I have an app with a horizontal scrolling uiscrollview, it shows 3 subviews side by side. I am using Objective C.
When the user drags and releases, the code detects which is the closest subview and automatically scrolls to the nearest of the 3 subviews, making it fully centred.
This all works fine, except;
When the scrollview is animating an auto-centering move, the user can interrupt by just tapping it (not dragging).
This single tap halts the animation and scrollview, leaving it not centred on any of the 3 subviews.
No delegate method I have found can detect when the animation is interrupted and then continue with centering.
How can I do this?
When you start the scroll animation with setContentOffset:animated: or scrollToRectVisible:animated:, its end will be marked by UIScrollViewDelegate method scrollViewDidEndScrollingAnimation:. If before that other delegate method is called, like scrollViewWillBeginDragging: or scrollViewDidEndDecelerating: - that means that user interrupted your animatin with drag (or a tap).
What you want to do is restart your animation when user stops dragging - in scrollViewDidEndDragging:willDecelerate: or scrollViewDidEndDecelerating:
Thanks again mag_zbc!
This really helped me find the solution.
I was overcomplicating the animation, checking for the current position both after the user finished dragging as well as when the animation finished.
To solve it, I just checked the current offset in scrollViewDidEndDecelerating::
-If the final offset was one of the three correct locations (auto-offset finished uninterrupted) then do nothing.
-If the offset was not one of the correct locations (animation was interrupted), then move again.
Related
I am struggling with aligning a screen to a certain Views inside a UIScrollView. I would like to have same behaviour as paging (same fast and smooth deceleration) but with alignment to a custom views instead of stoping on multiples of the scroll view’s bounds. I have implemented delegate method scrollViewWillEndDragging(_:withVelocity:targetContentOffset:) in order to define my own scroll view’s bounds location. I have also set decelerationRate to UIScrollViewDecelerationRateFast.
It work mostly as desired except the cases when alignment animation is very slow. To be more precise, sometimes, after the dragging is finished, the scrolling animation decelerates to final point very slowly. It finally reach the correct point but after a longer while. I am not able to track down the cases when it happens. I am able to say that everything works fine when final velocity of dragging is zero. Thus, it happens only in some cases when dragging is finished with nonzero velocity.
I wonder if somebody had same problem since I wasn't able to google anything useful. Can you help me please?
I have solved this problem by implementing delegate methods scrollViewDidEndDragging and scrollViewWillBeginDecelerating. Then by using information from scroll view’s pan gesture I found out about translation and I determined final scroll view’s bounds location using setContentOffset method on scroll view.
I'm coding an ios application and the basic View is a UIMapView.
On the UIMapView I have a UIImageView.
I want this UIImageView's initial state to animate up and down on repeat on the screen. When a user pans across the map I would like the animation to continue. However, when the user stops panning, I would like the animation to stop. The animation should continue whenever the user pans across the screen and stop again when the user stops touching the screen.
Any ideas on how to do this?
Thanks so much!
I have a UIScrollView with no vertical scrolling, and on which I force a particular offset (only x) in case the offset tries to become less that that particular offset.
I use setContentOffset:animated: function, with animated argument as YES. The offset is forced correctly.
After I force the offset, 'sometimes' scrolling in the direction opposite to the initial scroll direction gets blocked. Say, I was scrolling with finger pan from left to right, and forced it to some offset, then I can't scroll from right to left anymore.
But the catch is, if I make any tap on the screen, the scrolling starts happening. I am unable to pan, but if I tap the screen, or tap any button, scrolling starts working. If I try to call the button press method programatically after, say 5 seconds of forcing the offset, then it doesn't work. It seems that I need to touch the screen somehow..
I checked the values of contentOffset, contentSize, they seem fine.
PS: there are times when scrollViewDidEndScrollingAnimation: method is not called after forcing the offset, but that is not necessarily the issue.
Edit: Actually, this thing happens when I take the scroll view beyond the threshold offset using my fingers, and keep panning left. At the threshold point, panning stops, but the next time I try to scroll, it doesn't pan. (i.e., I don't give a jerk to go beyond the threshold).
Edit: One more possible loophole: I make scrollEnabled equal to NO just before forcing the new offfset, and just after giving the command to set the new offset, I set it back to YES. I needs to be done so that if I try to scroll the scrollview with a jerk, it doesn't scroll away to the left while trying to set the new offset, since paging is enabled.
Edit: Could it be because I set scrollEnabled to NO while actually scrolling using touch? I do enable it later, but maybe that is some issue...
Important Edit: If I long press on the scrollView, and then try to move, scroll view starts scrolling!
Edit: This code is in scrollViewDidScroll:
if ((theScrollView.contentOffset.x < theScrollView.frame.size.width)
&& [currentlyDisplayedVC isEqual:VC1])
{
//if this is not done, and this call happens when VC3
//is visible a bit too much, scrollView scrolls till VC3.
scrollView.scrollEnabled = NO;
[scrollView setContentOffset:CGPointMake(scrollView.frame.size.width, 0) animated:YES];
scrollView.scrollEnabled = YES;
//this is done so that this block is not reached everytime during scroll animation.
currentlyDisplayedVC = VC2;
}
Then in scrollViewDidEndWithANimation: I add [self VC2reached]
Have you tried using setUserInteractionEnabled:NO and YES to stop/allowing user to interact with the UIScrollView instead of using the scrollEnabled property?
I subclassed UIScrollView and overrode the method touchesShouldBegin:withEvent:inContentView:. In the method I return NO for that particular moment when I see the view stuck, so that all touches are taken in by the scroll view instead of passing them to any other contentView. That solved the problem.
Edit: That doesn't solve the problem actually. I want to disallow touches on contentView ONLY when an attempt to scroll the scrollview is being made, not when some other event like tap on the contentView is attempted. But in ths olution that I posted, all touches will be kept with the scroll view. Do we have a similar touchMoved: method?
Instead of using setContentOffset:animated:
you should try using scrollRectToVisible:animated:
I'm trying to create some sort of timeline view like in video editors: media elements in a row, which are UIView's. I can successfully drag these views inside currently visible part of scroll view using UIScrollView touch events like touchesBegan and touchesMoved. I want to scroll the scroll view once subview is dragged to one of the scroll view edges. The best I can think of now is to create a timer that will scroll the view while user holds the subview with the finger near scroll view edge.
There's a lot of questions here on the same topic, but I was unable to find one that covers scrolling.
Is there a good way to do this? Should I use gesture recognizers instead?
Thank you in advance.
Actually what you want IS a timed event. As soon, as the user is at the edge of the scrollview, you start a timer, which regularly increases the contentOffset. If you don't like your animation results (i guess you're using setContentOffset:animated:?), just try another timing and distance of animation.. I guess you have to try some different settings. What I would try first is 1px at a time. Perhaps every 0.3 second?
If that doesn't work you could also try another "extreme". Start a single animation, when the user reaches the edge, which animates the contentOffset until the end of the contentSize. But over a large timespan so the movement is slow. If the user stops dragging, or moves out of the edge, stop the animation at the current position. That would even be a solution without a timer, because the animation would be your timer itself.
I seriously doubt gesture recognizers would part of a good solution to this since they tend to be most helpful with discreet gestures.
I don't think I can improve on your general direction based on the assumption, implied above, that you are looking for continuous/gradual scrolling.
What I suggest instead is that you consider designing this to use a paged scrolling approach. When your user drags the object to the edge of the scrollview, cause the scrollview to move one page in that direction (by setting the contentOffset to move in that direction according to the bounds of the scrollview). When that even occurs, move the object slightly out of the "hot zone" at the edge of the scrollview so that the user is forced to explicitly express that they want to move another page, or something along those lines - that is, since the design approach depends on this "paging events" you need to implement some sort of gestural system for the user to keep paging.
I suppose you could use a timer in that same situation, so that if the user maintains the position and touch for another second, you would page again.
I have noticed a slight delay on the highlighted state of a UIButton when touched down if it is inside a UIScrollView (or a table view). Otherwise, the highlighted state is pretty much instantaneous.
I surmise this must be by-design to provide a chance for user to scroll. But it just seems like the button is unresponsive to me. Is there a way to fix this?
Indeed, it's a design choice. It needs this small time to differentiate a scroll (panGesture) from a tap. If you eliminate this delay, then the user won't be able to scroll if he places the finger on top of the button, which is not good user experience.
Because a scroll view has no scroll bars, it must know whether a touch signals an intent to scroll versus an intent to track a subview in the content. To make this determination, it temporarily intercepts a touch-down event by starting a timer and, before the timer fires, seeing if the touching finger makes any movement. If the timer fires without a significant change in position, the scroll view sends tracking events to the touched subview of the content view.
from the UIScrollView Documentation
I wouldn't recommend disabling the delay, but if you insist, you can set it in interface builder (select the Scroll View, and on the right panel, right under "Bounces Zoom"), or using this code:
scrollView.delaysContentTouches = false