How would I go about disabling a UIButton if the UIScrollView has scrolled more than a certain amount?
this is what I've been trying. Perhaps it's the wrong scrollViewDidScroll: delegate method.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if (_scrollView.contentOffset.y >= 100) {
mapLaunchButton.enabled = NO;
}
}
thanks for any help
Simple! You'll need to create a variable to store the starting position of the scroll view though. It should be a CGPoint. Set it to the scroll view's content offset in scrollViewWillBeginDragging: (where the scroll view starts moving) and then do comparison in scrollViewDidScroll similarly to how you were doing it before.
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
startingPoint = scrollView.contentOffset;
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
if (scrollView.contentOffset.y >= startingPoint.y + 100.0f) {
mapLaunchButton.enabled = NO;
}
}
Keep in mind you may need to modify the values I've provided slightly depending on the starting position of the scroll view, and the direction in which you'd like to monitor the changes.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if (_scrollView.contentOffset.y >= 100) {
mapLaunchButton.enabled = NO;
}
else {
mapLaunchButton.enabled = YES;
}
}
The code is OK, but you have to add the delegate for the scrollView
- (void)viewDidLoad {
[super viewDidLoad];
// do whatever
...
// Add the delegate for the scrollview
[_scrollView setDelegate:self];
}
According to Apple's documentation (and touted at WWDC 2012), it is possible to set the layout on UICollectionView dynamically and even animate the changes:
You normally specify a layout object when creating a collection view but you can also change the layout of a collection view dynamically. The layout object is stored in the collectionViewLayout property. Setting this property directly updates the layout immediately, without animating the changes. If you want to animate the changes, you must call the setCollectionViewLayout:animated: method instead.
However, in practice, I've found that UICollectionView makes inexplicable and even invalid changes to the contentOffset, causing cells to move incorrectly, making the feature virtually unusable. To illustrate the problem, I put together the following sample code that can be attached to a default collection view controller dropped into a storyboard:
#import <UIKit/UIKit.h>
#interface MyCollectionViewController : UICollectionViewController
#end
#implementation MyCollectionViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"CELL"];
self.collectionView.collectionViewLayout = [[UICollectionViewFlowLayout alloc] init];
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
return 1;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:#"CELL" forIndexPath:indexPath];
cell.backgroundColor = [UIColor whiteColor];
return cell;
}
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"contentOffset=(%f, %f)", self.collectionView.contentOffset.x, self.collectionView.contentOffset.y);
[self.collectionView setCollectionViewLayout:[[UICollectionViewFlowLayout alloc] init] animated:YES];
NSLog(#"contentOffset=(%f, %f)", self.collectionView.contentOffset.x, self.collectionView.contentOffset.y);
}
#end
The controller sets a default UICollectionViewFlowLayout in viewDidLoad and displays a single cell on-screen. When the cells is selected, the controller creates another default UICollectionViewFlowLayout and sets it on the collection view with the animated:YES flag. The expected behavior is that the cell does not move. The actual behavior, however, is that the cell scroll off-screen, at which point it is not even possible to scroll the cell back on-screen.
Looking at the console log reveals that the contentOffset has inexplicably changed (in my project, from (0, 0) to (0, 205)). I posted a solution for the solution for the non-animated case (i.e. animated:NO), but since I need animation, I'm very interested to know if anyone has a solution or workaround for the animated case.
As a side-note, I've tested custom layouts and get the same behavior.
UICollectionViewLayout contains the overridable method targetContentOffsetForProposedContentOffset: which allows you to provide the proper content offset during a change of layout, and this will animate correctly. This is available in iOS 7.0 and above
I have been pulling my hair out over this for days and have found a solution for my situation that may help.
In my case I have a collapsing photo layout like in the photos app on the ipad. It shows albums with the photos on top of each other and when you tap an album it expands the photos. So what I have is two separate UICollectionViewLayouts and am toggling between them with [self.collectionView setCollectionViewLayout:myLayout animated:YES] I was having your exact problem with the cells jumping before animation and realized it was the contentOffset. I tried everything with the contentOffset but it still jumped during animation. tyler's solution above worked but it was still messing with the animation.
Then I noticed that it happens only when there were a few albums on the screen, not enough to fill the screen. My layout overrides -(CGSize)collectionViewContentSize as recommended. When there are only a few albums the collection view content size is less than the views content size. That's causing the jump when I toggle between the collection layouts.
So I set a property on my layouts called minHeight and set it to the collection views parent's height. Then I check the height before I return in -(CGSize)collectionViewContentSize I ensure the height is >= the minimum height.
Not a true solution but it's working fine now. I would try setting the contentSize of your collection view to be at least the length of it's containing view.
edit:
Manicaesar added an easy workaround if you inherit from UICollectionViewFlowLayout:
-(CGSize)collectionViewContentSize { //Workaround
CGSize superSize = [super collectionViewContentSize];
CGRect frame = self.collectionView.frame;
return CGSizeMake(fmaxf(superSize.width, CGRectGetWidth(frame)), fmaxf(superSize.height, CGRectGetHeight(frame)));
}
2019 actual solution
Say you have a number of layouts for your "Cars" view.
Let's say you have three.
CarsLayout1: UICollectionViewLayout { ...
CarsLayout2: UICollectionViewLayout { ...
CarsLayout3: UICollectionViewLayout { ...
It will jump when you animate between layouts.
It's just an undeniable mistake by Apple. It jumps when you animate, without question.
The fix is this:
You must have a global float, and, the following base class:
var avoidAppleMessupCarsLayouts: CGPoint? = nil
class FixerForCarsLayouts: UICollectionViewLayout {
override func prepareForTransition(from oldLayout: UICollectionViewLayout) {
avoidAppleMessupCarsLayouts = collectionView?.contentOffset
}
override func targetContentOffset(
forProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
if avoidAppleMessupCarsLayouts != nil {
return avoidAppleMessupCarsLayouts!
}
return super.targetContentOffset(forProposedContentOffset: proposedContentOffset)
}
}
So here are the three layouts for your "Cars" screen:
CarsLayout1: FixerForCarsLayouts { ...
CarsLayout2: FixerForCarsLayouts { ...
CarsLayout3: FixerForCarsLayouts { ...
That's it. It now works.
Incredibly obscurely, you could have different "sets" of layouts (for Cars, Dogs, Houses, etc.), which could (conceivably) collide. For this reason, have a global and a base class as above for each "set".
This was invented by passing user #Isaacliu, above, many years ago.
A detail, FWIW in Isaacliu's code fragment, finalizeLayoutTransition is added. In fact it's not necessary logically.
The fact is, until Apple change how it works, every time you animate between collection view layouts, you do have to do this. That's life!
This issue bit me as well and it seems to be a bug in the transition code. From what I can tell it tries to focus on the cell that was closest to the center of the pre-transition view layout. However, if there doesn't happen to be a cell at the center of the view pre-transition then it still tries to center where the cell would be post-transition. This is very clear if you set alwaysBounceVertical/Horizontal to YES, load the view with a single cell and then perform a layout transition.
I was able to get around this by explicitly telling the collection to focus on a specific cell (the first cell visible cell, in this example) after triggering the layout update.
[self.collectionView setCollectionViewLayout:[self generateNextLayout] animated:YES];
// scroll to the first visible cell
if ( 0 < self.collectionView.indexPathsForVisibleItems.count ) {
NSIndexPath *firstVisibleIdx = [[self.collectionView indexPathsForVisibleItems] objectAtIndex:0];
[self.collectionView scrollToItemAtIndexPath:firstVisibleIdx atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:YES];
}
Jumping in with a late answer to my own question.
The TLLayoutTransitioning library provides a great solution to this problem by re-tasking iOS7s interactive transitioning APIs to do non-interactive, layout to layout transitions. It effectively provides an alternative to setCollectionViewLayout, solving the content offset issue and adding several features:
Animation duration
30+ easing curves (courtesy of Warren Moore's AHEasing library)
Multiple content offset modes
Custom easing curves can be defined as AHEasingFunction functions. The final content offset can be specified in terms of one or more index paths with Minimal, Center, Top, Left, Bottom or Right placement options.
To see what I mean, try running the Resize demo in the Examples workspace and playing around with the options.
The usage is like this. First, configure your view controller to return an instance of TLTransitionLayout:
- (UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout
{
return [[TLTransitionLayout alloc] initWithCurrentLayout:fromLayout nextLayout:toLayout];
}
Then, instead of calling setCollectionViewLayout, call transitionToCollectionViewLayout:toLayout defined in the UICollectionView-TLLayoutTransitioning category:
UICollectionViewLayout *toLayout = ...; // the layout to transition to
CGFloat duration = 2.0;
AHEasingFunction easing = QuarticEaseInOut;
TLTransitionLayout *layout = (TLTransitionLayout *)[collectionView transitionToCollectionViewLayout:toLayout duration:duration easing:easing completion:nil];
This call initiates an interactive transition and, internally, a CADisplayLink callback that drives the transition progress with the specified duration and easing function.
The next step is to specify a final content offset. You can specify any arbitrary value, but the toContentOffsetForLayout method defined in UICollectionView-TLLayoutTransitioning provides an elegant way to calculate content offsets relative to one or more index paths. For example, in order to have a specific cell to end up as close to the center of the collection view as possible, make the following call immediately after transitionToCollectionViewLayout:
NSIndexPath *indexPath = ...; // the index path of the cell to center
TLTransitionLayoutIndexPathPlacement placement = TLTransitionLayoutIndexPathPlacementCenter;
CGPoint toOffset = [collectionView toContentOffsetForLayout:layout indexPaths:#[indexPath] placement:placement];
layout.toContentOffset = toOffset;
Easy.
Animate your new layout and collectionView's contentOffset in the same animation block.
[UIView animateWithDuration:0.3 animations:^{
[self.collectionView setCollectionViewLayout:self.someLayout animated:YES completion:nil];
[self.collectionView setContentOffset:CGPointMake(0, -64)];
} completion:nil];
It will keep self.collectionView.contentOffset constant.
If you are simply looking for the content offset to not change when transition from layouts, you can creating a custom layout and override a couple methods to keep track of the old contentOffset and reuse it:
#interface CustomLayout ()
#property (nonatomic) NSValue *previousContentOffset;
#end
#implementation CustomLayout
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
{
CGPoint previousContentOffset = [self.previousContentOffset CGPointValue];
CGPoint superContentOffset = [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
return self.previousContentOffset != nil ? previousContentOffset : superContentOffset ;
}
- (void)prepareForTransitionFromLayout:(UICollectionViewLayout *)oldLayout
{
self.previousContentOffset = [NSValue valueWithCGPoint:self.collectionView.contentOffset];
return [super prepareForTransitionFromLayout:oldLayout];
}
- (void)finalizeLayoutTransition
{
self.previousContentOffset = nil;
return [super finalizeLayoutTransition];
}
#end
All this is doing is saving the previous content offset before the layout transition in prepareForTransitionFromLayout, overwriting the new content offset in targetContentOffsetForProposedContentOffset, and clearing it in finalizeLayoutTransition. Pretty straightforward
If it helps add to the body of experience: I encountered this problem persistently regardless of the size of my content, whether I had set a content inset, or any other obvious factor. So my workaround was somewhat drastic. First I subclassed UICollectionView and added to combat inappropriate content offset setting:
- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated
{
if(_declineContentOffset) return;
[super setContentOffset:contentOffset];
}
- (void)setContentOffset:(CGPoint)contentOffset
{
if(_declineContentOffset) return;
[super setContentOffset:contentOffset];
}
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated
{
_declineContentOffset ++;
[super setCollectionViewLayout:layout animated:animated];
_declineContentOffset --;
}
- (void)setContentSize:(CGSize)contentSize
{
_declineContentOffset ++;
[super setContentSize:contentSize];
_declineContentOffset --;
}
I'm not proud of it but the only workable solution seems to be completely to reject any attempt by the collection view to set its own content offset resulting from a call to setCollectionViewLayout:animated:. Empirically it looks like this change occurs directly in the immediate call, which obviously isn't guaranteed by the interface or the documentation but makes sense from a Core Animation point of view so I'm perhaps only 50% uncomfortable with the assumption.
However there was a second issue: UICollectionView was now adding a little jump to those views that were staying in the same place upon a new collection view layout — pushing them down about 240 points and then animating them back to the original position. I'm unclear why but I modified my code to deal with it nevertheless by severing the CAAnimations that had been added to any cells that, actually, weren't moving:
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated
{
// collect up the positions of all existing subviews
NSMutableDictionary *positionsByViews = [NSMutableDictionary dictionary];
for(UIView *view in [self subviews])
{
positionsByViews[[NSValue valueWithNonretainedObject:view]] = [NSValue valueWithCGPoint:[[view layer] position]];
}
// apply the new layout, declining to allow the content offset to change
_declineContentOffset ++;
[super setCollectionViewLayout:layout animated:animated];
_declineContentOffset --;
// run through the subviews again...
for(UIView *view in [self subviews])
{
// if UIKit has inexplicably applied animations to these views to move them back to where
// they were in the first place, remove those animations
CABasicAnimation *positionAnimation = (CABasicAnimation *)[[view layer] animationForKey:#"position"];
NSValue *sourceValue = positionsByViews[[NSValue valueWithNonretainedObject:view]];
if([positionAnimation isKindOfClass:[CABasicAnimation class]] && sourceValue)
{
NSValue *targetValue = [NSValue valueWithCGPoint:[[view layer] position]];
if([targetValue isEqualToValue:sourceValue])
[[view layer] removeAnimationForKey:#"position"];
}
}
}
This appears not to inhibit views that actually do move, or to cause them to move incorrectly (as if they were expecting everything around them to be down about 240 points and to animate to the correct position with them).
So this is my current solution.
I've probably spent about two weeks now trying to get various layout to transition between one another smoothly. I've found that override the proposed offset is working in iOS 10.2, but in version prior to that I still get the issue. The thing that makes my situation a bit worse is I need to transition into another layout as a result of a scroll, so the view is both scrolling and transitioning at the same time.
Tommy's answer was the only thing that worked for me in pre 10.2 versions. I'm doing the following thing now.
class HackedCollectionView: UICollectionView {
var ignoreContentOffsetChanges = false
override func setContentOffset(_ contentOffset: CGPoint, animated: Bool) {
guard ignoreContentOffsetChanges == false else { return }
super.setContentOffset(contentOffset, animated: animated)
}
override var contentOffset: CGPoint {
get {
return super.contentOffset
}
set {
guard ignoreContentOffsetChanges == false else { return }
super.contentOffset = newValue
}
}
override func setCollectionViewLayout(_ layout: UICollectionViewLayout, animated: Bool) {
guard ignoreContentOffsetChanges == false else { return }
super.setCollectionViewLayout(layout, animated: animated)
}
override var contentSize: CGSize {
get {
return super.contentSize
}
set {
guard ignoreContentOffsetChanges == false else { return }
super.contentSize = newValue
}
}
}
Then when I set the layout I do this...
let theContentOffsetIActuallyWant = CGPoint(x: 0, y: 100)
UIView.animate(withDuration: animationDuration,
delay: 0, options: animationOptions,
animations: {
collectionView.setCollectionViewLayout(layout, animated: true, completion: { completed in
// I'm also doing something in my layout, but this may be redundant now
layout.overriddenContentOffset = nil
})
collectionView.ignoreContentOffsetChanges = true
}, completion: { _ in
collectionView.ignoreContentOffsetChanges = false
collectionView.setContentOffset(theContentOffsetIActuallyWant, animated: false)
})
This finally worked for me (Swift 3)
self.collectionView.collectionViewLayout = UICollectionViewFlowLayout()
self.collectionView.setContentOffset(CGPoint(x: 0, y: -118), animated: true)
Is there any way in which we can know if a UITableView is being scrolled in upward direction or downward direction?
-(void) scrollViewDidScroll:(UIScrollView *)scrollView
{
CGPoint currentOffset = scrollView.contentOffset;
if (currentOffset.y > self.lastContentOffset.y)
{
// Downward
}
else
{
// Upward
}
self.lastContentOffset = currentOffset;
}
-(void)scrollViewWillEndDragging:(UIScrollView *)scrollView
withVelocity:(CGPoint)velocity
targetContentOffset:(inout CGPoint *)targetContentOffset{
if (velocity.y > 0){
NSLog(#"up");
}
if (velocity.y < 0){
NSLog(#"down");
}
}
Could we do like this?
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if ([scrollView.panGestureRecognizer translationInView:scrollView].y > 0) {
// down
} else {
// up
}
}
UITableView is a UIScrollView subclass, thus you can set yourself as the UIScrollViewDelegate and get scroll view delegate callbacks.
The argument for one of these delegate methods (-scrollViewDidScroll:) is the scroll view that did scroll, you can compare it to your table views to know which one it was that scrolled.
Sorry, I misread your question. I thought you wanted to know which table view is being scrolled (I missed the "way").
To know the direction you can keep the previous offset in a variable and see if the delta (current.y - previous.y) is positive (scrolling down) or negative (scrolling up).
You can track the difference in content offset. Keep the old one in a member/static variable and check against the current. If the old value it's lower then the scrolling was directed downwards and vice versa.
override func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
if targetContentOffset.memory.y < scrollView.contentOffset.y {
//println("Going up!")
} else {
// println("Going down!")
}
}
You can do this by implementing UIScrollView's delegate method in this way, it's graceful.
PS: lastOffset and scrollingUpward is property of ViewController.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGPoint currentOffset = scrollView.contentOffset;
self.scrollingUpward = currentOffset.y > self.lastOffset.y;
self.lastOffset = currentOffset;
}
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
if (yourTableView.isDragging || yourTableView.isDecelerating)
{
// your tableview is scrolled.
// Add your code here
}
}
Here you have to replace your tableview name instead of "yourTableView".
yourTableView.isDragging - It returns YES if user has started scrolling. this may require some time and or distance to move to initiate.
yourTableView.isDecelerating - It returns YES if user isn't dragging (touch up) but scroll view is still moving.
Trying to achieve the look & feel of a Grouped TableView, with only one item per section, and but with hardly any margins (gives me rounded edged view with the ability for the user to be able to choose the color they want).
I have it working, HOWEVER when the user changes orientation I had to use the didRotateFromInterfaceOrientation method (as willRotateToInterfaceOrientation didn't work), BUT the effect is that you do see the margins change quickly in that fraction of a second after the tableView displays.
QUESTION - Any way to fix things so one doesn't see this transition?
- (void) removeMargins {
CGFloat marginAdjustment = 7.0;
CGRect f = CGRectMake(-marginAdjustment, 0, self.tableView.frame.size.width + (2 * marginAdjustment), self.tableView.frame.size.height);
self.tableView.frame = f;
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
[self removeMargins];
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation {
[super didRotateFromInterfaceOrientation:fromInterfaceOrientation];
[self removeMargins];
}
I Think the problem is that in willRotateToInterfaceOrientation the frame of the tableView hasn't resized yet, so your frame calculations are incorrect. on didRotateFromInterfaceOrientation the frame has already changed.
I think the easiest way to solve this is to subclass UITableView and override layoutSubviews. This method is called every time the frame of the view changes in a way that may require it's subviews to change.
The following code worked for me without an animation glitch:
#interface MyTableView : UITableView {
}
#end
#implementation MyTableView
-(void) layoutSubviews
{
[super layoutSubviews];
CGFloat marginAdjustment = 7.0;
if (self.frame.origin.x != -marginAdjustment) // Setting the frame property without this check will call layoutSubviews again and cause a loop
{
CGRect f = CGRectMake(-marginAdjustment, 0, self.frame.size.width + (2 * marginAdjustment), self.frame.size.height);
self.frame = f;
}
}
#end
You say that willRotateToInterfaceOrientation didn't work, but you didn't say why.
If the reason is that willRotateToInterfaceOrientation isn't being called, then please take a look at this question.
If you get this working then I believe your other question will solve itself.
I have a custom UITableViewCell with a UIScrollView in it that is wired to the cell controller. When I assign text to the scrollview, some cells get the correct text, some are blank, some redisplay old text and others have the scrollview clipped around the 2nd or 3rd line of text. It seems random on what will happen. I followed the suggestion here of using a timer to fix blank cells, http://www.bdunagan.com/2008/12/08/uitextview-in-a-uitableview-on-the-iphone/, but that didn't help. I placed the timer code in the cellForRowAtIndexPath method.
I've also tried calling
[cell.textview setNeedsDisplay];
after text is assigned to the textview but it doesn't have any affect.
When I use a textfield or label, everything looks fine. However, I need something that can scroll text. Any suggestions on a fix or better way?
Update: Found this on the dev forums (specifically mentions your problem):
https://devforums.apple.com/message/38944#38944
I would follow the link it has some more detailed info.
// view controller
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
NSArray* visibleCells = [self.tableView visibleCells];
for (UITableViewCell* cell in visibleCells)
{
if ([cell.reuseIdentifier isEqualToString:kTextViewCellID])
{
[(MTextViewCell*)cell refresh];
}
}
}
// MTextViewCell
- (void)refresh
{
// mucking with the contentOffset causes the textView to redraw itself
CGPoint contentOffset = mTextView.contentOffset;
CGPoint contentOffset1 = { contentOffset.x, contentOffset.y + 1.0f };
mTextView.contentOffset = contentOffset1;
mTextView.contentOffset = contentOffset;
}
Try calling:
[tableView reloadData];
After you update all the textViews.