I'm trying to create a UICollectionView with paging and that each item max width is 250 points, I've managed to create it, but I have 2 problems: The first item start not as it should be, but with more space at start and when I try to swipe, there is always something that wont let me swipe smooth.
This is how it looks:
This is my code:
CenterCellCollectionFlowLayout.swift
class CenterCellCollectionViewFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
var attributesToReturn:[UICollectionViewLayoutAttributes] = super.layoutAttributesForElementsInRect(rect) as! [UICollectionViewLayoutAttributes]
for var i = 0 ; i < attributesToReturn.count ; i++
{
var currentLayoutAttributes: UICollectionViewLayoutAttributes = attributesToReturn[i]
var maximumSpacing: CGFloat = 50
let origin: CGFloat
if i - 1 >= 0 {
let previousLayoutAttributes = attributesToReturn[i - 1]
origin = previousLayoutAttributes.frame.maxX
} else {
origin = 0
}
if origin + maximumSpacing + currentLayoutAttributes.frame.size.width < self.collectionViewContentSize().width
{
var frame: CGRect = currentLayoutAttributes.frame
frame.origin.x = origin + maximumSpacing
currentLayoutAttributes.frame = frame
}
}
return attributesToReturn
}
override func targetContentOffsetForProposedContentOffset(proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
if let cv = self.collectionView {
let cvBounds = cv.bounds
let halfWidth = cvBounds.size.width * 0.5;
let proposedContentOffsetCenterX = proposedContentOffset.x + halfWidth;
if let attributesForVisibleCells = self.layoutAttributesForElementsInRect(cvBounds) as? [UICollectionViewLayoutAttributes] {
var candidateAttributes : UICollectionViewLayoutAttributes?
for attributes in attributesForVisibleCells {
// == Skip comparison with non-cell items (headers and footers) == //
if attributes.representedElementCategory != UICollectionElementCategory.Cell {
continue
}
if let candAttrs = candidateAttributes {
let a = attributes.center.x - proposedContentOffsetCenterX
let b = candAttrs.center.x - proposedContentOffsetCenterX
if fabsf(Float(a)) < fabsf(Float(b)) {
candidateAttributes = attributes;
}
}
else { // == First time in the loop == //
candidateAttributes = attributes;
continue;
}
}
return CGPoint(x : candidateAttributes!.center.x - halfWidth, y : proposedContentOffset.y);
}
}
// Fallback
return super.targetContentOffsetForProposedContentOffset(proposedContentOffset)
}
}
MainViewController.swift
class MainViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
@IBOutlet weak var collectionView: UICollectionView!
@IBOutlet weak var collectionViewFlowLayout: CenterCellCollectionViewFlowLayout!
var collectionObjects: NSMutableArray?
private let reuseIdentifier = "CollectionViewCell"
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
self.collectionView.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath)
{
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
{
let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! UICollectionViewCell
cell.backgroundColor = UIColor.greenColor()
// Configure the cell
return cell
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{
return 10
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets
{
return UIEdgeInsetsMake(0, 0, 0, 0)
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize
{
return CGSizeMake(250, 250)
}
}
Thanks in advance
So I figure out how to do it.
First create a custom UICollectionViewFlowLayout and add this override this method:
override func targetContentOffsetForProposedContentOffset(proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
if let cv = self.collectionView {
let cvBounds = cv.bounds
let halfWidth = cvBounds.size.width * 0.5;
let proposedContentOffsetCenterX = proposedContentOffset.x + halfWidth;
if let attributesForVisibleCells = self.layoutAttributesForElementsInRect(cvBounds) as? [UICollectionViewLayoutAttributes] {
var candidateAttributes : UICollectionViewLayoutAttributes?
for attributes in attributesForVisibleCells {
// == Skip comparison with non-cell items (headers and footers) == //
if attributes.representedElementCategory != UICollectionElementCategory.Cell {
continue
}
if let candAttrs = candidateAttributes {
let a = attributes.center.x - proposedContentOffsetCenterX
let b = candAttrs.center.x - proposedContentOffsetCenterX
if fabsf(Float(a)) < fabsf(Float(b)) {
candidateAttributes = attributes;
}
}
else { // == First time in the loop == //
candidateAttributes = attributes;
continue;
}
}
return CGPoint(x : candidateAttributes!.center.x - halfWidth, y : proposedContentOffset.y);
}
}
// Fallback
return super.targetContentOffsetForProposedContentOffset(proposedContentOffset)
}
Then on the class that you implement the UICollectionView do like that:
let collectionViewLayout: CenterCellCollectionViewFlowLayout = CenterCellCollectionViewFlowLayout()
collectionViewLayout.itemSize = CGSizeMake(self.itemSize, self.itemSize)
collectionViewLayout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
collectionViewLayout.minimumInteritemSpacing = 0
collectionViewLayout.minimumLineSpacing = self.itemSpacing
collectionViewLayout.scrollDirection = UICollectionViewScrollDirection.Horizontal
var collectionView: UICollectionView = UICollectionView(frame: self.collectionContainer.bounds, collectionViewLayout: collectionViewLayout)
collectionView.delegate = self;
collectionView.dataSource = self;
collectionView.backgroundColor = UIColor.redColor()
collectionView.registerClass(LevelsCustomCell.self, forCellWithReuseIdentifier: reuseIdentifier)
collectionView.registerNib(UINib(nibName: reuseIdentifier, bundle: nil), forCellWithReuseIdentifier: reuseIdentifier)
self.collectionContainer.addSubview(collectionView)
Thats about it, works like a charm.