I am working with aUIScrollview, and based on if the user scrolls left or right, I reconfigure the UI. The problem is that I need to verify that the user definitely crossed from one screen to another (something along contentOffset).
I've tried using this method:
-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;
But this will fire if the user kind of moves the scrollview partially in one direction, but then doesn't complete the gesture.
I've also tried this method:
-(void)scrollViewDidScroll:(UIScrollView *)scrollView;
but mainly the same issue; the scrollview scrolls left and right, but on an iPhone, with a content with of 640 ( 320 * 2). I am trying to figure out if the scroll did cross over or not, from one location to the other.
Any suggestions?
I am not entirely sure what you mean by "crossed from one screen to another" I assume you mean paging? If so, here's what you can do:
- (void)scrollViewDidEndDecelerating:(UIScrollView *)sender {
int page = sender.contentOffset.x / width;
[self.pageControl setCurrentPage:page]; // in case you need it for updating a UIPageControl
}
I found a way of doing this :
I have a variable to maintain the x location of the contentOffset
-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
currX = self.scrollView.contentOffset.x;
}
And then in this event :
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
if(self.scrollView.contentOffset.x == currX ) {
return;//This is what I needed, If I haven't panned to another view return
}
//Here I do my thing.
Related
How would you go about implementing a UICollectionView with this behaviour?
The idea is that once a user navigates past a certain point, they cannot go back and view those cells again.
My attempt at a solution has been to listen for gestures on the collection view and if disable scrolling once a swipe occurs on the element. The obvious problem with this is that the user can simple hold and drag any particular cell.
Any thoughts?
I think this behavior may be confusing for your users.
Maybe you should try to add some elasticity/bouncing so that your users would be less confused.
Anyway, I see two different ways to achieve this without subclassing
1/ Since UICollectionViewDelegate conforms to UIScrollViewDelegate, you can get the starting offset of your scrollview with – scrollViewWillBeginDragging: then in – scrollViewDidScroll: you would compare the new offset's x value. If the new offset.x 's value is smaller than the starting one, set it to 0 and update your scrollview.
#pragma mark - UIScrollViewDelegate
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
offset = scrollView.contentOffset;
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGPoint newOffset = scrollView.contentOffset;
if (newOffset.x < offset.x) {
// scrolling to the left, reset offset
[scrollView setContentOffset:offset];
}
}
Because there is inertia with scrolling in iOS, scrollViewDidScroll: is called a lot of time, so it may cause performance issues. You may reduce the number of call by targeting your offset with scrollViewWillEndDragging:withVelocity:targetContentOffset: from UIScrollViewDelegate.
2/ Or ou can just use the method scrollViewWillEndDragging:withVelocity:targetContentOffset: which I just spoke about, which sets the offset back to its beginning, with an animation.
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
CGPoint newOffset = scrollView.contentOffset;
if (newOffset.x < offset.x) {
// scrolling to the left, reset offset with animation
targetContentOffset->x = offset.x;
}
}
3/ You spoke of UISwipeGestureRecognizer, did you give a try to UIPanGestureRecognizer? This is what "simple hold and drag" is.
You can implement it the same way you would implement an infinite scroll view, by adding / removing items based on the scroll offset.
Override the viewDidScroll: method (UICollectionViewDelegate)
Check if your offset puts the first object of your list past the offset (ie. can you still see it on the screen?)
If it is, then remove it from the collection view.
This simple implementation might result in choppy animations, you might have to do some optimization once it's working but this should get you started.
Another possible solution would be to "reposition" all your elements constantly to appear where they were before you started scrolling if you are scrolling left.
You can achieve this by keeping track of the highest offsetX you ever encountered, and reposition your cells if the current offsetX is lower than the max. That way you will have the impression that your cells are not moving or that you can't scroll, but you will actually be scrolling.
In my case, I have a paginated collection view, so I have to take care when decelerating in the last item of the collection view as well in automatic decelerations for each page.
To fix the issue, I just disable user interaction while the collection view is "moving automatically".
Here the code:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
if (!_isDragging) // <-- only do things if the user is dragging!
return;
CGPoint contentOffset = scrollView.contentOffset;
// If we move to the left
if (contentOffset.x < _contentOffset.x)
{
CGSize contentSize = scrollView.contentSize;
// If content offset is moving inside contentSize:
if ((contentOffset.x + scrollView.bounds.size.width) < contentSize.width)
scrollView.contentOffset= _contentOffset;
}
else
{
// Update the current content offset
_contentOffset = contentOffset;
}
}
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
_isDragging = YES;
}
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
_isDragging = NO;
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
if (decelerate)
{
// If willDecelerate, stop user interaction!
_collectionView.userInteractionEnabled = NO;
}
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
// Once deceleration is finished, enbale user interaction
_collectionView.userInteractionEnabled = YES;
// Set the new content offset
_contentOffset = scrollView.contentOffset;
}
I have a screen which has two UIScrollViews. Inside the scrollview is a zoomable UIImageView.
I'd like to achieve the same scrolling and zooming inside one scrollView to be applied to the other one. i.e. if the user pans across the image, both scrollviews pan their images at the exact same rate. If the user pinch zooms the image in one, the other zooms exactly the same amount.
I've read on here about using the zoomToRect:animated: call. I'm not sure exactly how to implement that, so I've tried the following - but it doesn't seem to yield the right results. NB. the scrollView contain self.imageViewLeft. self.scrollViewRight is the scrollView not being touched.
- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
CGRect visibleRect = [scrollView convertRect:scrollView.bounds toView:self.imageViewLeft];
[self.scrollViewRight zoomToRect:visibleRect animated:false];
}
I solved it guys! Props to me.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if (scrollView == self.scrollViewLeft) {
[self.scrollViewRight setZoomScale:[scrollView zoomScale]];
[self.scrollViewRight setContentOffset:[scrollView contentOffset]];
} else {
[self.scrollViewLeft setZoomScale:[scrollView zoomScale]];
[self.scrollViewLeft setContentOffset:[scrollView contentOffset]];
}
}
im atempting to do a facebook type load more data and right now it works, but very laggy on the device because its asking the server to get anything that isnt there already, then calling a scroll all the way down function (because somehow when i reload the data it scrolls to the top). If there would be a way to prevent scrolling to the top that would be great. But my main thing is, is there a way to detect when i scrolled down, and LET GO (stopped scrolling) as in i scrolled past what i have, then it went back to its possition and then calls my methods... Currently it keeps getting called when the scroll is greater then the height of the UITableView heres the code
-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
CGFloat height = scrollView.frame.size.height;
CGFloat contentYoffset = scrollView.contentOffset.y;
CGFloat distanceFromBottom = scrollView.contentSize.height - contentYoffset;
if(distanceFromBottom < height)
{
[getMessage removeAllObjects];
[self loadMessages];
[self.tableView reloadData];
[self scrollAllTheWayDown];
}
}
UIScrollViewDelegate method
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;
does what you want. it gets called after user stops scrolling, and you can check for scrollOffset at that point to see if you should trigger your refresh code. (you'd use scrollViewDidScroll to update the view to show user update will happen if he lets go)
I want to revert my UIScrollView's content offset if I don't drag enough:
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(CGPoint *)targetContentOffset {
self.endingOffset = scrollView.contentOffset;
if(abs(verticalOffset) > [self cellHeight] / 9) { // If the user scrolled enough distance, attempt to scroll to the next cell
...
} else if(self.nextCellOrigin.y != 0) { // The scroll view is still scrolling and the user didn't drag enough
...
} else { // If the user didn't drag enough
self.tableView.decelerationRate = UIScrollViewDecelerationRateNormal;
(*targetContentOffset) = self.startingOffset;
}
}
The code to revert to the original position is in the else portion, and it always works. However, when I don't scroll enough and make the gesture quickly, it snaps back. If I scroll just a little and then hold that position for slightly longer than usual, it reverts back smoothly.
I haven't found anything in the API reference for how long a user has touched a UIScrollView, and even if I did it's not immediately obvious how I could use that to change the behavior of my reverting code. I've also tried scrolling to the position with setContentOffset:animated: but that doesn't seem to fix the jerkiness.
Any ideas?
Have you tried logging the velocity to find out how it is when the jerkiness happens?
EDIT:
What you can try to do is implement these two scrollView delegate methods instead of the willEndDragging method. This solution will give a different feeling to the scrollView, but give it a try.
Fill the checkOffset method with all the logic you need.
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
// if scrollView's contentOffset reached its final position during scroll, it will not decelerate, so you need a check here too
if (!decelerate) {
[self checkOffset];
}
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
[self checkOffset];
}
- (void)checkOffset {
CGPoint newOffset;
...
// Do all the logic you need to move the content offset, then:
...
[self.scrollView setContentOffset:newOffset animated:YES];
}
EDIT #2:
Maybe you could achieve a better result if you also add this to my solution.. Try ;)
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(CGPoint *)targetContentOffset {
// This should force the scrollView to stop its inertial deceleration, by forcing it to stop at the current content offset
*targetContentOffset = scrollView.contentOffset;
}
How can I force a UIScrollView in which paging and scrolling are on to only move horizontally left or horizontally both direction(left and right)?
To be clearer, I'd like to allow the user to 'page only horizontally backward(only bounce when the user try to scroll horizontally right)' OR 'horizontally both direction(this is normal action)' at a given moment.
I am wondering that the solution is the subclass of UIScrollView.
Thanks in advance.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if ( only bounce.. ){
// is it right?
if (scrollView.contentOffset.y > 60) {
[scrollView setContentOffset:CGPointMake(0, 60)];
}
}
if ( only paing left... ){
How to do this??
}
}
I'd implement the delegate function scrollViewDidScroll: and store the state (scroll state) of the ScrollView. On subsequent calls, compare with the previous state and have it bounce back (by calling ZoomToRect: maybe) if it is in a particular direction that you don't like.