demo for simple Custom UICollectionViewFlowLayout with decoratorView

CustomUICollectionViewFlowLayout.swift

// Playground - noun: a place where people can play

import UIKit

extension UIColor{
    convenience init(hex:Int){
        let red =  CGFloat((hex >> 16) & 0xff) / 255.0
        let green = CGFloat((hex >> 8) & 0xff) / 255.0
        let blue = CGFloat( hex & 0xff) / 255.0
        self.init(red:red,green:green,blue:blue,alpha:1)
    }
}
let textSource = [
    "是故意的吗"
    ,"是我得罪谁了吗"
    ,"这一天竟然每件事情都失算"
    ,"只想转个弯"
    ,"却绕到了飞机场"
    ,"发现没钱在身上"
    ,"乌云乌云快走开"
]

func choice<T>(arr:[T]) -> T{
    return arr[ random() % arr.count ]
}

func demoTitle() ->String {
    return choice(textSource)
}

func demoSummary() -> String{
    var maxCount = random() % 5 + 2
    var sumary = ""
    while maxCount > 0{
        sumary += choice(textSource)
        maxCount--
    }
    return sumary
}

class Topic{
    var title=""
    var summary = ""
    init(title:String,summary:String){
        self.title = title
        self.summary = summary
    }
    
    convenience init(){
        self.init(title:demoTitle(),summary:demoSummary())
    }
}

let redColor =  UIColor(hex: 0xda1c5c)
let blueColor = UIColor(hex: 0x117fbb)
let greenColor = UIColor(hex: 0x169f8c)
let colors = [ redColor,blueColor,greenColor ]
let secondaryTextColor = UIColor(hex: 0xb6b6b6)
let backgroundColor = UIColor(hex: 0xefefef)
func primaryColor() -> UIColor{
    return colors[ random() % colors.count ]
}


class TopicView:UICollectionViewCell{
    let title = UILabel()
    let summary = UILabel()
    class var identifier:String{
        return "TopicView"
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
       setup()
    }

    required init(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
   
    func setup(){
        contentView.layer.borderWidth = 1
        contentView.layer.cornerRadius = 8
        contentView.backgroundColor = UIColor.whiteColor()
        contentScaleFactor = 2
        contentView.contentScaleFactor = 2
        title.contentScaleFactor = 2
       
        title.font = UIFont.italicSystemFontOfSize(14)
        title.numberOfLines = 1
        title.lineBreakMode = .ByTruncatingTail
        summary.textColor = secondaryTextColor
        summary.font = UIFont.systemFontOfSize(12)
        summary.numberOfLines = 2
        summary.lineBreakMode = .ByTruncatingTail
        
        
        contentView.addSubview(title)
        contentView.addSubview(summary)
        title.setTranslatesAutoresizingMaskIntoConstraints(false)
        summary.setTranslatesAutoresizingMaskIntoConstraints(false)
        let sbConstraint = NSLayoutConstraint(item: summary, attribute: .Bottom, relatedBy: .Equal, toItem: contentView, attribute: .Bottom, multiplier: 1, constant: -8)
        let slConstraint  = NSLayoutConstraint(item: summary, attribute: .Leading, relatedBy: .Equal, toItem: contentView, attribute: .Leading, multiplier: 1, constant: 8)
        let srConstraint = NSLayoutConstraint(item: summary, attribute:.Trailing , relatedBy: .Equal, toItem: contentView, attribute: .Trailing, multiplier: 1, constant: -8)
        
        let tbConstraint = NSLayoutConstraint(item: title, attribute: .Bottom, relatedBy: .Equal, toItem: summary, attribute: .Top, multiplier: 1, constant: -8)
        let tlConstraint = NSLayoutConstraint(item: title, attribute: .Leading, relatedBy: .Equal, toItem: summary, attribute: .Leading, multiplier: 1, constant: 0)
        let trConstraint = NSLayoutConstraint(item: title, attribute: .Trailing, relatedBy: .Equal, toItem: contentView, attribute: .Trailing, multiplier: 1, constant: -20)
        
        contentView.addConstraint(sbConstraint)
        contentView.addConstraint(slConstraint)
        contentView.addConstraint(srConstraint)
        contentView.addConstraint(tbConstraint)
        contentView.addConstraint(tlConstraint)
        contentView.addConstraint(trConstraint)
        
    }
    func bind(topic:Topic){
       title.text = topic.title
        summary.text = topic.summary
        let color = primaryColor()
        title.textColor = color
        contentView.layer.borderColor = color.CGColor
        
        contentView.layoutIfNeeded()
    }
}
// debug TopicView
//let topicView = TopicView(frame: CGRect(x: 0, y: 0, width: 240, height: 80))
//topicView.bind(Topic())

class TopicDataSource :NSObject,UICollectionViewDataSource{
    var topics:[Topic] = []
    
    override init() {
        super.init()
        generateDemoData()
    }
    
    func generateDemoData(){
       var maxCount = random() %  1 + 3
        while maxCount > 0 {
           topics.append(Topic())
            maxCount--
        }
    }
    
    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int{
       return topics.count
    }
    
    // The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell{
        let topicView =  collectionView.dequeueReusableCellWithReuseIdentifier(TopicView.identifier, forIndexPath: indexPath) as TopicView
        topicView.bind(topicAtIndexPath(indexPath))
        return topicView
    }
    
    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int{
        return 1
    }
    
    // MARK: Helper
    func topicAtIndexPath(indexPath:NSIndexPath) -> Topic{
        return topics[indexPath.item]
    }
}

class SeperatorView: UICollectionReusableView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    required init(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func setup(){
        backgroundColor = primaryColor()
    }
}
class TopicFlowLayout:UICollectionViewFlowLayout{
    struct LayoutKinds {
        static let globalHeader = "globalHeader"
        static let seperator = "seperator"
    }
    
    var seperatorLayoutInfo:[NSIndexPath:UICollectionViewLayoutAttributes] = [:]
 
    override func prepareLayout() {
        super.prepareLayout()
        registerClass(SeperatorView.classForCoder(), forDecorationViewOfKind: LayoutKinds.seperator)
        
        sectionInset = UIEdgeInsets(top: 36, left: 20, bottom: 36, right: 20)
        itemSize = CGSize(width: collectionView!.bounds.width - 40, height: 96)
        
        var layoutInfo:[NSIndexPath:UICollectionViewLayoutAttributes] = [:]
        let sections = collectionView!.numberOfSections()
        for section in Range(start: 0, end: sections){
            let items = collectionView!.numberOfItemsInSection(section)
            for item in Range(start: 0, end: items){
                // ignoreLast
                if item == (items - 1){
                    continue
                }
                let indexPath = NSIndexPath(forItem: item, inSection: section)
                layoutInfo[indexPath] = layoutAttributesForSeperatorAtIndexPath(indexPath)
            }
        }
        
        seperatorLayoutInfo = layoutInfo
        println("prepareLayout")
    }
    
   
    override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
        var attrsArray = super.layoutAttributesForElementsInRect(rect)
        for attrs in seperatorLayoutInfo.values{
            if attrs.frame.intersects(rect){
                attrsArray?.append(attrs)
            }
        }
        return attrsArray
    }
    
   
    override func layoutAttributesForDecorationViewOfKind(elementKind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes! {
        return seperatorLayoutInfo[indexPath]
    }
    
    // MARK:Helpers
    func layoutAttributesForSeperatorAtIndexPath(indexPath:NSIndexPath) -> UICollectionViewLayoutAttributes{
        let cellAttributes = layoutAttributesForItemAtIndexPath(indexPath)
        let nextIndexPath = NSIndexPath(forItem: indexPath.item + 1, inSection: indexPath.section)
        let nextCellAttributes = layoutAttributesForItemAtIndexPath(nextIndexPath)
        var layoutAttributes = UICollectionViewLayoutAttributes(forDecorationViewOfKind: LayoutKinds.seperator, withIndexPath: indexPath)
        
        let strokeWidth:CGFloat = 2;
        let baseFrame = cellAttributes.frame
        let lineSpacing = nextCellAttributes.frame.minY - baseFrame.maxY
        let y = baseFrame.maxY + (lineSpacing - strokeWidth ) * 0.5
        let frame = CGRect(x: baseFrame.origin.x, y: y, width: baseFrame.width, height: strokeWidth)
        layoutAttributes.frame = frame
        return layoutAttributes
    }
}
let dataSource = TopicDataSource()
let layout = TopicFlowLayout()
let frame = CGRect(x: 0, y: 0, width: 320, height: 480)
let collectionView = UICollectionView(frame: frame, collectionViewLayout: layout)
collectionView.registerClass(TopicView.classForCoder(), forCellWithReuseIdentifier: TopicView.identifier)
collectionView.backgroundColor = backgroundColor
collectionView.dataSource = dataSource