问题
I used UICollectionView (flowlayout) to build a simple layout.
the width for each cell is set to the width of screen using self.view.frame.width
but when I rotate the device, the cells don't get updated.
I have found a function, which is called upon orientation change :
override func willRotateToInterfaceOrientation(toInterfaceOrientation:
UIInterfaceOrientation, duration: NSTimeInterval) {
//code
}
but I am unable to find a way to update the UICollectionView layout
The main code is here:
class ViewController: UIViewController , UICollectionViewDelegate , UICollectionViewDataSource , UICollectionViewDelegateFlowLayout{
@IBOutlet weak var myCollection: UICollectionView!
var numOfItemsInSecOne: Int!
override func viewDidLoad() {
super.viewDidLoad()
numOfItemsInSecOne = 8
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func willRotateToInterfaceOrientation(toInterfaceOrientation: UIInterfaceOrientation, duration: NSTimeInterval) {
//print("orientation Changed")
}
func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return numOfItemsInSecOne
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cellO", forIndexPath: indexPath)
return cell
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize{
let itemSize = CGSize(width: self.view.frame.width, height: 100)
return itemSize
}}
回答1:
Add this function:
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
myCollection.collectionViewLayout.invalidateLayout()
}
When you change the orientation, this function would be called.
回答2:
The better option is to call invalidateLayout() instead of reloadData() because it will not force recreation of the cells, so performance will be slightly better:
override func viewWillLayoutSubviews() {
super.viewWillLayoutSubviews()
myCollection.collectionViewLayout.invalidateLayout()
}
回答3:
Also you can invalidate it in this way.
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
[super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
[self.collectionView.collectionViewLayout invalidateLayout];
}
回答4:
The viewWillLayoutSubviews() did not work for me. Neither did viewDidLayoutSubviews(). Both made the app go into an infinite loop which I checked using a print command.
One of the ways that do work is
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
// Reload here
}
回答5:
to update UICollectionViewLayout traitCollectionDidChange method might be used as well:
override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
super.traitCollectionDidChange(previousTraitCollection)
guard let previousTraitCollection = previousTraitCollections else {
return
}
collectionView?.collectionViewLayout.invalidateLayout()
}
回答6:
you can update your UICollectionView Layout by using
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
if isLandscape {
return CGSizeMake(yourLandscapeWidth, yourLandscapeHeight)
}
else {
return CGSizeMake(yourNonLandscapeWidth, yourNonLandscapeHeight)
}
}
回答7:
When UICollectionLayout detects a bounds change, it asks if it needs to reroute the Invalidate layout. You can rewrite the method directly.UICollectionLayout can call invalidateLayout method at the right time
class CollectionViewFlowLayout: UICollectionViewFlowLayout{
/// The default implementation of this method returns false.
/// Subclasses can override it and return an appropriate value
/// based on whether changes in the bounds of the collection
/// view require changes to the layout of cells and supplementary views.
/// If the bounds of the collection view change and this method returns true,
/// the collection view invalidates the layout by calling the invalidateLayout(with:) method.
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return (self.collectionView?.bounds ?? newBounds) == newBounds
}
}
回答8:
I was also having some problem but then it got solved using :
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
collectionViewFlowLayoutSetup(with: view.bounds.size.width)
collectionView?.collectionViewLayout.invalidateLayout()
collectionViewFlowLayoutSetup(with: size.width)
}
fileprivate func collectionViewFlowLayoutSetup(with Width: CGFloat){
if let flowLayout = collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.estimatedItemSize = CGSize(width: Width, height: 300)
}
}
回答9:
I solve this by setting notification when screen orientation changes and reloading cell which set itemsize according to screen orientation and setting indexpath to previous cell. This does work with flowlayout too. Here is the code i wrote:
var cellWidthInLandscape: CGFloat = 0 {
didSet {
self.collectionView.reloadData()
}
}
var lastIndex: Int = 0
override func viewDidLoad() {
super.viewDidLoad()
collectionView.dataSource = self
collectionView.delegate = self
NotificationCenter.default.addObserver(self, selector: #selector(rotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
cellWidthInLandscape = UIScreen.main.bounds.size.width
}
deinit {
NotificationCenter.default.removeObserver(self)
}
@objc func rotated() {
// Setting new width on screen orientation change
cellWidthInLandscape = UIScreen.main.bounds.size.width
// Setting collectionView to previous indexpath
collectionView.scrollToItem(at: IndexPath(item: lastIndex, section: 0), at: .right, animated: false)
}
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
NotificationCenter.default.addObserver(self, selector: #selector(rotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
}
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
// Getting last contentOffset to calculate last index of collectionViewCell
lastIndex = Int(scrollView.contentOffset.x / collectionView.bounds.width)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
// Setting new width of collectionView Cell
return CGSize(width: cellWidthInLandscape, height: collectionView.bounds.size.height)
}
回答10:
Calling viewWillLayoutSubviews is not optimal. Try calling the invalidateLayout() method first.
If you experience the The behaviour of the UICollectionViewFlowLayout is not defined error, you need to verify if all the elements within your view's have changed its sizes, according to a new layout. (see the optional steps within the example code)
Here is the code, to get you started. Depending on the way your UI is created, you may have to experiment to find the right view to call the recalculate method, yet that should guide you towards your first steps.
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
/// (Optional) Additional step 1. Depending on your layout, you may have to manually indicate that the content size of a visible cells has changed
/// Use that step if you experience the `the behavior of the UICollectionViewFlowLayout is not defined` errors.
collectionView.visibleCells.forEach { cell in
guard let cell = cell as? CustomCell else {
print("`viewWillTransition` failed. Wrong cell type")
return
}
cell.recalculateFrame(newSize: size)
}
/// (Optional) Additional step 2. Recalculate layout if you've explicitly set the estimatedCellSize and you'll notice that layout changes aren't automatically visible after the #3
(collectionView.collectionViewLayout as? CustomLayout)?.recalculateLayout(size: size)
/// Step 3 (or 1 if none of the above is applicable)
coordinator.animate(alongsideTransition: { context in
self.collectionView.collectionViewLayout.invalidateLayout()
}) { _ in
// code to execute when the transition's finished.
}
}
/// Example implementations of the `recalculateFrame` and `recalculateLayout` methods:
/// Within the `CustomCell` class:
func recalculateFrame(newSize: CGSize) {
self.frame = CGRect(x: self.bounds.origin.x,
y: self.bounds.origin.y,
width: newSize.width - 14.0,
height: self.frame.size.height)
}
/// Within the `CustomLayout` class:
func recalculateLayout(size: CGSize? = nil) {
estimatedItemSize = CGSize(width: size.width - 14.0, height: 100)
}
/// IMPORTANT: Within the `CustomLayout` class.
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
guard let collectionView = collectionView else {
return super.shouldInvalidateLayout(forBoundsChange: newBounds)
}
if collectionView.bounds.width != newBounds.width || collectionView.bounds.height != newBounds.height {
return true
} else {
return false
}
}
回答11:
It works for me. And this is code in Objective-C:
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
[collectionView.collectionViewLayout invalidateLayout];
}
回答12:
Please understand this
traitCollectionDidChange(previousTraitCollection :) won't be called on iPad when it is rotated, because size class is .regular in both portrait and landscape orientations. There's viewWillTransition(to:with:) that will be called whenever collection view size changes.
Also you shouldn't use UIScreen.mainScreen().bounds if your app supports multitasking as it might not occupy the whole screen, better use collectionView.frame.width for that.
回答13:
I solved the issue using below method
override func viewDidLayoutSubviews() {
if let flowLayout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
collectionView.collectionViewLayout.invalidateLayout()
collectionView.collectionViewLayout = flowLayout
}
}
来源：https://stackoverflow.com/questions/36884376/swift-how-to-refresh-uicollectionview-layout-after-rotation-of-the-device