使用UICollectionView做tag显示的时候的对齐方式

import UIKit
enum AlignType : NSInteger {
    case left = 0
    case center = 1
    case right = 2
}
class EqualCellSpaceFlowLayout: UICollectionViewFlowLayout {
    //两个Cell之间的距离
    private var horizontalSpace : CGFloat{
        didSet{
            self.minimumInteritemSpacing = horizontalSpace
        }
    }
    //cell对齐方式
    private var alignType : AlignType = AlignType.center
    //在居中对齐的时候需要知道这行所有cell的宽度总和
    var cellWidthInLine : CGFloat = 0.0
    
    override init() {
        horizontalSpace = 5.0
        super.init()
        scrollDirection = UICollectionView.ScrollDirection.vertical
        minimumLineSpacing = 5
        sectionInset = UIEdgeInsets(top: 5, left: 5, bottom: 5, right: 5)
    }
    convenience init(_ cellType:AlignType){
        self.init()
        self.alignType = cellType
    }
    convenience init(_ cellType: AlignType, _ horizontalSpace: CGFloat){
        self.init()
        self.alignType = cellType
        self.horizontalSpace = horizontalSpace
    }
    
    required init?(coder aDecoder: NSCoder) {
        horizontalSpace = 5.0
        super.init(coder: aDecoder)
        scrollDirection = UICollectionView.ScrollDirection.vertical
        minimumLineSpacing = 5
        sectionInset = UIEdgeInsets(top: 5, left: 5, bottom: 5, right: 5)
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        
        let layoutAttributes_super : [UICollectionViewLayoutAttributes] = super.layoutAttributesForElements(in: rect) ?? [UICollectionViewLayoutAttributes]()
        let layoutAttributes:[UICollectionViewLayoutAttributes] = NSArray(array: layoutAttributes_super, copyItems:true)as! [UICollectionViewLayoutAttributes]
        var layoutAttributes_t : [UICollectionViewLayoutAttributes] = [UICollectionViewLayoutAttributes]()
        for index in 0..<layoutAttributes.count{
            
            print("index in 0..<layoutAttributes.count ==============")
            
            let currentAttr = layoutAttributes[index]
            let previousAttr = index == 0 ? nil : layoutAttributes[index-1]
            let nextAttr = index + 1 == layoutAttributes.count ?
                nil : layoutAttributes[index+1]
            
            layoutAttributes_t.append(currentAttr)
            cellWidthInLine += currentAttr.frame.size.width
            
            let previousY :CGFloat = previousAttr == nil ? 0 : previousAttr!.frame.maxY
            let currentY :CGFloat = currentAttr.frame.maxY
            let nextY:CGFloat = nextAttr == nil ? 0 : nextAttr!.frame.maxY
            
            if currentY != previousY && currentY != nextY{
                if currentAttr.representedElementKind == UICollectionView.elementKindSectionHeader{
                    layoutAttributes_t.removeAll()
                    cellWidthInLine = 0.0
                    print("currentAttr.representedElementKind == UICollectionView.elementKindSectionHeader =========== Header")
                }else if currentAttr.representedElementKind == UICollectionView.elementKindSectionFooter{
                    layoutAttributes_t.removeAll()
                    cellWidthInLine = 0.0
                    print("currentAttr.representedElementKind == UICollectionView.elementKindSectionFooter ============ Footer")
                }else{
                    self.setCellFrame(with: layoutAttributes_t)
                    layoutAttributes_t.removeAll()
                    cellWidthInLine = 0.0
                    print("currentY != previousY && currentY != nextY ============== Item")
                }
            } else if currentY != nextY { //这里currentY == previousY 说明和上一个项目在同一行，currentY != nextY说明下一个项目要换行了，这种情况直接计算本行的对齐方式
                self.setCellFrame(with: layoutAttributes_t)
                layoutAttributes_t.removeAll()
                cellWidthInLine = 0.0
                print("currentY != nextY ======== Else")
            }
        }
        return layoutAttributes
    }
    
    /// 调整Cell的Frame
    ///
    /// - Parameter layoutAttributes: layoutAttribute 数组
    func setCellFrame(with layoutAttributes : [UICollectionViewLayoutAttributes]){
        var nowWidth : CGFloat = 0.0
        switch alignType {
        case AlignType.left:
            nowWidth = self.sectionInset.left
            for attributes in layoutAttributes {
                var nowFrame = attributes.frame
                nowFrame.origin.x = nowWidth
                attributes.frame = nowFrame
                nowWidth += nowFrame.size.width + self.horizontalSpace
            }
            break;
        case AlignType.center:
            nowWidth = (self.collectionView!.frame.size.width - cellWidthInLine - (CGFloat(layoutAttributes.count - 1) * horizontalSpace)) / 2
            for attributes in layoutAttributes{
                var nowFrame = attributes.frame
                nowFrame.origin.x = nowWidth
                attributes.frame = nowFrame
                nowWidth += nowFrame.size.width + self.horizontalSpace
            }
            break;
        case AlignType.right:
            nowWidth = self.collectionView!.frame.size.width - self.sectionInset.right
            for var index in 0 ..< layoutAttributes.count{
                index = layoutAttributes.count - 1 - index
                let attributes = layoutAttributes[index]
                var nowFrame = attributes.frame
                nowFrame.origin.x = nowWidth - nowFrame.size.width
                attributes.frame = nowFrame
                nowWidth = nowWidth - nowFrame.size.width - horizontalSpace
            }
            break;
        }
    }
    
    
}

做对齐方式的部分其实就是通过重新UICollectionViewFlowLayout来做的，主要是将每一行的元素按照设定的方向进行排列。

以下给出测试用的源码

import UIKit

class ViewController: UIViewController {

    let list = ["全部","肺癌","甲状腺癌","食管癌","乳腺癌","抠鼻咽喉癌","淋巴瘤","肝胆胰癌","胃癌","结肠直癌","泌尿系统肿瘤","妇科肿瘤","骨肿瘤","一","二","三","四"]
    
    @IBOutlet weak var mCollectionView: UICollectionView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        let layout = EqualCellSpaceFlowLayout(.left)
        mCollectionView.collectionViewLayout = layout
    }


}


extension ViewController: UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout {
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return list.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "tagCell", for: indexPath) as? TagCell
        cell?.name.text = list[indexPath.row]
        return cell!
    }
    
    func collectionView(_ collectionView: UICollectionView?, TextForItemAt indexPath: IndexPath) -> String {
        return list[indexPath.row]
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let attr:[NSAttributedString.Key:Any] = [.font:UIFont.systemFont(ofSize: 12)]
        let width = (list[indexPath.row] as NSString).boundingRect(with: CGSize(width: CGFloat.greatestFiniteMagnitude, height: 30), options: .usesLineFragmentOrigin, attributes: attr, context: nil).width + 5.0
        return CGSize(width: width, height: 30)
    }
}

测试Demo源码地址