iOS~ UICollectionView 无缝紧密排列

1、先上图：

`一般排列的间隔`会出现不准确的情况：（间隔10）	而我们想要实现`每个cell以最小间距紧密排列`:
IMG_0024.PNG	IMG_0023.PNG

2、原理：

1、（swift）UICollectionView Cell大小自适应并靠左对齐最简单的实现
 2、（OC）UICollectionView的无缝排序

1、重写一个继承自UICollectionViewFlowLayout类的子类：
复杂的方法是自己写一个UICollectionViewLayout，这里我选择了一种更简单的方法，根据系统的布局来进行调整，创建一个UICollectionViewLeftFlowLayout类继承UICollectionViewFlowLayout，重写layoutAttributesForElements(in rect:CGRect)方法

UICollectionViewFlowLayout.h文件：

@interface New_DictionUICollectionViewLeftFlowLayout : UICollectionViewFlowLayout

@end

UICollectionViewFlowLayout.m文件：

#import "New_DictionUICollectionViewLeftFlowLayout.h"

@implementation New_DictionUICollectionViewLeftFlowLayout


- (NSArray *)layoutAttributesForElementsInRect:(CGRect) rect {
    NSMutableArray *attributes = [[super layoutAttributesForElementsInRect:rect] mutableCopy];
    
    for (UICollectionViewLayoutAttributes *attr in attributes) {
        
        // 每个cell的frame
        NSLog(@"😆😆 = %@", NSStringFromCGRect([attr frame]));
        /*
         数组后发现数据还是有间隔，
         然后确定思路，将里面的数据进行更改就实现了紧密排版
         贴上代码：
         
        2021-10-14 17:42:17.788922+0800 km[6277:377641] 😆😆 = {{15, 5}, {115, 32}}
        2021-10-14 17:42:26.627243+0800 km[6277:377641] 😆😆 = {{197, 5}, {163, 32}}
        2021-10-14 17:42:26.627660+0800 km[6277:377641] 😆😆 = {{15, 47}, {138, 32}}
        2021-10-14 17:42:26.627932+0800 km[6277:377641] 😆😆 = {{189.5, 47}, {86, 32}}
        2021-10-14 17:42:26.628892+0800 km[6277:377641] 😆😆 = {{312, 47}, {48, 32}}
        2021-10-14 17:42:26.629597+0800 km[6277:377641] 😆😆 = {{15, 89}, {92, 32}}
        2021-10-14 17:42:26.630260+0800 km[6277:377641] 😆😆 = {{117, 89}, {90, 32}}
         */
    }
    
    
    for (UICollectionViewLayoutAttributes *attr in attributes) {
        NSLog(@"%@", NSStringFromCGRect([attr frame]));
    }
    
    /// 下面代码，设置后，就会实现自己想要的结果了：
    //从第二个循环到最后一个
    for(int i = 1; i < [attributes count]; ++i) {
        //当前attributes
        UICollectionViewLayoutAttributes *currentLayoutAttributes = attributes[i];
        //上一个attributes
        UICollectionViewLayoutAttributes *prevLayoutAttributes = attributes[i - 1];
        //我们想设置的最大间距，可根据需要改
        NSInteger maximumSpacing = [UIScreen mainScreen].bounds.size.width/375*10;
        //前一个cell的最右边
        NSInteger origin = CGRectGetMaxX(prevLayoutAttributes.frame);
        //如果当前一个cell的最右边加上我们想要的间距加上当前cell的宽度依然在contentSize中，我们改变当前cell的原点位置
        //不加这个判断的后果是，UICollectionView只显示一行，原因是下面所有cell的x值都被加到第一行最后一个元素的后面了
        if(origin + maximumSpacing + currentLayoutAttributes.frame.size.width < self.collectionViewContentSize.width) {
            CGRect frame = currentLayoutAttributes.frame;
            frame.origin.x = origin + maximumSpacing;
            currentLayoutAttributes.frame = frame;
        }
        /*
        /// 注意：（当前的cell宽度要加上当前这个cell右边的间隔后，再判断是否一行是否能放开，+ [UIScreen mainScreen].bounds.size.width/375*10）
        //如果当前一个cell的最右边加上我们想要的间距加上当前cell的宽度依然在contentSize中，我们改变当前cell的原点位置（当前的cell宽度要加上当前这个cell右边的间隔）
        //不加这个判断的后果是，UICollectionView只显示一行，原因是下面所有cell的x值都被加到第一行最后一个元素的后面了
        if(origin + maximumSpacing + currentLayoutAttributes.frame.size.width + [UIScreen mainScreen].bounds.size.width/375*10 < self.collectionViewContentSize.width) {
            CGRect frame = currentLayoutAttributes.frame;
            frame.origin.x = origin + maximumSpacing;
            currentLayoutAttributes.frame = frame;
        }
        */
    }

    return attributes;

    
    
    return [attributes copy];
}


@end

2、使用：

- (void)setupUI {
    
//    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    /// 重写一个继承自UICollectionViewFlowLayout类的子类：
    New_DictionUICollectionViewLeftFlowLayout *layout = [[New_DictionUICollectionViewLeftFlowLayout alloc] init];
    
    layout.scrollDirection = UICollectionViewScrollDirectionVertical;
    layout.sectionHeadersPinToVisibleBounds = NO;
    layout.sectionFootersPinToVisibleBounds = NO;
    
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
    collectionView.backgroundColor = [UIColor whiteColor];
    collectionView.delegate = self;
    collectionView.dataSource = self;
    collectionView.showsVerticalScrollIndicator = NO;
    collectionView.scrollEnabled = NO;
    [self addSubview:collectionView];
    [collectionView makeConstraints:^(MASConstraintMaker *make) {
        //make.edges.equalTo(self);
        make.top.bottom.equalTo(self);
        make.left.mas_equalTo(self.mas_left).offset([UIScreen mainScreen].bounds.size.width/375*15);
        make.right.mas_equalTo(self.mas_right).offset(-[UIScreen mainScreen].bounds.size.width/375*14);
    }];
    [collectionView registerClass:[N_DictionaryPanelRecordCell class] forCellWithReuseIdentifier:NSStringFromClass([N_DictionaryPanelRecordCell class])];
    self.collectionView = collectionView;
    
}

- (void)refreshCollectionView {
    [self.collectionView reloadData];
}

#pragma mark -- <UICollectionViewDelegate>
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 1;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return self.searchArray.count;
}

-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    
    CGFloat width = 0;
    CGFloat height = 0;
    
    if (self.searchArray.count > 0) {
        // 根据字符串的长度，来设置宽度
        NSString *itemString = [NSString stringWithFormat:@"%@", self.searchArray[indexPath.row][@"word"]];
        if (itemString.length > 0 && ![itemString isEqualToString:@"(null)"] && ![itemString isEqualToString:@"<null>"]) {
            //（单行文本）
            CGSize size = [itemString sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:[UIScreen mainScreen].bounds.size.width/375*15 weight:UIFontWeightRegular]}];
            
            width = ceil(size.width) + [UIScreen mainScreen].bounds.size.width/375*(10 + 5 + 13 + 10); // ceil 如果参数是小数，则求最小的证书但不小于本身
            height = ceil(size.height);
        }
        
        if (width > [UIScreen mainScreen].bounds.size.width/375*335) {
            width = [UIScreen mainScreen].bounds.size.width/375*335;
        }
    }
        
    return CGSizeMake(width, [UIScreen mainScreen].bounds.size.width/375*32);
    
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    // 水平上下
    return [UIScreen mainScreen].bounds.size.width/375*10;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    // 垂直左右
    return [UIScreen mainScreen].bounds.size.width/375*10;
}

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    // section 边界
    return UIEdgeInsetsMake([UIScreen mainScreen].bounds.size.width/375*5, [UIScreen mainScreen].bounds.size.width/375*15, [UIScreen mainScreen].bounds.size.width/375*5, [UIScreen mainScreen].bounds.size.width/375*15);
}

- (nonnull __kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    N_DictionaryPanelRecordCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([N_DictionaryPanelRecordCell class]) forIndexPath:indexPath];
    if (self.searchArray.count > 0) {
        cell.itemDic = self.searchArray[indexPath.row];
    }
    __weak typeof(self) weakSelf = self;
    cell.deleteAloneWordRecordBlock = ^(BOOL isDeleteWordRecord) {
        if (isDeleteWordRecord) {
            NSMutableArray *recordArr = [NSMutableArray arrayWithCapacity:0];
            recordArr = [weakSelf.searchArray mutableCopy];
            
            [recordArr removeObject:[NSString stringWithFormat:@"%@", weakSelf.searchArray[indexPath.row]]];
            weakSelf.searchArray = [recordArr copy];
            
            [[NSUserDefaults standardUserDefaults] setObject:weakSelf.searchArray forKey:@"dictionary"];
            [[NSUserDefaults standardUserDefaults] synchronize];
            
            [weakSelf.collectionView reloadData];
        }
    };
    
    return cell;
}

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    N_DictionaryPanelRecordCell *cell = (N_DictionaryPanelRecordCell *)[collectionView cellForItemAtIndexPath:indexPath];
    
    NSDictionary *dic = [self.searchArray objectAtIndex:indexPath.row];
    NSString *word = [NSString stringWithFormat:@"%@",[dic valueForKey:@"word"]];
    
    if ([word isChinese])
    {
        
    }
    else
    {

    }
}