ios - UICollectionViewCell resizing on device rotation -

i have simple uicollectionview embedded in viewcontroller.

the uicollectionview uses auto-layout (defined in ib) take whole space in viewcontroller.

my uicollectionviewcell have same size , take whole space of uicollectionview because want 1 cell displayed in viewcontroller. uicollectionviewcell displays uiimage (which embedded in uiscrollview zooming).

it works fine except when device rotate. there's error message:

the behavior of uicollectionviewflowlayout not defined because: item height must less height of uicollectionview minus section insets top , bottom values, minus content insets top , bottom values. relevant uicollectionviewflowlayout instance , , attached ; animations = { bounds.origin=; bounds.size=; position=; }; layer = ; contentoffset: {0, 0}; contentsize: {4875, 323}> collection view layout: .

that's pretty clear, need resize uicollectionviewcell fit new height / width. after rotation uicollectionviewcell display appropriate height / width poor animation.

here's code:

@iboutlet weak var thecollectionview: uicollectionview! @iboutlet weak var theflowlayout: uicollectionviewflowlayout!     override func viewdidload() {     super.viewdidload()      //thecollectionview.delegate = self     thecollectionview.datasource = self     automaticallyadjustsscrollviewinsets = false     theflowlayout.itemsize = thecollectionview.frame.size     theflowlayout.sectioninset = uiedgeinsetsmake(0,0,0,0)     theflowlayout.minimumlinespacing = 0.0     thecollectionview.reloaddata() }   override func viewwillappear(_ animated: bool) {     super.viewwillappear(animated) }  override func viewwilltransition(to size: cgsize, coordinator: uiviewcontrollertransitioncoordinator) {     super.viewwilltransition(to: size, with: coordinator)     print("\(#function) \(view.frame.size)")     coordinator.animate(alongsidetransition: nil, completion: {         _ in         self.theflowlayout.itemsize = self.thecollectionview.frame.size     })         }  override func viewwilllayoutsubviews() {     super.viewwilllayoutsubviews()     print("\(#function) \(view.frame.size)") }  override func viewdidlayoutsubviews() {     super.viewdidlayoutsubviews()     print("\(#function) \(view.frame.size)") } 

the question is, how , when perform uicollectionviewcell change avoid warning , smooth animation?

when device rotation happens, can see following: viewwilltransition(to:with:) (375.0, 667.0) viewwilllayoutsubviews() (667.0, 375.0) viewdidlayoutsubviews() (667.0, 375.0)

the error displayed after viewdidlayoutsubviews(). have tried call theflowlayout.invalidatelayout() in viewdidlayoutsubviews() doesn't change issue.

i have read others similar questions not find answer :-(

thanks help,

sebastien

i have not found best solution @ least works.

i use viewwilltransition compute index of cell , reset offset after rotation. avoid poor animation set alpha 0 , @ beginning , 1 again @ end of animation.

viewwilllayoutsubviews used invalidated layout of uicollectionviewflowlayout , viewdidlayoutsubviews set new cell size.

maybe others if have better solution, please share it!

    @iboutlet weak var thecollectionview: uicollectionview! {     didset {         thecollectionview.backgroundcolor = uicolor.black         thecollectionview.delegate = self         thecollectionview.datasource = self     } }  @iboutlet weak var theflowlayout: uicollectionviewflowlayout! {     didset {         theflowlayout.itemsize = thecollectionview.frame.size         theflowlayout.sectioninset = uiedgeinsetsmake(0,0,0,0)         theflowlayout.minimumlinespacing = 0.0     } }  var assets:[phasset]! var startassetindex = 0  override func viewdidload() {     super.viewdidload()     view.backgroundcolor = uicolor.black     automaticallyadjustsscrollviewinsets = false     thecollectionview.reloaddata() }   override func viewwillappear(_ animated: bool) {     super.viewwillappear(animated)     thecollectionview.scrolltoitem(at: indexpath(row:startassetindex, section:0), at: .left, animated: true) }   /// resize collectionview during device rotation /// /// - parameters: ///   - size: new size of viewcontroller ///   - coordinator: coordinator animation override func viewwilltransition(to size: cgsize, coordinator: uiviewcontrollertransitioncoordinator) {     super.viewwilltransition(to: size, with: coordinator)      // compute index of image/video displayed     let offset = self.thecollectionview.contentoffset;     let index = round(offset.x / self.thecollectionview.bounds.size.width);      // hide collection view avoid horrible animation during rotation     // animation horrible due offset change     thecollectionview.alpha = 0.0     coordinator.animate(alongsidetransition: nil, completion: {         _ in         // display collectionview during animation         self.thecollectionview.alpha = 1.0          // compute new offset based on index , new size         let newoffset = cgpoint(x: index * self.thecollectionview.frame.size.width, y: offset.y)         self.thecollectionview.setcontentoffset(newoffset, animated: false)     }) }   /// invalidate layout of flowlayout, it's mandatory rotation override func viewwilllayoutsubviews() {     theflowlayout.invalidatelayout()     super.viewwilllayoutsubviews() }   /// set size of items (mandatory rotation) override func viewdidlayoutsubviews() {     super.viewdidlayoutsubviews()     theflowlayout.itemsize = thecollectionview.frame.size }