UICollectionView

一、cell复用的collectionView：
1.HomeRecommendView.swift 文件 & HomeRecommendView.xib 文件：

import UIKit

class HomeRecommendView: UIView {

    @IBOutlet weak var collectionView: UICollectionView!
    
    var selectBlock:((Int)->())?
    
    lazy var layout: UICollectionViewFlowLayout = {
        let layout = UICollectionViewFlowLayout()
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
        layout.sectionInset = UIEdgeInsets.init(top: 10, left: 16, bottom: 10, right: 16)
        layout.scrollDirection = .horizontal
        layout.itemSize = CGSize.init(width: kScreenWidth / 3.0, height: 119.5)
        return layout
    }()
    
    var dataSource: [HomeBookReadModel]? {
        didSet {
            guard dataSource != nil  else {
                return
            }
            collectionView.reloadData()
        }
    }
    
    override func awakeFromNib() {
        collectionView.delegate = self
        collectionView.dataSource = self
        let nib = UINib(nibName: "HomeRecommendCollectionCell", bundle: nil)
        collectionView.register(nib, forCellWithReuseIdentifier: "HomeRecommendCollectionCell")
        collectionView.setCollectionViewLayout(layout, animated: true)
       }
    
}


// MARK: - UICollectionViewDelegate,UICollectionViewDataSource
extension HomeRecommendView: UICollectionViewDelegate,UICollectionViewDataSource {
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return dataSource?.count ?? 0
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HomeRecommendCollectionCell", for: indexPath) as! HomeRecommendCollectionCell
        let model = dataSource?[indexPath.row]
        cell.model = model
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        selectBlock?(indexPath.row)
    }
    
}

• 代码实现collectionView:

lazy var collectionView: UICollectionView = {
        let frame = CGRect.init(x: 0, y: 0, width: self.view.bounds.size.width, height:kScreenHeight)
        let collectionView = UICollectionView(frame: frame, collectionViewLayout: self.layout)
        collectionView.backgroundColor = UIColor.white
        collectionView.delegate = self
        collectionView.dataSource = self
        return collectionView
    }()

2.自定义 HomeRecommendCollectionCell.swift 文件 & HomeRecommendCollectionCell.xib 文件

二、sizeForItem 动态改变：
如果想让 item 的宽高自适应，则不需要在创建 UICollectionViewFlowLayout 实例的时候设置 layout.itemSize ，只需要遵循 UICollectionViewDelegateFlowLayout 代理，重写 sizeForItemAt 代理方法即可。

extension ReleaseEvaluationThirdCell: UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout {

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let model = self.dataSource?[indexPath.row]
        return model?.itemSize ?? CGSize.init(width: 0, height: 0)
    }
    
    //如果写了 layout.minimumLineSpacing = 20 可以不写这个代理方法
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 20
    }
    
    //如果写了 layout.minimumInteritemSpacing = 20 可以不写这个代理方法
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 20
    }
   
}

• 注：这种方法的效果并不好，并不能让所有item之间的左右间距固定，想要左右间距固定，需要重写 UICollectionViewFlowLayout 类。

效果图.png

三、增加header、footer:

• 注释：在collectionView中，并不像tableView一样，有tableViewHeader、tableViewFooter，只能添加到section的header、footer上，并且必须实现 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) 代理方法，header才能正常展示，当不想显示header的时候，需要 return CGSize.zero 。

//注册header
collectionView.register(BookMuseumChineseHeaderView.self, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, withReuseIdentifier: "BookMuseumChineseHeaderView")


//MARK: - UICollectionViewDelegate,UICollectionViewDataSource
extension BookMuseumChineseController: UICollectionViewDelegate,UICollectionViewDataSource {
    
    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
        if kind == UICollectionElementKindSectionHeader {
            let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "BookMuseumChineseHeaderView", for: indexPath) as! BookMuseumChineseHeaderView
            headerView.dataSource = self.headerModel
            return headerView
        }
        return UICollectionReusableView()
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
        if self.dataModel?.booklist != nil {
            return CGSize(width: collectionView.frame.size.width, height: self.dataModel?.headerHeight ?? 0)
        } else {
            return CGSize.zero
        }
    }
   
}