPoint(x: index * size.width, y: offset.y)
coordinator.animate(alongsideTransition: { (context) in
collectionView.reloadData()
collectionView.setContentOffset(newOffset, animated: false)
}, completion: nil)
}
Or in the layout itself: https://stackoverflow.com/a/54868999/308315
Solution 1, "just snap"
If what you need is only to ensure that the contentOffset ends in a right position, you can create a subclass of UICollectionViewLayout and implement targetContentOffsetForProposedContentOffset: method. For example you could do something like this to calculate the page:
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
{
NSInteger page = ceil(proposedContentOffset.x / [self.collectionView frame].size.width);
return CGPointMake(page * [self.collectionView frame].size.width, 0);
}
But the problem that you'll face is that the animation for that transition is extremely weird. What I'm doing on my case (which is almost the same as yours) is:
Solution 2, "smooth animation"
1) First I set the cell size, which can be managed by collectionView:layout:sizeForItemAtIndexPath: delegate method as follows:
- (CGSize)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)collectionViewLayout
sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
return [self.view bounds].size;
}
Note that [self.view bounds] will change according to the device rotation.
2) When the device is about to rotate, I'm adding an imageView on top of the collection view with all resizing masks. This view will actually hide the collectionView weirdness (because it is on top of it) and since the willRotatoToInterfaceOrientation: method is called inside an animation block it will rotate accordingly. I'm also keeping the next contentOffset according to the shown indexPath so I can fix the contentOffset once the rotation is done:
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation
duration:(NSTimeInterval)duration
{
// Gets the first (and only) visible cell.
NSIndexPath *indexPath = [[self.collectionView indexPathsForVisibleItems] firstObject];
KSPhotoViewCell *cell = (id)[self.collectionView cellForItemAtIndexPath:indexPath];
// Creates a temporary imageView that will occupy the full screen and rotate.
UIImageView *imageView = [[UIImageView alloc] initWithImage:[[cell imageView] image]];
[imageView setFrame:[self.view bounds]];
[imageView setTag:kTemporaryImageTag];
[imageView setBackgroundColor:[UIColor blackColor]];
[imageView setContentMode:[[cell imageView] contentMode]];
[imageView setAutoresizingMask:0xff];
[self.view insertSubview:imageView aboveSubview:self.collectionView];
// Invalidate layout and calculate (next) contentOffset.
contentOffsetAfterRotation = CGPointMake(indexPath.item * [self.view bounds].size.height, 0);
[[self.collectionView collectionViewLayout] invalidateLayout];
}
Note that my subclass of UICollectionViewCell has a public imageView property.
3) Finally, the last step is to "snap" the content offset to a valid page and remove the temporary imageview.
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation
{
[self.collectionView setContentOffset:contentOffsetAfterRotation];
[[self.view viewWithTag:kTemporaryImageTag] removeFromSuperview];
}
The "just snap" answer above didn't work for me as it frequently didn't end on the item that was in view before the rotate. So I derived a flow layout that uses a focus item (if set) for calculating the content offset. I set the item in willAnimateRotationToInterfaceOrientation and clear it in didRotateFromInterfaceOrientation. The inset adjustment seems to be need on IOS7 because the Collection view can layout under the top bar.
#interface HintedFlowLayout : UICollectionViewFlowLayout
#property (strong)NSIndexPath* pathForFocusItem;
#end
#implementation HintedFlowLayout
-(CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
{
if (self.pathForFocusItem) {
UICollectionViewLayoutAttributes* layoutAttrs = [self layoutAttributesForItemAtIndexPath:self.pathForFocusItem];
return CGPointMake(layoutAttrs.frame.origin.x - self.collectionView.contentInset.left, layoutAttrs.frame.origin.y-self.collectionView.contentInset.top);
}else{
return [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
}
}
#end
Swift 4.2 subclass:
class RotatableCollectionViewFlowLayout: UICollectionViewFlowLayout {
private var focusedIndexPath: IndexPath?
override func prepare(forAnimatedBoundsChange oldBounds: CGRect) {
super.prepare(forAnimatedBoundsChange: oldBounds)
focusedIndexPath = collectionView?.indexPathsForVisibleItems.first
}
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
guard let indexPath = focusedIndexPath
, let attributes = layoutAttributesForItem(at: indexPath)
, let collectionView = collectionView else {
return super.targetContentOffset(forProposedContentOffset: proposedContentOffset)
}
return CGPoint(x: attributes.frame.origin.x - collectionView.contentInset.left,
y: attributes.frame.origin.y - collectionView.contentInset.top)
}
override func finalizeAnimatedBoundsChange() {
super.finalizeAnimatedBoundsChange()
focusedIndexPath = nil
}
}
For those using iOS 8+, willRotateToInterfaceOrientation and didRotateFromInterfaceOrientation are deprecated.
You should use the following now:
/*
This method is called when the view controller's view's size is changed by its parent (i.e. for the root view controller when its window rotates or is resized).
If you override this method, you should either call super to propagate the change to children or manually forward the change to children.
*/
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id <UIViewControllerTransitionCoordinator>)coordinator
{
[super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
[coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {
// Update scroll position during rotation animation
self.collectionView.contentOffset = (CGPoint){contentOffsetX, contentOffsetY};
} completion:^(id<UIViewControllerTransitionCoordinatorContext> context) {
// Whatever you want to do when the rotation animation is done
}];
}
Swift 3:
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
coordinator.animate(alongsideTransition: { (context:UIViewControllerTransitionCoordinatorContext) in
// Update scroll position during rotation animation
}) { (context:UIViewControllerTransitionCoordinatorContext) in
// Whatever you want to do when the rotation animation is done
}
}
I think the correct solution is to override targetContentOffsetForProposedContentOffset: method in a subclassed UICollectionViewFlowLayout
From the docs:
During layout updates, or when transitioning between layouts, the
collection view calls this method to give you the opportunity to
change the proposed content offset to use at the end of the animation.
You might override this method if the animations or transition might
cause items to be positioned in a way that is not optimal for your
design.
To piggy back off troppoli's solution you can set the offset in your custom class without having to worry about remembering to implement the code in your view controller. prepareForAnimatedBoundsChange should get called when you rotate the device then finalizeAnimatedBoundsChange after its done rotating.
#interface OrientationFlowLayout ()
#property (strong)NSIndexPath* pathForFocusItem;
#end
#implementation OrientationFlowLayout
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset {
if (self.pathForFocusItem) {
UICollectionViewLayoutAttributes* layoutAttrs = [self layoutAttributesForItemAtIndexPath:
self.pathForFocusItem];
return CGPointMake(layoutAttrs.frame.origin.x - self.collectionView.contentInset.left,
layoutAttrs.frame.origin.y - self.collectionView.contentInset.top);
}
else {
return [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
}
}
- (void)prepareForAnimatedBoundsChange:(CGRect)oldBounds {
[super prepareForAnimatedBoundsChange:oldBounds];
self.pathForFocusItem = [[self.collectionView indexPathsForVisibleItems] firstObject];
}
- (void)finalizeAnimatedBoundsChange {
[super finalizeAnimatedBoundsChange];
self.pathForFocusItem = nil;
}
#end
This problem bothered me for a bit as well. The highest voted answered seemed a bit too hacky for me so I just dumbed it down a bit and just change the alpha of the collection view respectively before and after rotation. I also don't animate the content offset update.
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
{
self.collectionView.alpha = 0;
[self.collectionView.collectionViewLayout invalidateLayout];
self.scrollPositionBeforeRotation = CGPointMake(self.collectionView.contentOffset.x / self.collectionView.contentSize.width,
self.collectionView.contentOffset.y / self.collectionView.contentSize.height);
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation;
{
CGPoint newContentOffset = CGPointMake(self.scrollPositionBeforeRotation.x * self.collectionView.contentSize.width,
self.scrollPositionBeforeRotation.y * self.collectionView.contentSize.height);
[self.collectionView setContentOffset:newContentOffset animated:NO];
self.collectionView.alpha = 1;
}
Fairly smooth and less hacky.
I use a variant of fz. answer (iOS 7 & 8) :
Before rotation :
Store the current visible index path
Create a snapshot of the collectionView
Put an UIImageView with it on top of the collection view
After rotation :
Scroll to the stored index
Remove the image view.
#property (nonatomic) NSIndexPath *indexPath;
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation
duration:(NSTimeInterval)duration {
self.indexPathAfterRotation = [[self.collectionView indexPathsForVisibleItems] firstObject];
// Creates a temporary imageView that will occupy the full screen and rotate.
UIGraphicsBeginImageContextWithOptions(self.collectionView.bounds.size, YES, 0);
[self.collectionView drawViewHierarchyInRect:self.collectionView.bounds afterScreenUpdates:YES];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
[imageView setFrame:[self.collectionView bounds]];
[imageView setTag:kTemporaryImageTag];
[imageView setBackgroundColor:[UIColor blackColor]];
[imageView setContentMode:UIViewContentModeCenter];
[imageView setAutoresizingMask:0xff];
[self.view insertSubview:imageView aboveSubview:self.collectionView];
[[self.collectionView collectionViewLayout] invalidateLayout];
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation {
[self.collectionView scrollToItemAtIndexPath:self.indexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];
[[self.view viewWithTag:kTemporaryImageTag] removeFromSuperview];
}
After rotate interface orientation the UICollectionViewCell usually move to another position, because we won't update contentSize and contentOffset.
So the visible UICollectionViewCell always not locate at expected position.
The visible UICollectionView which we expected image as follow
Orientation which we expected
UICollectionView must delegate the function [collectionView sizeForItemAtIndexPath] of『UICollectionViewDelegateFlowLayout』.
And you should calculate the item Size in this function.
The custom UICollectionViewFlowLayout must override the functions as follow.
-(void)prepareLayout
． Set itemSize, scrollDirection and others.
-(CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
． Calculate page number or calculate visible content offset.
-(CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
． Return visual content offset.
-(CGSize)collectionViewContentSize
． Return the total content size of collectionView.
Your viewController must override 『willRotateToInterfaceOrientation』and in this function
you should call the function [XXXCollectionVew.collectionViewLayout invalidateLayout];
But 『willRotateToInterfaceOrientation』 is deprecated in iOS 9, or you could call the function [XXXCollectionVew.collectionViewLayout invalidateLayout] in difference way.
There's an example as follow :
https://github.com/bcbod2002/CollectionViewRotationTest
in Swift 3.
you should track which cell item(Page) is being presented before rotate by indexPath.item, the x coordinate or something else.
Then, in your UICollectionView:
override func collectionView(_ collectionView: UICollectionView, targetContentOffsetForProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
let page:CGFloat = pageNumber // your tracked page number eg. 1.0
return CGPoint(x: page * collectionView.frame.size.width, y: -(topInset))
//the 'y' value would be '0' if you don't have any top EdgeInset
}
In my case I invalidate the layout in viewDidLayoutSubviews() so the collectionView.frame.size.width is the width of the collectionVC's view that has been rotated.
This work like a charm:
-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
return self.view.bounds.size;
}
-(void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
int currentPage = collectionMedia.contentOffset.x / collectionMedia.bounds.size.width;
float width = collectionMedia.bounds.size.height;
[UIView animateWithDuration:duration animations:^{
[self.collectionMedia setContentOffset:CGPointMake(width * currentPage, 0.0) animated:NO];
[[self.collectionMedia collectionViewLayout] invalidateLayout];
}];
}
If found that using targetContentOffsetForProposedContentOffset does not work in all scenarios and the problem with using didRotateFromInterfaceOrientation is that it gives visual artifacts. My perfectly working code is as follows:
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
{
[super willRotateToInterfaceOrientation:toInterfaceOrientation duration:duration];
_indexPathOfFirstCell = [self indexPathsForVisibleItems].firstObject;
}
- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
[super willAnimateRotationToInterfaceOrientation:toInterfaceOrientation duration:duration];
if (_indexPathOfFirstCell) {
[UIView performWithoutAnimation:^{
[self scrollToItemAtIndexPath:self->_indexPathOfFirstCell atScrollPosition:UICollectionViewScrollPositionTop animated:NO];
}];
_indexPathOfFirstCell = nil;
}
}
The key is to use the willRotateToInterfaceOrientation method to determine the part in the view that you want to scroll to and willAnimationRotationToInterfaceOrientation to recalculate it when the view has changed its size (the bounds have already changed when this method is called by the framework) and to actually scroll to the new position without animation. In my code I used the index path for the first visual cell to do that, but a percentage of contentOffset.y/contentSize.height would also do the job in slightly different way.
What does the job for me is this:
Set the size of your my cells from your my UICollectionViewDelegateFlowLayout method
func collectionView(collectionView: UICollectionView!, layout collectionViewLayout: UICollectionViewLayout!, sizeForItemAtIndexPath indexPath: NSIndexPath!) -> CGSize
{
return collectionView.bounds.size
}
After that I implement willRotateToInterfaceOrientationToInterfaceOrientation:duration: like this
override func willRotateToInterfaceOrientation(toInterfaceOrientation: UIInterfaceOrientation, duration: NSTimeInterval)
{
let currentPage = Int(collectionView.contentOffset.x / collectionView.bounds.size.width)
var width = collectionView.bounds.size.height
UIView.animateWithDuration(duration) {
self.collectionView.setContentOffset(CGPointMake(width * CGFloat(currentPage), 0.0), animated: false)
self.collectionView.collectionViewLayout.invalidateLayout()
}
}
The above code is in Swift but you get the point and it's easy to "translate"
You might want to hide the collectionView during it's (incorrect) animation and show a placeholder view of the cell that rotates correctly instead.
For a simple photo gallery I found a way to do it that looks quite good. See my answer here:
How to rotate a UICollectionView similar to the photos app and keep the current view centered?
My way is to use a UICollectionViewFlowlayout object.
Set the ojbect line spacing if it scrolls horizontally.
[flowLayout setMinimumLineSpacing:26.0f];
Set its interitem spacing if it scrolls vertically.
[flowLayout setMinimumInteritemSpacing:0.0f];
Notice it behaves different when you rotate the screen. In my case, I have it scrolls horizontally so minimumlinespacing is 26.0f. Then it seems horrible when it rotates to landscape direction. I have to check rotation and set minimumlinespacing for that direction 0.0f to make it right.
That's it! Simple.
I had the issue with my project,i used two different layout for the UICollectionView.
mCustomCell *cell = [cv dequeueReusableCellWithReuseIdentifier:#"LandScapeCell" forIndexPath:indexPath];
theCustomCell *cell = [cv dequeueReusableCellWithReuseIdentifier:#"PortraitCell" forIndexPath:indexPath];
Then Check it for each orientation and use your configuration for each orientation.
-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
CGSize pnt = CGSizeMake(70, 70);
return pnt; }
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
// UIEdgeInsetsMake(<#CGFloat top#>, <#CGFloat left#>, <#CGFloat bottom#>, <#CGFloat right#>)
return UIEdgeInsetsMake(3, 0, 3, 0); }
This way you can adjust the content offset and the size of your cell.
Use <CollectionViewDelegateFlowLayout> and in the method didRotateFromInterfaceOrientation: reload data of the CollectionView.
Implement collectionView:layout:sizeForItemAtIndexPath: method of <CollectionViewDelegateFlowLayout> and in the method verify the Interface orientation and apply your custom size of each cell.
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];
if (UIInterfaceOrientationIsPortrait(orientation)) {
return CGSizeMake(CGFloat width, CGFloat height);
} else {
return CGSizeMake(CGFloat width, CGFloat height);
}
}
I have a similar case in which i use this
- (void)setFrame:(CGRect)frame
{
CGFloat currentWidth = [self frame].size.width;
CGFloat offsetModifier = [[self collectionView] contentOffset].x / currentWidth;
[super setFrame:frame];
CGFloat newWidth = [self frame].size.width;
[[self collectionView] setContentOffset:CGPointMake(offsetModifier * newWidth, 0.0f) animated:NO];
}
This is a view that contains a collectionView.
In the superview I also do this
- (void)setFrame:(CGRect)frame
{
UICollectionViewFlowLayout *collectionViewFlowLayout = (UICollectionViewFlowLayout *)[_collectionView collectionViewLayout];
[collectionViewFlowLayout setItemSize:frame.size];
[super setFrame:frame];
}
This is to adjust the cell sizes to be full screen (full view to be exact ;) ). If you do not do this here a lot of error messages may appear about that the cell size is bigger than the collectionview and that the behaviour for this is not defined and bla bla bla.....
These to methods can off course be merged into one subclass of the collectionview or in the view containing the collectionview but for my current project was this the logical way to go.
The "just snap" answer is the right approach and doesn't require extra smoothing with snapshot overlays IMO. However there's an issue which explains why some people see that the correct page isn't scrolled to in some cases. When calculating the page, you'd want to use the height and not the width. Why? Because the view geometry has already rotated by the time targetContentOffsetForProposedContentOffset is called, and so what was the width is now the height. Also rounding is more sensible than ceiling. So:
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
{
NSInteger page = round(proposedContentOffset.x / self.collectionView.bounds.size.height);
return CGPointMake(page * self.collectionView.bounds.size.width, 0);
}
I solved this problem with Following Steps:
Calculate currently scrolled NSIndexPath
Disable Scrolling and Pagination in UICollectionView
Apply new Flow Layout to UICollectionView
Enable Scrolling and Pagination in UICollectionView
Scroll UICollectionView to current NSIndexPath
Here is the Code Template demonstrating the Above Steps:
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation
duration:(NSTimeInterval)duration;
{
//Calculating Current IndexPath
CGRect visibleRect = (CGRect){.origin = self.yourCollectionView.contentOffset, .size = self.yourCollectionView.bounds.size};
CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
self.currentIndexPath = [self.yourCollectionView indexPathForItemAtPoint:visiblePoint];
//Disable Scrolling and Pagination
[self disableScrolling];
//Applying New Flow Layout
[self setupNewFlowLayout];
//Enable Scrolling and Pagination
[self enableScrolling];
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation;
{
//You can also call this at the End of `willRotate..` method.
//Scrolling UICollectionView to current Index Path
[self.yourCollectionView scrollToItemAtIndexPath:self.currentIndexPath atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:NO];
}
- (void) disableScrolling
{
self.yourCollectionView.scrollEnabled = false;
self.yourCollectionView.pagingEnabled = false;
}
- (void) enableScrolling
{
self.yourCollectionView.scrollEnabled = true;
self.yourCollectionView.pagingEnabled = true;
}
- (void) setupNewFlowLayout
{
UICollectionViewFlowLayout* flowLayout = [[UICollectionViewFlowLayout alloc] init];
flowLayout.sectionInset = UIEdgeInsetsMake(0, 0, 0, 0);
flowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
flowLayout.minimumInteritemSpacing = 0;
flowLayout.minimumLineSpacing = 0;
[flowLayout setItemSize:CGSizeMake(EXPECTED_WIDTH, EXPECTED_HEIGHT)];
[self.yourCollectionView setCollectionViewLayout:flowLayout animated:YES];
[self.yourCollectionView.collectionViewLayout invalidateLayout];
}
I hope this helps.
I had got some troubles with animateAlongsideTransition block in animateAlongsideTransition (see the code below).
Pay attention, that it is called during (but not before) the animation
My task was update the table view scroll position using scrolling to the top visible row (I’ve faced with the problem on iPad when table view cells shifted up when the device rotation, therefore I was founding the solution for that problem). But may be it would be useful for contentOffset too.
I tried to solve the problem by the following way:
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
[super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
__weak TVChannelsListTableViewController *weakSelf = self;
[coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> _Nonnull context) {
weakSelf.topVisibleRowIndexPath = [[weakSelf.tableView indexPathsForVisibleRows] firstObject];
} completion:^(id<UIViewControllerTransitionCoordinatorContext> _Nonnull context) {
[weakSelf.tableView scrollToRowAtIndexPath:weakSelf.topVisibleRowIndexPath atScrollPosition:UITableViewScrollPositionTop animated:NO];
}];
}
But it didn’t work. For instance, index path of the top cel was (0, 20). But when the device rotation animateAlongsideTransition block was called and [[weakSelf.tableView indexPathsForVisibleRows] firstObject] returned index path (0, 27).
I thought the problem was in retrieving index paths to weakSelf. Therefore to solve the problem I’ve moved self.topVisibleRowIndexPath before [coordinator animateAlongsideTransition: completion] method calling:
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
[super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
__weak TVChannelsListTableViewController *weakSelf = self;
self.topVisibleRowIndexPath = [[weakSelf.tableView indexPathsForVisibleRows] firstObject];
[coordinator animateAlongsideTransition:nil completion:^(id<UIViewControllerTransitionCoordinatorContext> _Nonnull context) {
[weakSelf.tableView scrollToRowAtIndexPath:weakSelf.topVisibleRowIndexPath atScrollPosition:UITableViewScrollPositionTop animated:NO];
}];
}
And the other interesting thing that I’ve discovered is that the deprecated methods willRotateToInterfaceOrientation and willRotateToInterfaceOrientation are still successful called in iOS later 8.0 when method viewWillTransitionToSize is not redefined.
So the other way to solve the problem in my case was to use deprecated method instead of new one. I think it would be not right solution, but it is possible to try if other ways don’t work :)
You might want to try this untested code:
- (void) willRotateToInterfaceOrientation: (UIInterfaceOrientation) toInterfaceOrientation
duration: (NSTimeInterval) duration
{
[UIView animateWithDuration: duration
animation: ^(void)
{
CGPoint newContentOffset = CGPointMake(self.scrollPositionBeforeRotation.x *
self.collectionView.contentSize.height,
self.scrollPositionBeforeRotation.y *
self.collectionView.contentSize.width);
[self.collectionView setContentOffset: newContentOffset
animated: YES];
}];
}