UICollectionView中Cell左对齐 居中 右对齐

最近在开发软件的时候被产品经理要求,要让UICollectionView上面的cell之间的距离要被固定,但是cell得宽度不一定,所以一行有几个cell其实不固定,所以其实cell之间的间距不一定,cell之间最终距离不是你设置的,而是由系统把一行中cell宽度减去,剩下的空白格平均分配的.所以我一开始写出来的效果看起来不是很规则

所以喽,产品经理不同意这样,说看起来不是很规则，然后只能去网上找,做种找到了别人的一些例子，最终弄出来一个貌似还能看的规则。

最近需求还没下来，所以把很久之前的这个代码给重新折腾了一下，支持靠左，居中，靠右，等间距对齐。整体逻辑也比之前清晰了一些。

#import <UIKit/UIKit.h>
typedef NS_ENUM(NSInteger,AlignType){
    AlignWithLeft,
    AlignWithCenter,
    AlignWithRight
};
@interface JYEqualCellSpaceFlowLayout : UICollectionViewFlowLayout
//两个Cell之间的距离
@property (nonatomic,assign)CGFloat betweenOfCell;
//cell对齐方式
@property (nonatomic,assign)AlignType cellType;

-(instancetype)initWthType : (AlignType)cellType;
//全能初始化方法 其他方式初始化最终都会�走到这里
-(instancetype)initWithType:(AlignType) cellType betweenOfCell:(CGFloat)betweenOfCell;

@end

#import "JYEqualCellSpaceFlowLayout.h"
@interface JYEqualCellSpaceFlowLayout(){
    //在居中对齐的时候需要知道这行所有cell的宽度总和
    CGFloat _sumCellWidth ;
}
@end

@implementation JYEqualCellSpaceFlowLayout
-(instancetype)init{
    return [self initWithType:AlignWithCenter betweenOfCell:5.0];
}
-(void)setBetweenOfCell:(CGFloat)betweenOfCell{
    _betweenOfCell = betweenOfCell;
    self.minimumInteritemSpacing = betweenOfCell;
}
-(instancetype)initWthType:(AlignType)cellType{
    return [self initWithType:cellType betweenOfCell:5.0];
}
-(instancetype)initWithType:(AlignType)cellType betweenOfCell:(CGFloat)betweenOfCell{
    self = [super init];
    if (self){
        self.scrollDirection = UICollectionViewScrollDirectionVertical;
        self.minimumLineSpacing = 5;
        self.minimumInteritemSpacing = 5;
        self.sectionInset = UIEdgeInsetsMake(5, 5, 5, 5);
        _betweenOfCell = betweenOfCell;
        _cellType = cellType;
    }
    return self;
}
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
    NSArray * layoutAttributes_t = [super layoutAttributesForElementsInRect:rect];
    NSArray * layoutAttributes = [[NSArray alloc]initWithArray:layoutAttributes_t copyItems:YES];
    //用来临时存放一行的Cell数组
    NSMutableArray * layoutAttributesTemp = [[NSMutableArray alloc]init];
    for (NSUInteger index = 0; index < layoutAttributes.count ; index++) {
        
        UICollectionViewLayoutAttributes *currentAttr = layoutAttributes[index]; // 当前cell的位置信息
        UICollectionViewLayoutAttributes *previousAttr = index == 0 ? nil : layoutAttributes[index-1]; // 上一个cell 的位置信
        UICollectionViewLayoutAttributes *nextAttr = index + 1 == layoutAttributes.count ?
        nil : layoutAttributes[index+1];//下一个cell 位置信息
        
        //加入临时数组
        [layoutAttributesTemp addObject:currentAttr];
        _sumCellWidth += currentAttr.frame.size.width;
        
        CGFloat previousY = previousAttr == nil ? 0 : CGRectGetMaxY(previousAttr.frame);
        CGFloat currentY = CGRectGetMaxY(currentAttr.frame);
        CGFloat nextY = nextAttr == nil ? 0 : CGRectGetMaxY(nextAttr.frame);
        //如果当前cell是单独一行
        if (currentY != previousY && currentY != nextY){
            if ([currentAttr.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
                [layoutAttributesTemp removeAllObjects];
                _sumCellWidth = 0.0;
            }else if ([currentAttr.representedElementKind isEqualToString:UICollectionElementKindSectionFooter]){
                [layoutAttributesTemp removeAllObjects];
                _sumCellWidth = 0.0;
            }else{
                [self setCellFrameWith:layoutAttributesTemp];
            }
        }
        //如果下一个cell在本行，这开始调整Frame位置
        else if( currentY != nextY) {
            [self setCellFrameWith:layoutAttributesTemp];
        }
    }
    return layoutAttributes;
}
//调整属于同一行的cell的位置frame
-(void)setCellFrameWith:(NSMutableArray*)layoutAttributes{
    CGFloat nowWidth = 0.0;
    switch (_cellType) {
        case AlignWithLeft:
            nowWidth = self.sectionInset.left;
            for (UICollectionViewLayoutAttributes * attributes in layoutAttributes) {
                CGRect nowFrame = attributes.frame;
                nowFrame.origin.x = nowWidth;
                attributes.frame = nowFrame;
                nowWidth += nowFrame.size.width + self.betweenOfCell;
            }
            _sumCellWidth = 0.0;
            [layoutAttributes removeAllObjects];
            break;
            
        case AlignWithCenter:
            nowWidth = (self.collectionView.frame.size.width - _sumCellWidth - ((layoutAttributes.count - 1) * _betweenOfCell)) / 2;
            for (UICollectionViewLayoutAttributes * attributes in layoutAttributes) {
                CGRect nowFrame = attributes.frame;
                nowFrame.origin.x = nowWidth;
                attributes.frame = nowFrame;
                nowWidth += nowFrame.size.width + self.betweenOfCell;
            }
            _sumCellWidth = 0.0;
            [layoutAttributes removeAllObjects];
            break;
            
        case AlignWithRight:
            nowWidth = self.collectionView.frame.size.width - self.sectionInset.right;
            for (NSInteger index = layoutAttributes.count - 1 ; index >= 0 ; index-- ) {
                UICollectionViewLayoutAttributes * attributes = layoutAttributes[index];
                CGRect nowFrame = attributes.frame;
                nowFrame.origin.x = nowWidth - nowFrame.size.width;
                attributes.frame = nowFrame;
                nowWidth = nowWidth - nowFrame.size.width - _betweenOfCell;
            }
            _sumCellWidth = 0.0;
            [layoutAttributes removeAllObjects];
            break;
    }
}

@end

OC版本的Demo在这里
------------------------------------------------------分界线-----------------------------------------------------
下面是Swift版本的代码

import UIKit
enum AlignType : NSInteger {
    case left = 0
    case center = 1
    case right = 2
}
class JYEqualCellSpaceFlowLayout: UICollectionViewFlowLayout {
    //两个Cell之间的距离
    var betweenOfCell : CGFloat{
        didSet{
            self.minimumInteritemSpacing = betweenOfCell
        }
    }
    //cell对齐方式
    var cellType : 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 sumCellWidth : CGFloat = 0.0
    
    override init() {
        betweenOfCell = 5.0
        super.init()
        scrollDirection = UICollectionViewScrollDirection.vertical
        minimumLineSpacing = 5
        sectionInset = UIEdgeInsetsMake(5, 5, 5, 5)
    }
    convenience init(_ cellType:AlignType){
        self.init()
        self.cellType = cellType
    }
    convenience init(_ cellType: AlignType, _ betweenOfCell: CGFloat){
        self.init()
        self.cellType = cellType
        self.betweenOfCell = betweenOfCell
    }
    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{
            
            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)
            sumCellWidth += 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 == UICollectionElementKindSectionHeader{
                    layoutAttributes_t.removeAll()
                    sumCellWidth = 0.0
                }else if currentAttr.representedElementKind == UICollectionElementKindSectionFooter{
                    layoutAttributes_t.removeAll()
                    sumCellWidth = 0.0
                }else{
                    self.setCellFrame(with: layoutAttributes_t)
                    layoutAttributes_t.removeAll()
                    sumCellWidth = 0.0
                }
            }else if currentY != nextY{
                self.setCellFrame(with: layoutAttributes_t)
                layoutAttributes_t.removeAll()
                sumCellWidth = 0.0
            }
        }
        return layoutAttributes
    }
    
    /// 调整Cell的Frame
    ///
    /// - Parameter layoutAttributes: layoutAttribute 数组
    func setCellFrame(with layoutAttributes : [UICollectionViewLayoutAttributes]){
        var nowWidth : CGFloat = 0.0
        switch cellType {
        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.betweenOfCell
            }
            break;
        case AlignType.center:
            nowWidth = (self.collectionView!.frame.size.width - sumCellWidth - (CGFloat(layoutAttributes.count - 1) * betweenOfCell)) / 2
            for attributes in layoutAttributes{
                var nowFrame = attributes.frame
                nowFrame.origin.x = nowWidth
                attributes.frame = nowFrame
                nowWidth += nowFrame.size.width + self.betweenOfCell
            }
            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 - betweenOfCell
            }
            break;
        }
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Swift版本Demo在这里