IOS UICollectionView 图片展示墙

//put the images in to project
 import UIKit
 2
 3 class ViewController：UIViewController,
 UICollectionViewDataSource, UICollectionViewDelegate {
 4
 5 var images = [“Pic1”, “Pic2”, “Pic3”, “Pic8”, “Pic5”,
 “Pic6”, “Pic7”, “Pic4”, “Pic9”]
 6
 7 override func viewDidLoad() {
 8 super.viewDidLoad()
 9 // Do any additional setup after loading the view,
 typically from a nib.
 10 let screenRect = UIScreen.main.bounds
 11 let rect = CGRect(x：0, y：20, width：
 screenRect.size.width, height：screenRect.size.height - 20)
 12
 13 let flowLayout = UICollectionViewFlowLayout()
 14 flowLayout.itemSize = CGSize(width：155, height：
 15 flowLayout.scrollDirection =
 UICollectionViewScrollDirection.vertical
 16
 17 let collectionView = UICollectionView(frame：rect,
 collectionViewLayout：flowLayout)
 18
 19 collectionView.dataSource = self
 20 collectionView.delegate = self
 21
 collectionView.register(UICollectionViewCell.classForCoder(),
 forCellWithReuseIdentifier： “reusedCell”)
 22 self.view.addSubview(collectionView)
 23 }
 24
 25 func collectionView(_ collectionView：
 UICollectionView, numberOfItemsInSection section：Int) ->
 Int {
 26 return images.count
 27 }
 28
 29 func collectionView(_ collectionView：
 UICollectionView, cellForItemAt indexPath：IndexPath) ->
 UICollectionViewCell {
 30
 31 let identifier = “reusedCell”
 32 let cell =
 collectionView.dequeueReusableCell(withReuseIdentifier：
 identifier, for：indexPath)
 33
 34 let imageView：UIImageView？= cell.viewWithTag(1)
 as？UIImageView
 35 if imageView == nil{
 36 let image = UIImage(named：images[(indexPath as
 NSIndexPath).row])
 37 let imageView = UIImageView(image：image)
 38 imageView.frame = CGRect(x：0, y：0, width：150,
 height：135)
 39 imageView.layer.opacity = 0.5
 40 imageView.tag = 1
 41 cell.addSubview(imageView)
 42 }else{
 43 imageView？.image = UIImage(named：
 images[(indexPath as NSIndexPath).row])
 44 }
 45
 46 return cell
 47 }
 48
 49 func collectionView(_ collectionView：
 UICollectionView, didSelectItemAt indexPath：IndexPath) {
 50 let cell = collectionView.cellForItem(at：indexPath)
 51 let imageView = cell？.viewWithTag(1)
 52 imageView？.layer.opacity = 1.0;
 53 }
 54 }

//UICollectionView包括三个部分：Cells、Supplementary Views、Decoration Views