I'm using performBatchUpdates: to insert a new section to my collection view. This comes with the default fade in animation that I'd like to keep. The item I'm inserting is always the last item, so I'd like to offset my collection view to the bottom to make it visible.
Right now I'm able to achieve this by using scrollRectToVisible: in the completion callback of the batch update method. However, by the time it scrolls, the fade in animation already happened out of frame.
I'd like for both to happen simultaneously. Is this possible?
One approach I've tried is pre-calculating the new size manually ahead of the updates and scrolling first, but then the cells get reused right on screen, appearing and disappearing, which is not ideal.
Any ideas?
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I have an NSCollectionView with a vertical NSCollectionViewFlowLayout. I display rectangular icons in it.
I also have a slider in the UI, and when that changes, I adjust the minItemSize, which I then use in collectionView:itemForRepresentedObjectAtIndexPath: to create an equally sized NSImageView to the returned NSCollectionViewItem's imageView. Then I reload the view by invoking reloadData.
After that, the view shows the icons in the new size as intended.
The problem is, provided I have more data to show than fits into the current scoll view, that when the General System Preferences are set to Show scroll bars: When scrolling, the scrollbar disappears after reloading the collection view, and trying to scroll with the trackpad leads to a bounce that's telling me that the scroll view thinks that the content is just what's visible, nothing more to scroll.
But as soon as I resize the window, which also resizes the collection view inside, the scrollbars come back.
Curiously, if the System Prefs are set to Show scroll bars: Always, then the issue does not appear and the scrolling always works, and the scrollbars always remain visible.
I've tried a lot of things to trigger the re-calculation of the scroll view, such as invalidating the layout of the collection view's layout, the scroll view itself, its content view, and also tried to set their needsLayout to true. Nothing makes this work.
Update: The potential duplicate (NSCollectionView does not scroll items past initial visible rect), neither the collectionView.setFrameSize: nor the window.setFrame: suggestions work for my case (I tried adding these line before and after reloadData).
Even if I force a resize of the window like this, it doesn't bring the scrollbars back, only a manual dragging of the window edges does:
[self.collectionView.window setFrame:NSInsetRect(self.view.window.frame, 1, 1) display:YES];
Also note that in my case, initially the scrolling works, just not after resizing and reloading.
Another finding: When I call selectItemsAtIndexPaths:scrollPosition: after reloadData, then the scrollbar comes back. But only if I pass a non-empty NSSet for the paths. And since I may not have selected any items, this isn't a permanent solution.
If no other ideas come up, I'll try to make a demo project.
I've solved it:
I had to delay the call to reloadData, e.g. by calling it from within the block code of dispatch_async(dispatch_get_main_queue(), ^{ ... });
Before the fix, I did call reloadData right from the setSliderValue: handler, which is bound to the slider's value. It appears that this didn't go well together.
I have a collection view that is 100 points wide with a number of cells that are each also 100 points wide. I've got it setup to support scrolling and paging horizontally so the user can flick left and right and each cell occupies the entire collection view frame.
Originally, I had no scrolling and the user would tap each cell to activate something in the app. Now that its a narrow frame where only one cell can be seen at a time I feel that tapping is redundant and the cell should simply be tapped in effect when it comes in view.
Is there a way to trigger an event such as didSelectItemAtIndexPath when a given UICollectionViewCell becomes the one displayed within my collection view's frame?
UICollectionView responds to selectItemAtIndexPath:animated:scrollPosition:.
It also responds to indexPathsForVisibleItems which will be useful to determine where to make the selection.
You also need to decide when to make the selection, probably best after receiving scrollViewDidEndDecelerating: which the delegate inherits from UIScrollViewDelegate).
But it may be even better advice to look at what your code does upon selection and just do that (launched from the same place in code, probably when scrolling is finished), leaving selection out of it.
Initially I was under the impression that it uses the table row slideup/down animations while inserting/deleting new rows but I doubt if it's doing that as it does it so fluidly even with thousands of items in the list (otherwise it would take a lot of time for the deletions/insertions to work).
Am I right in my assumption that it's simply attaching a new instance of the News list at the bottom of the screen, shrinking the above one while the one at the bottom expands to fill up space?
UPDATE:
Please see this video of what I mean: http://dl.dropbox.com/u/4960327/ReederAnim.mov
I can not tell you exactly how Silvio Rizzi made this, but as you see in the playback, a list view is added behind the shown list view, and the front list view fades out (.alpha = 0.0;) while the list view behind it expands its height per row.
When you desicate it frame by frame it becomes quite clear what he does, and it is really not that advanced. But I have to admit, with the white "milky" polished interface, it looks quite neat.
In addition, you can see that while animating, the background list view only renders the top 7 entries (hopefully calculated by dividing the view height with the average height of the cells shown) making the list view quick to load. Then afterwards, he can load an extended array of cells once you start scrolling, or in a background thread starting once the animation is complete.
After reading this, I'm interested in being able to dynamically update a UITableView without the view scrolling. That is, if the 12th row is visible, and some background process runs and calls for a new row to be inserted at position 0, how can that be done without the table appearing to scroll?
The closest I've been able to come to achieving this is to do any and all updates in a single -beginUpdates/-endUpdates block and to adjust the contentOffset as appropriate after that. But some of my code might have a bunch of calls to -insertRowsAtIndexPaths:withRowAnimation called outside such a block, and when I do that, the thing can scroll all over the place.
How can I make UITableView stand still?
Is there a simple way of animating rows in an NSTableView?
I'd like to be able to do something like flash a row, or fade out a row.
Essentially - to provide a bit of visual feedback when rows are added or removed.
Edited to add:
I'd had a quick look over Google before posting this; but I wanted to know if there was some way to do this that I'd missed other than drawing and animating parts of the table view myself.
To flash a row, there are a number of ways to go. You could just grab a cell and play with it's view, such as change the color of the background or font colors. You could also just select the cell and deselect it a few times, if you don't care about removing the existing selection from another cell. Or you could superimpose another view on top of the cell's view and use blend modes...
For animating the deletion, you could do the same as above, dimming the cell, or even move the view up and out, transform it so it shrinks down and move it over to a trash can and shrink it all the way down as it enters the trash. Then after the animation is done, you delete the row.