How do I navigate to a specific page programmatically. Basically I have an app with a scrollView populated with a bunch of subviews (tableViews in this case). When clicking on a subview it zooms in and the user can edit and navigate the table, however when I zoom back out I reload the entire view in case there were any changed made by the user. Of course reloading the view sends the user back to page 0. I've tried setting the pageControl.currentpage property but all that does is change the dot of the pageControl. Does that mean that something is wrong or do I need to do something else as well??
All that is controlling the page scrolling is this method:
- (void)scrollViewDidScroll:(UIScrollView *)sender
{
CGFloat pageWidth = self.scrollView.frame.size.width;
int page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
self.pageControl.currentPage = page;
NSString *listName = [self.wishLists objectAtIndex:self.pageControl.currentPage];
self.labelListName.text = listName;
}
You have to calculate the corresponding scroll position manually. To scroll to page i:
[scrollView setContentOffset:CGPointMake(scrollView.frame.size.width*i, 0.0f) animated:YES];
Swift 5 you can easily use scrollView.scrollRectToVisible
If the Horizontal paging scroll view implemented, which has the size of default view width of the device and wanted to navigate to number n page:
scrollView.scrollRectToVisible(CGRect(x: self.view.center.x * n, y: self.view.center.y, width: self.view.frame.width, height: self.view.frame.height) ,animated: true)
You just have to define the CGRect() position according to your scrollview configurations.
Swift 5 version of above answer by Ole Begemann
scrollView.setContentOffset( CGPoint(x: scrollView.frame.size.width * i, y: 0.0), animated: true)
Related
I am using UICollectionView to display photos in sections. Each section has a supplementary view as a header and is supplied via the method: viewForSupplementaryElementOfKind.
I have a scrubber on the side that allows the user to jump from section to section. For now I am scrolling to the first item in the section using scrollToItemAtIndexPath:atScrollPosition:animated:, but what I really want is to scroll the collectionView so that that section's header is at the top of the screen, not the first cell. I do not see an obvious method to do this with. Do any of you have a work around?
I suppose I could scroll to the first item of the section, and then offset that by the supplementary height plus the offset between the items and header if it comes down to that (there is a method for scrolling to point coordinates of the contentView). However if there is a simpler way, I'd like to know.
Thanks.
You can not use scrollToItemAtIndexPath:atScrollPosition:animated for this.
Hopefully, they will add a new method like scrollToSupplementaryElementOfKind:atIndexPath: in the future, but for now, the only way is to manipulate the contentOffset directly.
The code below shows how to scroll header to be on top vertically with FlowLayout. You can do the same for horizontal scrolling, or use this idea for other layout types.
NSIndexPath *indexPath = ... // indexPath of your header, item must be 0
CGFloat offsetY = [collectionView layoutAttributesForSupplementaryElementOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath].frame.origin.y;
CGFloat contentInsetY = self.contentInset.top;
CGFloat sectionInsetY = ((UICollectionViewFlowLayout *)collectionView.collectionViewLayout).sectionInset.top;
[collectionView setContentOffset:CGPointMake(collectionView.contentOffset.x, offsetY - contentInsetY - sectionInsetY) animated:YES];
Note that if you have non-zero contentInset (as in iOS 7, when scroll views expand below bars) you need to subtract it from the offsetY, as shown. Same for sectionInset.
Update:
The code assumes that the layout is in prepared, "valid" state because it uses it to calculate the offset. The layout is prepared when the collection view presents its content.
The call to [_collectionView.collectionViewLayout prepareLayout] before the code above may help when you need to scroll the collection view which is not yet presented (from viewDidLoad say). The call to layoutIfNeeded (as #Vrasidas suggested in comments) should work too because it also prepares the layout.
Solution in Swift,
let section: Int = 0 // Top
if let cv = self.collectionView {
cv.layoutIfNeeded()
let indexPath = IndexPath(row: 1, section: section)
if let attributes = cv.layoutAttributesForSupplementaryElement(ofKind: UICollectionView.elementKindSectionHeader, at: indexPath) {
let topOfHeader = CGPoint(x: 0, y: attributes.frame.origin.y - cv.contentInset.top)
cv.setContentOffset(topOfHeader, animated: true)
}
}
Props to Gene De Lisa: http://www.rockhoppertech.com/blog/scroll-to-uicollectionview-header/
// scroll to selected index
NSIndexPath* cellIndexPath = [NSIndexPath indexPathForItem:0 inSection:sectionIndex];
UICollectionViewLayoutAttributes* attr = [self.collectionView.collectionViewLayout layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:cellIndexPath];
UIEdgeInsets insets = self.collectionView.scrollIndicatorInsets;
CGRect rect = attr.frame;
rect.size = self.collectionView.frame.size;
rect.size.height -= insets.top + insets.bottom;
CGFloat offset = (rect.origin.y + rect.size.height) - self.collectionView.contentSize.height;
if ( offset > 0.0 ) rect = CGRectOffset(rect, 0, -offset);
[self.collectionView scrollRectToVisible:rect animated:YES];
One thing the solutions don't manage is if you are pinning section headers. The methods work fine with unpinned headers, but if your headers are pinned, while scrolling to a section above the current section, it will stop once the section header appears (which will be for the bottom row of your section). That may be desirable in some cases but I think the goal is to put the top of the section at the top of the screen.
In which case you need to take the methods above and adjust them a bit. For instance:
UICollectionView *cv = self.collectionView;
CGFloat contentInsetY = cv.contentInset.top;
CGFloat offsetY = [cv layoutAttributesForItemAtIndexPath:ip].frame.origin.y;
CGFloat sectionHeight =
[cv layoutAttributesForSupplementaryElementOfKind:UICollectionElementKindSectionHeader atIndexPath:ip].frame.size.height;
[cv setContentOffset:CGPointMake(cv.contentOffset.x, offsetY - contentInsetY - sectionHeight) animated:YES];
Now you are basically scrolling the first row of your section to visible, less the height of its section header. This will put the section header on the top where you want it with pinned headers so the direction of the scroll won't matter anymore. I didn't test with section insets.
I've got a VC with a table view. When an event occurs, I want to drop in a UIView from the top of the main view. When the user scrolls the table view, I want to re-layout the view so that the dropped in view "scrolls away". I figured I'd do this by moving the upperView's frame and resizing the table view (both in relation to the scroll offset). I've got it almost working as follows:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGFloat contentOffsetY = scrollView.contentOffset.y;
if (contentOffsetY > 0) {
CGFloat upperHeight = self.upperView.frame.size.height;
CGFloat fullTableHeight = self.view.frame.size.height;
CGFloat offsetY = (contentOffsetY < upperHeight)? -scrollView.contentOffset.y : -upperHeight;
self.upperView.frame = CGRectMake(0, offsetY, 320, upperHeight);
scrollView.frame = CGRectMake(0, upperHeight+offsetY, 320, fullTableHeight-(upperHeight+offsetY));
}
NSLog(#"%f", self.upperView.frame.origin.y);
}
The upper view origin starts at 0,0.
The problem is, after a little dragging back and forth, I lose the top few pixels of that upper view. It can't seem to get it's origin y back to zero. The logging reads negative values, and only gets to -1, with the most careful dragging. Has anybody done something like this? Much obliged if you can help.
It sounds like you always scroll the table view to the top when you show the drop-in view. Assuming that's the case, there is a better way to do this.
UITableView inherits the contentInset property from UIScrollView. The contentInset property defines a border on each edge of the scroll view. Each border has its own thickness, which is zero by default. These borders just affect how far the scroll view is willing to let the user scroll the content - they don't hide the content! If you set the top inset larger than zero, and give the scroll view a subview with a negative Y origin, that subview can be visible in the border, and will scroll with the rest of the scroll view's content.
So we'll set the table view's top inset to the height of the drop-in view, and add the drop-in view as a subview of the table view with its origin set to the negative of its height. This will make it fit perfectly on the screen above the first row of the table view, and it will scroll with the table view. When we detect that the drop-in view has been scrolled fully off-screen, we can just remove it from the table view and set the table view's top inset back to zero.
We'll need an instance variable that tracks the current state of the drop-in view:
typedef enum {
DropInViewStateHidden,
DropInViewStateAppearing,
DropInViewStateVisible
} DropInViewState;
#implementation ViewController {
DropInViewState _dropInViewState;
}
In my test project, I just used a button to trigger the drop-in view. Here's the action:
- (IBAction)dropIn {
if (_dropInViewState != DropInViewStateHidden)
return;
CGRect frame = self.dropInView.frame;
frame.origin.y = -frame.size.height;
self.dropInView.frame = frame;
[self.tableView addSubview:self.dropInView];
self.tableView.contentInset = UIEdgeInsetsMake(frame.size.height, 0, 0, 0);
[self.tableView setContentOffset:frame.origin animated:YES];
_dropInViewState = DropInViewStateAppearing;
}
When the table view scrolls, we check the state of the drop-in view. If it is in the “visible” state and has been scrolled off-screen, we hide it. There's a tricky bit because when we make the drop-in view visible, and scroll it onto the screen, we can receive scrollViewDidScroll: messages that would make us think the drop-in view has been hidden. That's why we start out in the DropInViewStateAppearing state, and transition to the DropInViewVisible state when we know the view has appeared.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
switch (_dropInViewState) {
case DropInViewStateHidden:
break;
case DropInViewStateVisible:
if (scrollView.contentOffset.y >= 0) {
// dropInView has been scrolled off-screen
self.tableView.contentInset = UIEdgeInsetsZero;
[self.dropInView removeFromSuperview];
_dropInViewState = DropInViewStateHidden;
break;
}
case DropInViewStateAppearing:
// When I first add dropInView to tableView and tell tableView
// to scroll to reveal dropInView, I may get a bunch of
// scrollViewDidScroll: messages with contentOffset.y >= 0.
// I don't want those messages to hide dropInView, so I sit in
// DropInViewStateAppearing until contentOffset.y goes negative,
// which means at least part of dropInView is actually on-screen.
if (scrollView.contentOffset.y < 0)
_dropInViewState = DropInViewStateVisible;
break;
}
}
Figured this out: The UITableView doesn't thoroughly message didScroll during the bounce. This is why I was missing a few pixels. Resizing during the bounce makes the bounce get mixed up and stop. This fix on my code above allows the bounce to work (by moving, not resizing the table) and makes sure the upper view is correctly placed during the bounce (when contentOffset.y <= 0).
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGFloat contentOffsetY = scrollView.contentOffset.y;
CGFloat upperHeight = self.upperView.frame.size.height;
CGFloat fullTableHeight = self.view.frame.size.height;
CGFloat offsetY = (contentOffsetY < upperHeight)? -scrollView.contentOffset.y : -upperHeight;
if (contentOffsetY > 0) {
self.upperView.frame = CGRectMake(0, offsetY, 320, upperHeight);
scrollView.frame = CGRectMake(0, upperHeight+offsetY, 320, fullTableHeight-(upperHeight+offsetY));
} else {
self.upperView.frame = CGRectMake(0, 0, 320, upperHeight);
scrollView.frame = CGRectMake(0.0, upperHeight, 320, scrollView.frame.size.height);
}
[super scrollViewDidScroll:scrollView];
}
Is there a way that I can use those paging dots independently in my app,
add them to my UIView/NIB and call the functions on it to set total number of dots or current page/dot.
Basically I've UIViewImage in a nib file, i'm displaying images (names taken off an array) on swipe gestures and want to show those paging dots on the bottom for the navigation information.
UIPageControl has it's total page & current page/dot just as you described, let's say pageControl is a instance of UIPageControl, then you can initiate the numberOfPages & currentPage as below:
pageControl.numberOfPages = [images count];
pageControl.currentPage = 0;
Also, you can add action for it when the pageControl's dots was tapped. changePage: method here is just a example:
[pageControl addTarget:self action:#selector(changePage:) forControlEvents:UIControlEventValueChanged];
You can add your images to a UIScrollView and use its delegate method: scrollViewDidScroll::
- (void)scrollViewDidScroll:(UIScrollView *)sender {
// Update the page number
CGFloat pageWidth = scrollView.frame.size.width;
pageControl.currentPage = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
}
It'll change the pageControl's current dot when your swiped to a new image.
I'm a beginner when it comes to page control, and that's why I'm not sure 100% if my title agrees with what I want. I want to make a UIPageControl that when the user swipes on the screen, the view would switch over to another view and the UIPageController at the bottom of the screen would update itself. Also, to make my request even more confusing, I want a tab bar at the bottom of the screen that would stay put as the views change.
A great example of this is The Iconfactory's Ramp Champ:
http://img.slidetoplay.com/screenshots/ramp-champ_5.jpg
The bar at the bottom stays put while the rest of the items on the screen moves. What would be the easiest way to do this?
EDIT: I know I have to use a UISrollView, I just don't know how to go about implementing it...
I believe what you're looking for is actually a UIScrollView with pagingEnabled set to YES. You can leave the scrollview as a view above a regular UITabBar. You'll use a UIPageControl to get the little dots. You can update it programmatically when the UIScrollView scrolls to a page by implementing an appropriate delegate method of the scroll view, maybe -scrollViewDidScroll:.
Assume you have two ivars: scrollView and pageControl. When you know how many pages your scroll view will have, you can set the contentSize of scrollView. It should be a multiple of the scrollView's bounds. For example, if the number of pages is static you can hardcode it in your -viewDidLoad...
- (void)viewDidLoad {
// Any other code.
scrollView.pagingEnabled = YES;
scrollView.contentSize = CGSizeMake(scrollView.bounds.size.width * 3, scrollView.bounds.size.height); // 3 pages wide.
scrollView.delegate = self;
}
Then, to update your little dots...
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGFloat pageWidth = scrollView.bounds.size.width;
NSInteger pageNumber = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
pageControl.currentPage = pageNumber;
}
You need to use a UIScrollView
Assuming you have a named ivar called scrollView
int amountOfFrames = 10;
scrollView.pagingEnabled = TRUE;
scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * amountOfFrames, scrollView.frame.size.height);
scrollView.delegate = self;
You will then need to implement the required delegate methods, so that you can update your page control
- (void)scrollViewDidScroll:(UIScrollView *)sender
{
// Switch the indicator when more than 50% of the previous/next page is visible
CGFloat pageWidth = scrollView.frame.size.width;
int page = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
pageControl.currentPage = page;
}
You need to place whatever content you want to be scrollable inside these scrollview, ideally lazyload into it, if the content you will displaying will require a lot of heap memory, use the scrollviewDidScroll to remove and add content at the required positions
If I've got a uiscrollview which is five pages wide, what code would tell me what page I am on, when I scroll to a new page? Also, what code would scroll to a specific page?
Thanks!
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
CGFloat pageWidth = scrollView.frame.size.width;
int currentPage = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
pageControl.currentPage = currentPage;
}
I have the scrollview frame width as the page width. If you are using something else as page width, make respective changes to get this to work
for scrolling to current page - if I understand it right, you have an option to enter page number and choose to scroll to that page:
Just the code above, do it reverse order, and solve for contentOffset.X
once you have the x value, create a frame with that x in it, and scrollToRect: animated: will do the work.
Check out the PageControl example from Apple:
http://developer.apple.com/iphone/library/samplecode/PageControl/Listings/ReadMe_txt.html
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
CGFloat scroller_x = [scrollView contentOffset].x;
CGFloat scroller_y = [scrollView contentOffset].y;
NSLog(#"%f, %f",scroller_x,scroller_y);
}
Once this delegate method fires (on scroll) check it against each views frame.origin.x and frame.origin.y The view's frame that matches will be the view that you scrolled to.
[scrollView setContentOffset:<#(CGPoint)#>];
use this method to scroll to a specific view.frame.origin. So suppose you have an action to go to a specific view, you can use [scrollView setContentOffset:view.frame.origin] to get there.
(assumed paging is enabled)