CalendarCell.swift

import UIKit

class CalendarCell: UICollectionViewCell {
    public var textLabel:UILabel!
    
    required init(coder aDecoder:NSCoder){
        super.init(coder: aDecoder)!
    }
    
    override init(frame:CGRect){
        super.init(frame:frame)
        //UILabelを生成
        textLabel = UILabel()
        textLabel.frame = CGRect(x:0,y:0,width:self.frame.width,height:self.frame.height)
        textLabel.textAlignment = .center
        
        self.contentView.addSubview(textLabel!)
        
    }
}

CalendarView.swift

import UIKit

@objc protocol CalendarViewDelegate {
    func changeMonth(_ text:String)
}

class CalendarView: UICollectionView{
    
    //セルの余白
    let cellMargin:CGFloat = 2.0
    let dateManager = DateManager()
    //１週間に何日あるか(行数)
    let daysPerWeek:Int = 7
    var startDate:Date!
    
    var calendarDelegate:CalendarViewDelegate!
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
        self.register(CalendarCell.self, forCellWithReuseIdentifier: "collectCell")
        self.delegate = self
        self.dataSource = self
        self.backgroundColor = .white
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let visibleCell = self.visibleCells.filter{
            return self.bounds.contains($0.frame)
        }
        
        var visibleCellTag = Array<Int>()
        if(visibleCell != []){
            visibleCellTag = visibleCell.map{$0.tag}
            //月は奇数か偶数か　割り切れるものだけを取り出す
            let even = visibleCellTag.filter{
                return $0 % 2 == 0
            }
            let odd = visibleCellTag.filter{
                return $0 % 2 != 0
            }
            //oddかevenの多い方を返す
            let month = even.count >= odd.count ? even[0] : odd[0]
            
            //桁数によって分岐
            let digit = numberOfDigit(month: month)
            var text = ""
            if(digit == 5){
                text = String(month / 10) + "年" + String(month % 10) + "月"
            }else if(digit == 6){
                text = String(month / 100) + "年" + String(month % 100) + "月"
            }
            if calendarDelegate != nil {
                calendarDelegate.changeMonth(text)
            }
        }
    }
    
    func numberOfDigit(month:Int) -> Int{
        var num = month
        var cnt = 1
        while(num / 10 != 0){
            cnt = cnt + 1
            num = num / 10
        }
        return cnt
        
    }
    
}

extension CalendarView:UICollectionViewDelegate {
    //選択した時
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        
    }
}

extension CalendarView: UICollectionViewDataSource {
    
    //セクションの数
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    
    //セルの総数
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return dateManager.cellCount(startDate:startDate)
    }
    
    //セルの設定
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell:CalendarCell = collectionView.dequeueReusableCell(withReuseIdentifier:"collectCell",for:indexPath as IndexPath) as! CalendarCell
        
        //土曜日は赤　日曜日は青　にテキストカラーを変更する
        if(indexPath.row % 7 == 0){
            cell.textLabel.textColor = UIColor.red
        }else if(indexPath.row % 7 == 6){
            cell.textLabel.textColor = UIColor.blue
        }else{
            cell.textLabel.textColor = UIColor.gray
        }
        cell.tag = Int(dateManager.monthTag(row:indexPath.row,startDate:startDate))!
        //セルの日付を取得し
        cell.textLabel.text = dateManager.conversionDateFormat(row:indexPath.row,startDate:startDate)
        
        //セルの日付を取得
        let day = Int(dateManager.conversionDateFormat(row:indexPath.row,startDate:startDate!))!
        if(day == 1){
            cell.textLabel.border(positions:[.Top,.Left],borderWidth:1,borderColor:UIColor.black)
        }else if(day <= 7){
            cell.textLabel.border(positions:[.Top],borderWidth:1,borderColor:UIColor.black)
        }else{
            cell.textLabel.border(positions:[.Top],borderWidth:0,borderColor:UIColor.white)
        }
        return cell
    }
}

extension CalendarView: UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView:UICollectionView,layout collectionViewLayout:UICollectionViewLayout,minimumLineSpacingForSectionAt section:Int) -> CGFloat{
        return cellMargin
    }
    
    func collectionView(_ collectionView:UICollectionView,layout collectionViewLayout:UICollectionViewLayout,minimumInteritemSpacingForSectionAt section:Int) -> CGFloat{
        return cellMargin
    }
    
    
    //セルのサイズを設定
    func collectionView(_ collectionView:UICollectionView,layout collectionViewLayout:UICollectionViewLayout,sizeForItemAt indexPath:IndexPath) -> CGSize{
        let numberOfMargin:CGFloat = 8.0
        let width:CGFloat = (collectionView.frame.size.width - cellMargin * numberOfMargin) / CGFloat(daysPerWeek)
        let height:CGFloat = width * 2.0
        return CGSize(width:width,height:height)
    }
}

CalendarViewController.swift

import UIKit

class CalendarViewController: UIViewController {

    var monthLabel:UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let barHeight = UIApplication.shared.statusBarFrame.size.height
        let width = self.view.frame.width
        let height = self.view.frame.height
        let layout = UICollectionViewFlowLayout()
        layout.sectionInset = UIEdgeInsetsMake(0,0,0,0)
        
        //コレクションビューを設置していくよ
        let calendarFrame = CGRect(x:0,y:barHeight + 50,width:width,height:height - barHeight - 50)
        let calendarView = CalendarView(frame: calendarFrame, collectionViewLayout: layout)
        calendarView.calendarDelegate = self
        self.view.addSubview(calendarView)
        
        let startMonth = 10
        let startYear = 2015
        var components = Calendar.current.dateComponents([.year ,.month, .day], from:Date())
        components.day = 1
        components.month = startMonth
        components.year = startYear
        let startDate = Calendar.current.date(from: components)
        calendarView.startDate = startDate
        
        //年月ラベル
        monthLabel = UILabel()
        monthLabel.frame = CGRect(x:0,y:0,width:width,height:100)
        monthLabel.center = CGPoint(x:width / 2,y:50)
        monthLabel.textAlignment = .center
        
        monthLabel.text = "\(startYear)年\(startMonth)月"
        self.view.addSubview(monthLabel)
    }

}

extension CalendarViewController: CalendarViewDelegate {
    func changeMonth(_ text: String) {
        self.monthLabel.text = text
    }
    
    
}

DateManager.swift

import UIKit

class DateManager {
    
    //現在の日付
    private var selectedDate = Date()
    
    //１週間に何日あるか
    private let daysPerWeek:Int = 7
    
    //セルの個数(nilが入らないようにする)
    private var numberOfItems:Int = 0
    
    /*      指定した月から現在の月までのセルの数を返すメソッド
     ** 引数　-> startDate 指定した月 カレンダーを始める月
     ** return -> セルの総数
      */
    func cellCount(startDate:Date) -> Int{
        //startDate(1番最初の日時)の年月を取り出す
        let startDateComponents = Calendar.current.dateComponents([.year ,.month], from:startDate)
        
        //currentDate(現在の日時)の年月を取り出す
        let currentDateComponents = Calendar.current.dateComponents([.year ,.month], from:selectedDate)
        
        //startDateとcurrentDateが何ヶ月離れているか fromとtoの差を取り出す
        let components = Calendar.current.dateComponents([.year,.month], from: startDateComponents, to: currentDateComponents)
        
        //startDateとcurrentDateが何ヶ月離れているか計算する
        let numberOfMonth = components.month! + components.year! * 12
        
        //１月ずつ何日あるか見ていく
        for i in 0 ..< numberOfMonth + 1{
            
            //monthをiに設定したdateComponentsを用意し、startDateからi月分足した日付(date)を取得する
            var dateComponents = DateComponents()
            dateComponents.month = i
            let date = Calendar.current.date(byAdding: dateComponents, to: startDate)
            
            //取得した月に週がいくつあるかを取得　in(その月)にof(週)が何個あるか
            let dateRange = Calendar.current.range(of: .weekOfMonth, in: .month, for: date!)
            
            //月の初日が何曜日かを取得 日曜日==1
            let ordinalityOfFirstDay = Calendar.current.ordinality(of: .day, in: .weekOfMonth, for: firstDateOfMonth(date:date!))
            
            //その月の始まりが日曜日かどうかで場合分け
            if(ordinalityOfFirstDay == 1 || i == 0){
                numberOfItems = numberOfItems + dateRange!.count * daysPerWeek
            }else{
                numberOfItems = numberOfItems + (dateRange!.count - 1) * daysPerWeek
            }
        }
        //セルの総数を返す
        return numberOfItems
    }
    
    
    
    /*      指定された月の初日を取得        */
    func firstDateOfMonth(date:Date) -> Date{
        //渡された日時から日にちを１にした日付を返す
        var components = Calendar.current.dateComponents([.year ,.month, .day], from:date)
        components.day = 1
        let firstDateMonth = Calendar.current.date(from: components)
        return firstDateMonth!
    }
    
    
    /*      表記する日にちの取得　週のカレンダー
     ** 引数　row          ->  UICollectionViewのIndexPath.row
     ** startDate    ->  指定した月　カレンダーを始める月
     ** return  date      ->  セルに入れる日付
     */
    func dateForCellAtIndexPathWeeks(row:Int,startDate:Date) -> Date{
        //始まりの日が週の何番目かを計算(日曜日が１) 指定した月の初日から数える
        let ordinalityOfFirstDay = Calendar.current.ordinality(of: .day, in: .weekOfMonth, for: firstDateOfMonth(date:startDate))
        var dateComponents = DateComponents()
        dateComponents.day = row - (ordinalityOfFirstDay! - 1)
        //計算して、基準の日から何日マイナス、加算するか dateComponents.day = -2 とか
        let date = Calendar.current.date(byAdding:dateComponents,to:firstDateOfMonth(date:startDate))
        return date!
    }
    
    
    
    /*      表記の変更 これをセルを作成する時に呼び出す
     引数  row         -> UICollectionViewのIndexPath.row
     startDate   -> 指定した月　カレンダーを始める月
     return  String   -> セルに入れる日付をString型にしたもの
     */
    func conversionDateFormat(row:Int,startDate:Date) -> String{
        let cellDate = dateForCellAtIndexPathWeeks(row: row,startDate:startDate)
        let formatter = DateFormatter()
        formatter.dateFormat = "d"
        return formatter.string(from: cellDate)
        
    }
    
    
    //月を返す
    func monthTag(row:Int,startDate:Date) -> String{
        let cellDate = dateForCellAtIndexPathWeeks(row: row,startDate:startDate)
        let formatter = DateFormatter()
        formatter.dateFormat = "YM"
        return formatter.string(from:cellDate)
    }
    
    
}