I have an unusual and challenging problem. I have researched deeply on StackOverflow and have been unable to find any solutions. Please do not ask about my design style- it must be this way.
I have a UIPageViewController that contains a UIScrollView which contains 4 UICollectionViews. Each of these collection views should be horizontally scrollable but not vertically scrollable. The scroll view is necessary because the screen is not large enough to display all 4 collection views. Upon loading the screen, the 4th collection view is not immediately visible. After scrolling down, the 4th collection view then becomes visible.
The problem I am having is the 4th collection view does not respond to touches. Specifically, it does not respond to taps or attempts to scroll. The other 3 work perfectly fine. What makes this puzzling and odd is that the 4th one is exactly the same as the other 3, the delegate and data source are set properly and user interaction is enabled. The only real difference between the problematic collection view and the others is that it is not immediately visible when the screen loads.
When I attempt to scroll it behaves as if I am trying to change the page, so the UIPageView changes the page. So the CollectionView isn't registering any touches at all. I have a hunch that it either has to do with the GestureRecognizer from the PageView or something to do with how it isn't visible on the screen upon the initial load.
Any thoughts?
Not 100% sure without seeing the initialization of code or storyboard, but the best thing is that maybe there is a view overlapping. You can run your program and click on the 2 overlapping rectangles. This is the Debug View Hierarchy. It shows you your current frame on your phone and you can see the view laid out in hierarchal status.
Solved my own problem thanks to impression7vx's mention of the Debug View Hierarchy. Had no clue this existed but it let me discover the flaw. I am just writing this to help people who stumble upon this in the future.
I had a content view inside the ScrollView that had a problematic constraint. I set it to have "Equal Heights" with the ScrollView but upon loading the screen the height was static. Only half of the scroll view showed and that half would be registered as the height for the UIView. Since it was static the view would not become larger when I'd scroll, and the 4th collection view would not be inside that container view anymore. For some reason, since the collection view wasn't in the container view it wouldn't register touches.
Solved by manually making the height the same value of the scroll view! This allowed the content view to contain all of the collection views which made them behave normally again.
Just take NSLayoutConstraint of height of the UIView inside the UIScrollView
#IBOutlet weak var scrollContentViewHeight: NSLayoutConstraint!
Set height of this scrollContentViewHeight equal to height of dynamic size of the UIScrollView
if scrollableView.contentSize.height = 840.0
then
scrollContentViewHeight.constant = 840.0
set it on viewDidLayoutSubviews
override func viewDidLayoutSubviews() {
scrollableView.contentSize.height = 840.0
scrollContentViewHeight.constant = 840.0
}
Related
I have a scroll view which works fine. Almost. I'm building in Any/Any. The problem is that the scroll view won't scroll past the view controller. I have a switch that is mostly in the view controller window, but the rest is off the box (not really sure how to describe it; it's in the view in the scroll view, but the view is longer than the view controller so part of it is hidden).
The scroll view will scroll down until it hits the part where the view controller would end if you were looking at it in Xcode. There is some more stuff under the switch (labels and another switch). To view these you have to forcefully scroll down. Xcode shows no constraint errors (little red circle with white arrow).
Hopefully this makes sense
A ScrollView needs to know the height and width of the content it is holding in order to know how much to scroll and which direction. Here is a quick read on how ScrollViews work in iOS: https://www.objc.io/issues/3-views/scroll-view/
You can set this programmatically using the contentSize property, but this requires you to know and or calculate the contentSize, which is pretty tedious in most cases.
The correct way of defining the contentSize in iOS is to define AutoLayout constraints in your View. Here is an excellent tutorial on doing just that:
https://www.natashatherobot.com/ios-autolayout-scrollview/
I've been trying to replicate this effect for a couple days which was inspired by Tumblr.
I've previously asked questions on here with different approaches of the same problem but to no avail. I'm just curious as to how the engineers at Tumblr created a horizontal collection view, with two vertical collection views, and is able to scroll down without affecting the view above (without resetting the position of the view when you scroll vertically in a different tab).
Header Views
I tried this, but the header view was isolated and I had to scroll to the right to see the collectionView cells. This did not work.
Changing the topLayoutConstraint constant of my UIView (not cv header) with respect to the contentOffSet of the vertical collectionView.
This almost got the effect I wanted, except that when I scrolled horizontally, there was a huge gap between my collection view and if I scrolled in that new tab, the UIView would appear again because, again, topLayoutConstraint gets scrolled up depending on the contentOffSet of my vertical collectionView contentOffset.
Changing the position of the UICollectionView frame, and scrolling the super view up simultaneously with NSNotificationCenter.
Alas, this method did the same as method #2, except that the vertical collection view cells scrolled faster than the super view.
I ran out of options to make this work so I will show you in detail what's attempted to be replicated (also note the scroll bar on the right):
Note when I scroll down the first tab. I switch, and then scroll down further. Originally, as I've said, there would be a gap between the second main CV, and when I scrolled, the view would reposition as if were scrolling up again. On here, the view on top keeps going up. So I'm curious as to what method Tumblr engineers used to do this. UICollectionView inside UIScrollView? Other suggestions?
I believe there is no UICollectionView involved. It looks like UIPageViewController and each its page is a UITableView.
Perhaps the UIPageViewController sits in a UITableView as well - the header also moves up when you scroll. This main table has only one cell (and a header) which is occupied by the UIPageViewController.
Hope it helps.
I have the following layout
So it's basically a scroll view that occupies whole screen. Content size is set to triple-width and same height. Inside the scroll view - there is container view and three table views - one per page. Only middle table view is visible initially.
This allows me to use scroll view horizontal scrolling to navigate between the tables and vertical scrolling inside the middle table.
I know that Apple doesn't really recommend putting UITableView inside UIScrollView, but in this particular case I don't know how to implement it differently, and until iOS8 everything was working fine.
UIScrollView would not recognize any vertical scrolling (since content height was equal to scroll view height) and these gestures were passed directly to UITableView.
But starting in iOS8 - this getting broken. UIScrollView would allow some vertical scrolling and basically intercept scrolling gestures sent to UITableView.
I created a simple project that works fine in iOS7 but is broken in iOS8. Anybody has any idea how to fix this problem?
Link to the project: https://dl.dropboxusercontent.com/u/6402890/TablePaging.zip
I haven't been able to solve this and as I mentioned in comments had to re-write logic using built-in UIPageViewController class.
If I change the Class of your ScrollView in Interface Builder to UIScrollView, it fixes part of the problem. Now just the UITableView goes up and down, and I go left-and-right, but haven't gotten rid of the space at the top.
I have a .xib containing a view which itself containing top and bottom accessory views (navigation, a page control) and a UIScrollView. Its height varies depending on whether I'm running on an iPhone 4 or 5 (3.5" or 4"). At runtime I move the containing view offscreen, populate the scrollview with UIButtons to build a scrollable launchpad, and scroll this on to the screen from the bottom. Tapping a button shows another view.
On a smaller screen I'd like to show only three buttons in the scrollview, on the larger one I show four. So I need to know the height that the scrollview will be when it appears, before it actually appears. I'd hoped to have this information available at some point in the view lifecycle (viewWillAppear etc.) but the only place this seems to be correct is in viewDidAppear. At this point the view is already on screen and creating the buttons then means they appear suddenly, and are not scrolled nicely onscreen.
The top-level view in the .xib is set to Retina 4 FullScreen.
I'm happy to concede that viewWillAppear is the correct place to create the buttons and my navigation controller is perhaps instantiating the view incorrectly, but my iOS-fu isn't strong enough to say for certain.
My solution has been to detect screen size and hardwire the button height. Is there a better (more elegant, future-proof and canonical) way to do this?
Don't worry, you are in the right direction:
viewWillAppear is the correct method in a view's lifecycle, where the frames of that view and its subviews are completely calculated and nothing has been drawn yet. Here you can make corrections to the standard behavior of your view.
When viewDidAppear gets called, you get the same information about positions and sizes of view elements as in viewWillAppear. But at this time, the animations and the view itself already have been drawn.
That is, why you'll want to use viewWillApear.
I've created a UITableVIew and it is a subview of a UIView. There are three issues that i'm having and it is only occurring on iOS 4 devices:
1) The table doesn't bounce when the view hits either the top or bottom of the table while scrolling. The vertical bar doesn't shrink either, it feels sticky and it is very much acting like an Android table view. I've tried enabling the bounce property but that doesn't make any difference.
2) The horizontal scroll bar appears when the view is scrolled down to the bottom of the table. This shouldn't appear since the table view's contentSize has been set correctly. It does eventually disappear when the contentSize is set 20 pixels less than what it should be.
3) I can't scroll to the bottom of the footer view, and only half the footer view is visible.
I've added a UITableView as a subview to other views throughout my project and this has never occurred, and so i've copied the way that I create other UITableViews, but still no luck.
Any suggestions would be greatly appreciated.
Thanks,
Ankur
I worked out the problem. The problem is a little strange, although i had a feeling that the way i was coding was a little messy.
I am subclassing a View, and the parent view has a layoutSubview method, which is only calculating and setting the frame for a table view subview. In the subclass, i had to override layoutSubview for the same reason as the values for the table view's frame need to be different. This means that the table view's frame was being laid out twice, once by the parent class and a second time by the subclass. It seems that iOS 4 doesn't like this, and i should only set the frame once per subview per layoutSubview call.
Now i've created a layoutTableView method, which is called from the parents layoutSubview, and i've overridden layoutTableView in the subclass. Therefore the table view's frame is only being set once.