I have a UICollectionView I use like a tool selection container. You have many tools (the cells), when you select one, the former selected is deselected, and so on... You can only have one tool selected at a time.
The problem is that I can't manage to have the cells selected. When I tap the cell, the collectionView:didSelectItemAtIndexPath: is called. I then reload the selected cell to change it's appearance (I change the alpha of the image) by using the [collectionView reloadItemsAtIndexPaths:#[indexPath]].
Well that reloads the cell ok, except one damn thing: in the collectionView:cellForItemAtIndexPath: the cell never get the selected property set to YES! So I can never change the alphabecause I never know when I must draw a selected cell or not.
Worse: [collectionView indexPathsForSelectedItems] is always empty!!!
I don't even mention the collectionView:didDeselectItemAtIndexPath: that is never called...
Well, if someone can help me understand what is going on, thanks in advance...
When you call reloadItemsAtIndexPaths: the collection view discards those cells and creates new ones, therefor discarding the selected state of the cells.
I'd suggest a couple of different options:
1.) In collectionView:didSelectItemAtIndexPath: call cellForItemAtIndexPath: to get a reference to the selected cell and update it's appearance there.
2.) (My Favorite) Use a custom subclass of UICollectionViewCell if you're not already, and override the method setSelected:. There you'll be notified when the cell is selected and you can update the appearance from within the subclass.
With regards to selecting multiple cell at once, you should try the allowsMultipleSelection property [myCollectionView setAllowsMultipleSelection:YES] The docs for that are here: https://developer.apple.com/library/ios/documentation/uikit/reference/UICollectionView_class/Reference/Reference.html#//apple_ref/occ/instp/UICollectionView/allowsMultipleSelection
Otherwise, #daltonclaybrook's answer is sufficient.
Related
I have a table view with custom cells that have custom highlight styles defined in delegate-functions didHighlightRowAt and didUnhighlightRowAt (e.g., I'm changing the background color).
However, when I select a cell, the unhighlighting function is triggered immediately - how can I avoid this? I want the cell to remain highlighted and instead, unhighlight it in viewwillappear.
Thanks!
[I set tableView.selectionStyle to .none, because it was the only way to do custom highlighting without using the standard selection style. might this be the problem?]
OK, I've fixed this problem, however I think my solution is more like a work-around so better approaches are still highly appreciated!
It looks like the flow is the following:
- releasing a cell
- cell is unhighlighting
- cell becomes selected
So what I did was after unhighlighting, manually highlighting the cell again and then, in in viewWillAppear
I have a custom UITableViewCell that dequeueReusableCells. I have an int called selectedRow which gets the selected rows number in the method of didSelectRowAtIndexPath. I then pass selectedRow to an int called rowNumber which is in the class of my customCell.
In customCell.m, I have the method prepareForReuse. In that I made an NSLog of rowNumber.
What I want to do is: if a row is selected and that row went off screen, then perform some code. I would probably have to use prepareForReuse, but I don't know what to do in it.
I know it's a bit complicated, but if you have any questions, then I'd be happy to answer
Actually, you don't need to call prepareForReuse directly as it would be called automatically:
this method is invoked just before the object is returned from the
UITableView method dequeueReusableCellWithIdentifier:.
and as you don't know what to do in it, note:
For performance reasons, you should only reset attributes of the cell
that are not related to content, for example, alpha, editing, and
selection state
UITableViewCell Class Reference
You can use - (void)tableView:tableView didEndDisplayingCell:cell forRowAtIndexPath:indexPath; in UITableViewDelegate to know which cell is scrolled off screen.
However, this method is iOS6+ only.
You're over complicating things. You don't have to do prepareForReuse the in the custom cell.
Take a look at this.
http://www.icodeblog.com/2009/05/24/custom-uitableviewcell-using-interface-builder/
Its pretty similar for storyboards.
I have a UItableView with custom cell. There are multiple sections, and in those sections multiple rows. In each cell, I have a segment button for "Yes" and "No" selections. I would like to maintain the selections for the segment button when I scroll up and down the table. Can anyone please help. I have looked and did not find anything that helped me. Thank you!
You have multiple ways to do this.
The first one, which I think is the best one, is to use the selected state for the uitableviewcell.
With this method, the table view it self will set the cell's state and according to that state will call didselect or diddeselect on its delegate. Since all is managed by the table view, you don't need additional logic on your cellForRow method, and don't even need to worry about cell reuse.
Another way is to always set the state of your cell's buttons in cellForRow. For this, you need to keep a reference to all the selected rows, and to be able to manage reused cells, you need to make sure its state is always set on cellForRow.
I prefer the first one, but whatever suits you better.
I'm developing an app that represents a huge amount of data using UITableView with a custom UITableViewCell.
When the tableView is set to editing mode, it supports multiple selection for further usage of the selected set of data.
Using -tableView:didSelectRowAtIndexPath: and didDeselect I'm changing the rows UIImageViews image to a little tick and storing the selection into an array. When selecting a cell it gets light blue background (iOS standard).
When I'm now scrolling down and up again, the cells background is still light blue but the image is reset to default and the cells isSelected property is NO. Selecting it again invokes the -tableView:didSelectRowAtIndexPath: method.
After a while debugging it turned out that the reusable identifier was wrong. But as I corrected it, scrolling down repeated the same 12 cells over and over again. And the isSelected property is still reset to NO.
How can I maintain selected rows while scrolling the tableView?! And: Why is the cell blue highlighted (or marked as selected) but the isSelected property gets reset to No?
Thanks for help, with kind regards, Julian
Don't use the cell to hold persistent controller state. Instead keep an NSArray and add the NSIndexPath of each selected cell to your array (and remove them if/when the user deselects a cell).
Then in cellForRowAtIndexPath: just make sure you configure the cell correctly based upon whether or not its index-path is in your array of selected cells.
I use UITableView with static cells.
If I use reloadData, than everything is OK.
If I try reloadRowsAtIndexPaths it hides row. Row appears if I drag tableView up-down(when cell is updated).
If your table cells are static (i.e., you are using the same cell object to replace the one that's currently displayed), what you're seeing is an artifact of the transition animation.
Think of it this way. Lets say you set UITableViewAnimationOptionFade. When the cell is to be replaced, the cell it's to be replaced with (which in this case is the exact same object) has a fade-in animation added to it. Then, the cell that is being replaced (again, it's all the same object) has a fade-out animation added to it. At the end, the cell is actually there, but it's invisible because the fade-out animation has made that cell object invisible.
In a non-static tableview, one in which the replacement cell is a different object than the cell to be replaced, this isn't a problem, as the animations are added to two different objects.
I had the same problem, it seems to be a bug. I experimented some and the problem doesn't occur when I set the animation option to UITableViewRowAnimationNone. Some other interesting stuff happens when you set that option to UITableViewRowAnimationTop, too.
I solved this by removing animation
tableView.reloadRows(at: [yourIndexPath], with: UITableView.RowAnimation.none)
Hope this helps to anyone searching for this.