I know that it would be repeated question but I really stuck on it. My first CollectionView’s each cell has another collectionView as a subview. My first CollectionView has three cells with same width and height and my Second collectionView has 27 cells. I want to show edge of next and previous cells at second cells of the first collection view and got it using the ScrollViewDidEndDecelerating delegate method of the uiscrollview but the problem is the he gets called even simple touch on any collectionview item. Please help me, how do I get rid of this shit?
If anyone wouldn’t get my point I can share code as well.
Related
I am facing a weird issue, UICollectionView reuses cells even if there are enough space in screen and not scrolled also.
I have only two cells in the iPad screen, still every time with reload data, cells getting reused alternatively like below
First time reload - First and Second Cells appear with address 0x00007ff3f2c1a8b0 and 0x00007ff3f2830040 respectively
on the same screen - Second time reload - cells appear with address 0x00007ff3f2830040 and 0x00007ff3f2c1a8b0 respectively.
Can any one help me understand for this behaviour of collection view.
Thanks in advance.
When you call dequeueReusableCell(withIdentifier:) method, you should always expect it to be reused. You cannot predict the order of the cell dequeue.
If you want to be prepared for it, use prepareForReuse() method.
I have custom UICollectionViewCell in xib. When ViewController is loaded - awakeFromNib() in cell subclass called 6 times (the screen initially placed 6 cells, ok), BUT when i start to scroll, awakeFromNib() is called six times more, causing lag. But after this "re-load" scrolling begins to work smoothly. This happens only the first time at scroll start. dequeueReusableCell, obviously, is used.With UITableView instead collection the situation is similar.
Feel like the next 6 cells are loaded from the xib again (in the collection of just 100+ cells), ignoring reuse. What could be the problem?
For clarity:
UIColectionView with Vertical scroll direction, two cells in line. When ViewController loaded i see 6 cells on screen and 6 awakeFromNib calls in console.
I start scroll down to 7-8 cells, before their appearance on the screen i see lag and 2 calls of awakeFromNib method.
Similarly for the following two pairs of cells.
After this scroll begins work fine, until cells 99-100+, and awakeFromNib is never invoked.
Added:
OK, here's what I found out:
I have a subView inside a collectionView (header like in UITableView), and, accordingly, collectionViewLayout set sectionInsets top = height of header. If I remove the header, and make the top insets, for example: -180 (about excluding the height of NavigationBar, so the screen initially fit 12 cells and the scroll lag is gone.
Ie, the system needs to load from the xib at all the cells that will be one-time visible on the screen and reuse them in future. (But why not one time load xib and reuse it immediately for all other initially cells?)
And now the question - how to fix it?
Added.2
Working solution - add header in viewDidAppear method of ViewController, but this... hm.. not good.
This is actually a known side effect (or purposeful design?) of UICollectionView & UITableView. Here's a related question (talking about NSTableView, but the concepts/issues are the same):
awakeFromNib method called multiple times
Your collection view initially displays six cells to start with, but it sounds like iOS is allocating six more cells to allow for scrolling left & right. So there are at least 12 (reuseable) cells in memory.
If you're doing a lot of work in awakeFromNib (which is what's contributing to the lag), you might want to try to determine how to optimize things.
You can also find some additional helpful hints in this related question:
UITableViewCell - Best place to set up the cell
So, my problem is pretty simple. I have a UITableView in a UIViewController. The tableview has dynamic cells (custom cells with images , text, etc.. from a subclass I created) and these cells belong to a subclass I created. Everything is going fine since the content is different on each cell. The problem is that when I scroll the scrollview of the cell which is horizontal ( I have a UIScrollView in the subview of the cell. I created this scrollview on the cell subclass), on let's say, indexPath.row == 0, and scroll the tableview vertically, after about 8 cells, the ninth cell has the scrollview scrolled as well. This is because of dequeuereusablecells, so the ninth cell is actually the first one, only displaying different content but since it is the first cell, it has the same background operation (the scrollview scrolled).
I tried to unscroll in the cellForRowAtIndexPath: but although this solves the problem it creates another : The first cell that was scrolled is not anymore. So, to solve this new problem I am planning on adding a workaround here that is a dictionary of [Int:Bool], that is, the indexPath corresponding to a Boolean value. If I scrolled the first cell, then 0:true. If I reach the ninth cell (which is equal to the first cell, but with IndexPath = 8 ), I unscroll the cell's horizontal scrollview. If I come back to the beginning of the tableview and reach the first cell, I scroll the cell's horizontal scrollview back. What do you guys think?
The other workaround I can think of is just not use dequeue reusable cells since I don't think I will have more than 30-50 rows on my tableview.
In terms of performance, which operation is better?
Firstly, I would suggest you to carefully analyse whether removing scrolling offset from the first cell is such a bad idea. If I am a user and I scroll down to the very bottom, making the first cell invisible, are you sure that I want it to return to the scrolled position after I scroll back to top? The answer might be Yes, but you should think about this carefully because it might lead you to the simplest solution.
However, in case you really need to do it, I would have a variable which stores the state of the scrolling for each row. If you have an array of objects from which you pull necessary properties (title, image etc) you can add this as an extra property to these objects. Otherwise, you can create an array which will be storing this info (I would prefer an array over dictionary for this task).
Fundamentally it's an issue caused by table view cell reusability. You can have workarounds, but I'd say that, things that aren't supposed to be reused should not be reused.
If your cells are all similar (with minor differences), you could use just one cell identifier; If you have very different types of cells, say, one type has a horizontal scroll view inside, one type just has some labels and images, you might want to consider to have two identifiers, so cells that have UIScrollView won't be reused for normal cells.
And at the same time, you can still do necessary cleanup works in prepareForReuse: to make sure cells that just get dequeued have a fresh start.
I have tried looking for an answer to this question but so far I haven't got any luck.
Context
I have a UITableView inside a standard UIViewController (NOT a UITableViewController..). I have subclassed UITableViewCell and all the cells in the tableview are from the same class.
Requirement
I would like to find an efficient way to resize the cells based on the scrolling of the tableview. For example, when the cell is at the bottom of the visible list, the height is X. When the cell moves up on the screen, its height should proportionally increase to 2X.
Additional Info
I am close to just ditch the UITableView way and start making my own control that would implement such a feat by subclassing a UIScrollView. However, I would like to see if it is possible before going this path. I did see some very interesting SO posts but nothing that would put me on the right path.
Any hint or help would be highly appreciated.
You would need to respond to the scroll view delegate method scrollViewDidScroll: and implement it to record the cell at the top of the table view and reload the table view. Then your table view delegate method tableView:heightForRowAtIndexPath: sets the cell height by the relationship between the index path and the top cell index path.
Your main issue is performance while reloading the table view all the time.
If you wanted to roll your own solution it would be along the lines of the above description anyway, but you would be able to be more efficient than the table view as the table view will call the tableView:heightForRowAtIndexPath: method once for every row for every reload in order to calculate the total height of the table content.
I'm puzzled with this.
I have a UIScrollView and inside I have placed 4 tableViews.
The whole thing is used to allow scrolling horizontally and switching tableViews like the Groupon app.
As soon as you start scrolling the 4th (left or right) tableView, is moved in the scrollView and a reloadData is initiated on that tableView, so it will load the data from the datasource for that category.
However, when I scroll into that tableView, it still has the data from the previous category, meaning the cell's didn't get refreshed.
Can anyone shed a light on why this is happening?
I'm guessing only that because the tableView is not in a visible frame when I call the reloadData command, actual drawing is not happening in the tableView (the datasource methods are being called normally, but no drawing is happening).
Any ideas, or tips ?