I have a ScrollView that is supposed to be scrolled only downwards. The content View's size matches scrollview identically. I use this code to prevent from scrolling up:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
#define CONTENT_OFFSET 0
NSLog(#"%f", scrollView.contentOffset.y);
//prevent from scrolling up
if (scrollView.contentOffset.y > CONTENT_OFFSET) {
scrollView.contentOffset = CGPointMake(0, CONTENT_OFFSET);
}
}
It used to work perfectly. But now for some reason scroll view starts at -44 points and is of course scrollable up to 0. In between -44 and 0 it doesn't bounce if drag ended. I'm pretty sure I have not changed anything in layout but I might have unintentionally. I think scroll view now has bigger content view for some reason. Where do I look for the origin of this problem?
Related
I know that the sticky header is not a new thing to ask advice on, but still...
I am trying to create a sticky header (UIImageView) and the scrolling part (UIScrollView with a UIStackView in it)
Im using the scrollViewDidScroll method from the UIScrolLViewDelegate. The only problem is, that when I scroll the view up, I am not only decreasing the height of the header view, but also scrolling the content of the stack view. So when I scroll further up, you still can see the header view, but the top content of the scroll view disappears by scrolling.
Can this be solved somehow that when I scroll up, the content of the stack view is scrolling up and not also disappearing? And starts disappearing when the header view disappears?
Thank you
The easiest way to do this is to use a table view. Your sticky header is the table's first section header, while the scrolling part is the second section.
If you can't use a table, for whatever reason, then you have to mess around with the scroll view's content offset. When the contentOffset.y is growing (but not beyond your header's height), reset it to 0 and decrease the header's height accordingly. After the header's height is 0, stop messing with contentOffset - until you come back and the contentOffset.y wants to go into negatives.
P.S. the second solution requires you to enable bouncing on the scroll view. Otherwise, the header will be hidden, but won't show again (unless you reset the controller)
L.E. Some (old) code for my second solution:
let headerHeight = self.headerView.height
self.scrollHandler = {
var offset = self.detailsTable.contentOffset
self.headerTopConstraint.constant -= offset.y
if self.headerTopConstraint.constant < -headerHeight {
self.headerTopConstraint.constant = -headerHeight
let size = self.detailsTable.contentSize
if offset.y + self.detailsTable.frame.height > size.height {
offset.y = size.height - self.detailsTable.frame.height
}
self.detailsTable.contentOffset = offset
}
else {
if self.headerTopConstraint.constant > 0 {
self.headerTopConstraint.constant = 0
}
self.detailsTable.contentOffset = CGPointZero
}
}
Please note that my code moved the header upwards to hide it. As far as I understood, you just have to change the header's height (by the same amount I move it upwards).
I have a UIScrollView A (in fact a UICollectionView) filling the screen inside a UINavigationController B. The controller B's adjustScrollViewInsets is set to true.
I want to hide the navigation bar when user scrolls up, and show it when down. Following is my code:
func scrollViewDidScroll(scrollView: UIScrollView) {
if (self.lastContentOffset < scrollView.contentSize.height - scrollView.frame.size.height && self.lastContentOffset > scrollView.contentOffset.y) {
// dragging down
if self.navigationController!.navigationBarHidden {
self.navigationController?.setNavigationBarHidden(false, animated: true)
}
} else if (self.lastContentOffset > 0 && self.lastContentOffset < scrollView.contentOffset.y) {
// dragging up
if !self.navigationController!.navigationBarHidden {
self.navigationController?.setNavigationBarHidden(true, animated: true)
}
}
self.lastContentOffset = scrollView.contentOffset.y
}
Now the problem is, since the screen of iPhone 6+ is too large, the contentSize of the scroll view A is smaller than its frame(i.e. the full screen frame) when the navigation bar is hidden. In such circumstance, the scroll view will not be scrollable, and the navigation bar will never be back again.
I want to manually maintain the height of the contentSize of A to screen at least height + 1, but don't know how to do this. Could anyone help? Or provide a better solution?
BTW, I am using iOS 8 and Swift.
Lets say you need to keep the minimum content size of scroll view to 100(of course this will be dynamic and vary according to device)
NSInteger minScrollViewContentHeight = 100;
After populating the scroll view with content, you need to check if the scroll view's content size is less than minimum required scroll views content size. If its lesser than the required content size than you need to set the minimum content size of the scroll view as follows -
if(scrollView.contentSize.height < minScrollViewContentHeight)
[scrollView setContentSize:CGSizeMake(scrollView.frame.size.width, minScrollViewContentHeight)];
Off the top of my head (I'm on a phone), contentSize is not read-only I think.
How about changing it manually to the desired amount depending on the circumstances of scrolling direction etc?
Something like:
IF navbar is hidden THEN contentSize = whatever
An option would be to use the appearance and disappearance of cells to trigger the show/hide.
Use the delegate methods collectionView:willDisplayCell:forItemAtIndexPath: and collectionView:didEndDisplayingCell:forItemAtIndexPath: to detect movement. You can work out the direction from the index change of the cells being shown or removed. If you cannot scroll off screen then nothing happens.
You have to change no offset (which is actually just scrolling position), but contentSize itself. That means, that when you hide navigation bar, increase contentSize by navigation height (don't remember numbers) and when you show navigation bar, decrease contentSize. Or... Use AutoLayout and layoutIfNeeded method after showing/hiding navigation bar.
I stumbled upon a similar problem. I needed a minimum scrollable area for a tableview i was using.
ScrollView might be a bit easier since you can directly modify the contentView size.
If you're using autoLayout, try adding equal heights constraint between the contentView and the scrollView itself. Something along the lines of contentView.height = scrollView.height + scrollMin;
For my tableView i had to subclass UITableView and override the contentSize setter.
#define MIN_SCROLL 60
- (void)setContentSize:(CGSize)contentSize {
//take insets into account
UIEdgeInsets insets = self.contentInset;
CGFloat minHeight = self.frame.size.height - insets.top - insets.bottom + MIN_SCROLL;
if(contentSize.height < minHeight) {
contentSize.height = minHeight;
}
[super setContentSize:contentSize];
}
I have one UIImageView (building's floor map) and UIScrollView with gesture recognisers which allow me to scroll horizontally and vertically, zoom in/out. Everything works OK, but the building has two floors, so user should have the option to switch between them. I decided to use segmented control at the top of the map to provide this option.
If I put Segmented Control to the same UIScrollView, it scrolls vertically as well as horizontally. What I am asking is how to fix horizontal position of the Segmented Control, so it will be able to scroll only vertically with map.
I am trying to use this code to test, if it fixes the position of Segmented Control absolutely, but it seems to be that it doesn't.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
CGRect frame = _floorSelector.frame;
frame.origin.y=50;
frame.origin.x= 160;
_floorSelector.frame = frame;
}
Where is the mistake? Thank you for replies!
I think the issue here is you are misunderstanding how scrolling is implemented in a UIScrollView, and how things are placed in its coordinate space.
When a UIScrollView is scrolled, the frames of its subviews are not changed. Relative to the scrollview, they remain in the same position while the contentOffset and bounds of the scroll view changes. In order to make a subview of a scroll view appear static while the rest of it scrolls, you must change its frame within the scrollview as the bounds change.
With that in mind, what you are doing now is just setting the same frame on that subview repeatedly, which is the same as not doing anything.
It sounds like what you want to do is something like this:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
CGRect frame = _floorSelector.frame;
frame.origin.x = 160 + scrollView.contentOffset.x;
_floorSelector.frame = frame;
}
Notice I do not change anything in the y axis because based on your question, the vertical scrolling doesn't need to be changed.
So I realize that having nested scroll views at all it sort of a red flag, but the current setup of everything actually works quite well besides one small problem. One scroll view manages scrolling through a collection, while another handles zooming and panning on the entire collection view. This all works, but the small problem comes from when zooming in and panning downward, the scrollview pans while the collectionview scrolls, causing the view to scroll twice as fast, and not feel connected to your finger.
What I ideally want to happen is vertical scrolling is managed by the outer scroll view when panning is possible, and then handled by the inner scroll view when the outer one can no longer pan. I got very close by writing something like this:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if (scrollView == _outerScrollView) {
CGPoint offset = _outerScrollView.contentOffset;
CGFloat height = _outerScrollView.frame.size.height;
CGFloat contentHeight = _outerScrollView.contentSize.height;
ScrollDirection scrollDirection;
if (offset > _lastContentOffset){
scrollDirection = ScrollDirectionUp;
} else {
scrollDirection = ScrollDirectionDown;
}
BOOL scrollIsAtTop = offset.y <= 0;
BOOL scrollIsAtBottom = offset.y + height >= contentHeight;
//If there is a pan upward and we aren't at the top of the outer
//scrollview cancel the gesture on the inner view
//downward vice versa
if (!((scrollIsAtTop && scrollDirection == ScrollDirectionUp)
|| (scrollIsAtBottom && scrollDirection == ScrollDirectionDown))) {
_innerCollectionView.panGestureRecognizer.enabled = NO;
_innerCollectionView.panGestureRecognizer.enabled = YES;
}
}
_lastContentOffset = offset.y;
}
This ALMOST works, with one side effect of a big pan downward stops when it hits the bottom and requires the user to start a new gesture to continue scrolling with the inner collection. Ideally this transition would be smooth, but I'm having a hard time figuring out a way to do this. Again I realize scroll view inside scroll view is not ideal, but if I can fix this small problem everything will be good, rather than attempt to redesign the whole thing.
Any ideas on how I can handle the double scroll in a way that lets the pan gesture win, but cleanly transitions to the inner collection when the outer scroll view can no longer pan vertically?
So, since I never got any answers, this is the solution I've been going with. Essentially if the inner collection view isn't at the top or bottom, I reset the y offset change the outer scroll view has in scrollViewDidScroll. Code looks like this:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if (scrollView == _outerScrollView) {
if (![self innerScrollIsAtTop] && ![self innerScrollIsAtBottom] && !self.allowOuterScroll) {
[scrollView setContentOffset:CGPointMake(scrollView.contentOffset.x, self.lastContentOffset)];
}
self.lastContentOffset = scrollView.contentOffset.y;
}
}
using these 2 conveniences:
- (BOOL)innerScrollIsAtTop {
return _innerCollectionView.contentOffset.y <= 0;
}
- (BOOL)innerScrollIsAtBottom {
CGFloat zoom = self.zoomScale;
CGFloat height = _innerCollectionView.frame.size.height;
CGFloat contentHeight = _innerCollectionView.contentSize.height;
CGPoint offset = _innerCollectionView.contentOffset;
return offset.y + height / zoom >= contentHeight;
}
And you'll need 2 class variables, a float to hold the previous y content offset of the outer scroll, and a BOOL to hold whether you want to allow the outer scroll view to scroll, which you can set to YES while zooming or programatically scrolling. This solution fixes the double scroll, but does have a cumbersome hack within scrollviewDidScroll that may bite you later and you constantly need to work around, but for now this is the solution I've been using.
Forgive me to the obtuse title, as I'm unsure how to describe this question.
Recently many iOS apps utilise a scrolling UI design pattern which helps to maximise screen real-estate, typically hiding the header when the user scrolls downwards.
For example, Instragram's main view has the Instragram header at the top. Scrolling upwards on this view keeps the header fixed at the top, and the view bounces back normally to the top of the content. But scroll down and the header acts as part of the content, making way for an extra 44 points of vertical space.
Its probably that I haven't done much iOS work in a while, but I can't easily figure out how best to impliment this? Apologies for the terrible description.
If the header stays put no matter what, use a separate view on top of the scroll view.
If you use UITableView, you can use section headers.
EDIT Use this code:
- (void)scrollViewDidScroll:(UIScrollView*) scrollView
{
CGPoint offset = scrollView.contentOffset;
CGRect headerFrame = _headerView.frame;
if(offset.y > 0){
headerFrame.origin.y = offset.y;
}
else{
headerFrame.origin.y = 0.0;
}
[_headerView setFrame:headerFrame];
}
(Assumes _headerView is your header, sitting on top of the scroll view, not inside it. Also, both scroll view and header begin at the top of their parent view, y==0. Also, your view controller must be set up as delegate of the scroll view)
I just wrote this code from memory; haven't tested it but at most it should only need tweaking.
I tried ranReloaded's answer above but it seems that calling setFrame: on a UIScrollView stops the view from bouncing when going beyond its bounds.
Instead I set the scroll view to fit inside another UIView called scrollerWrapper. Applying the calculated origin and height to this view gives me effect I'm after plus retains the bounce behaviour.
- (void)scrollViewDidScroll:(UIScrollView*) scrollView
{
CGPoint offset = scrollView.contentOffset;
CGRect headerFrame = header.frame;
CGRect wrapperFrame = scrollerWrapper.frame;
if(offset.y > 0){
headerFrame.origin.y = -offset.y;
wrapperFrame.origin.y = MAX(0, headerFrame.size.height - offset.y);
}
else{
headerFrame.origin.y = 0.0;
wrapperFrame.origin.y = headerFrame.size.height;
}
wrapperFrame.size.height = self.view.frame.size.height - wrapperFrame.origin.y;
[header setFrame:headerFrame];
[scrollerWrapper setFrame:wrapperFrame];
}