I have a UICollectionView that has a custom layout that changes the sizes of its cells when the device rotates. When the layout changes the size of a cell, layoutSubviews is called on each cell. This is what I want. However layoutSubviews does not execute in an animated manner but the change in size of the cell does. I would like to synchronize the two changes.
For example right now if the cell gets larger, the subviews resize instantly and then the cell size animates its change. I don't think I should put animation code in layoutSubviews. Is that correct? What is the best way to handle this?
Related
I'm trying to resize a UILabel frame in a custom UICollectionViewCell. I added the label to the cell in Storyboards. The frame gets adjusted in -layoutSubviews. The frame is getting resized when layoutSubviews is called, but it isn't displaying the resize when the cell is displayed.
Here's what I'm assuming based on what I've seen...
It seems as though calling -layoutSubviews forces a re-layout on
every cell in the CollectionView, which hurts performance.
With auto-layout on, you simply can't resize the label.
If I delete the label in Storyboards, create the it
programmatically, and set the frame when the cell is called in
-cellForRowAtIndexPath, it works like a charm.
Are my assumptions above correct, and if so, is there an alternate to -layoutSubviews better suited for CollectionViews.
I have a UITableView that has multiple sections, with custom UITableViewCell subclasses populating the table. Within these UITableViewCell subclasses, I am implementing layoutSubviews to customize the position of labels, etc.
All of the cell's subviews are adjusting as they should, except the first batch of visible cells upon the view loading. They are identical to how they are laid out in storyboard, which is not what I want. For example:
http://i.stack.imgur.com/L5GJh.png
Note: The green and orange borders are a visual aid to see if the labels are resizing.
Upon scrolling, all of the new cells that appear have their subviews the way that I programmed them to be in layoutSubviews. As far as the first batch of visible cells, I can scroll them offscreen and then back on, and then the subviews are laid out perfectly. For example:
http://i.stack.imgur.com/jgjch.png
Within tableView: cellForRowAtIndexPath:, I call [cell layoutIfNeeded] before the method returns the cell. If I change this to [cell layoutSubviews], then the inverse happens, where the first batch of visible cells are laid out as they should be, but all of the cells that get loaded upon scrolling are not laid out properly.
I have tried to put [cell layoutIfNeeded] within [tableview: willDisplayCell: with no luck. Any ideas on how to fix this?
Thanks in advance!
This is the behavior you'd see if you were setting frames in your layout code with Auto Layout enabled. This won't work. The Auto Layout system is responsible for setting frames and will overwrite the values you set.
You should either specify your layout using constraints or turn off Auto Layout.
I am trying to have the content in a uicollectionviewcell grow bigger when it scroll moving in one direction. i initially set the size of the cell to the largest size i want, then the content inside the cell is half in terms of the size. the content is an uiimageview.
So I have a custom UICollectionViewFlowLayout in which I subclassed the layoutAttributesForElementsInRect to make the uiimageview in the cells grow bigger when it is moving in one direction. i also have shouldInvalidateLayoutForBoundsChange to return YES
Everything works perfectly when i scroll, the imageview will grow larger. However if i select a cell to push to a new viewcontroller, and then when i click the back button to come back to this uicolletionview, the enlarged uiimageview in severals cells are showing in the original size. They can only go back to the correct enlarged size if i scroll again, why is that? and how can i make it keep its enlarged size after getting pushed?
i tried invalidatelayout but it will just refresh the layoutattributes with correct enlarged size of the content, but the view is just not updated eventhough the size is already enlarged.
thanks
I had a similar issue when designing cv cells and would gess the issue is with when the subviews get calls to update their size, which might not happen when the view refreshes.
Instead of resizing content in the cell, you might want to dynamically size the cells themselves and have the content automatically adjust to that size. Calling [mycollection invalidateLayout] then should be all you need, maybe not even that.
The method is
collectionView:layout:sizeForItemAtIndexPath:
which you declare in your UICollectionViewFlowLayout.h
If you then run into trouble where subviews do not resize with cell size, related problems can arise from constraints/autolayout etc of the subviews.
I have a grouped table view with custom cells (created programmatically by subclassing, not with IB). To properly position custom cell's subviews (such as labels and text fields), I need to know the current width of the cell's contentView just before the cell displays (taking into account that real cell width in a table view can change (according to screen orientation, modal presentation style, etc.)).
if I override in custom cell class the layoutSubviews method, it works perfectly, but it can be called frequently, thus I have to reposition my subviews every time when it's called, even when there's no need to do that.
Please, recommend me more elegant solution.
The recommended way of doing this is by setting the autoresizingMask of the table cell. If you need to have more control over the layout, you can store the last used view width in a member variable, and only layout the subviews if this differs from the current view width.
I always thought that whatever changes I perform in layoutSubViews: is done animated?
Is this incorrect information?
In my case I'm inheriting from a UITableViewCell.
The controller gets informed that the user wants to enlarge the cells, so I first use a UITableView animation block to increase row height. The height increases smoothly animated to the new height.
Then I loop my visible cells, set a flag and call setNeedsLayout:
The cells indeed layout and adust the content to the new height but without animation.
No, that is not correct, the default approach for layoutSubviews will not be performed animated, it is up to you to begin / commit an animation block or use the blocks animation feature.