现在很多项目都会用到类似拖动的效果，比如今日头条和网易新闻之类的资讯类产品，都有用该技术设置模块顺序的操作。

在iOS9.0之后，苹果提供相关的方法，非常方便。

设定三个私有属性
@property(nonatomic,strong) NSMutableArray *arr;

@property(nonatomic,weak) UICollectionView *colView;

@property(nonatomic,strong) UILongPressGestureRecognizer *longPress;
//数据源
- (NSMutableArray *)arr{
    
    if (!_arr) {
        _arr = [NSMutableArray arrayWithObjects:@(1),@(2),@(3),@(4),@(5),@(6),@(7),@(8),@(9), nil];
    }
    return _arr;
}

1. 先创建UICollectionView

//创建布局对象
UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc]init];
//view
    UICollectionView *colView = [[UICollectionView alloc]initWithFrame:self.view.bounds collectionViewLayout:flowLayout];
//背景色
    colView.backgroundColor = [UIColor whiteColor];
    colView.delegate = self;
    colView.dataSource = self;
//控制布局
    colView.contentInset = UIEdgeInsetsMake(30, 20, 0, 20);
    CGFloat screenW = [UIScreen mainScreen].bounds.size.width;
    CGFloat space = 20;
    NSInteger col = 3;
    CGFloat itemSize = (screenW - (( col + 1 ) * space) - 6) / 3;
    
    flowLayout.itemSize = CGSizeMake(itemSize, itemSize);
    flowLayout.minimumInteritemSpacing = space;
    flowLayout.minimumLineSpacing = space;
    //添加长按手势
    _longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(longPressMoving:)];
    [colView addGestureRecognizer:_longPress];
    //属性连接
    self.colView = colView;
   //注册cell,记得先创建一个自定义cell
    [colView registerNib:[UINib nibWithNibName:@"MyCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"cell"];
    [self.view addSubview:colView];

--------------------------------------数据源方法---------------------------------------------

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

// The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    
    MyCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
    
    cell.num.text = [NSString stringWithFormat:@"%@",self.arr[indexPath.row]];
    
    return cell;
    
}

2.长按手势响应事件

- (void)longPressMoving:(UILongPressGestureRecognizer *)longPress{
//    筛选长按手势状态
    switch (_longPress.state) {
//            开始
        case UIGestureRecognizerStateBegan: {
            {
//手势作用的位置
                NSIndexPath *selectIndexPath = [self.colView indexPathForItemAtPoint:[_longPress locationInView:self.colView]];
                // 找到当前的cell
                MyCollectionViewCell *cell = (MyCollectionViewCell *)[self.colView cellForItemAtIndexPath:selectIndexPath];
//                拽起变大动画效果
                [UIView animateWithDuration:0.3 animations:^{
                    [cell setTransform:CGAffineTransformMakeScale(1.2, 1.2)];
                }];
               //开始移动
                [_colView beginInteractiveMovementForItemAtIndexPath:selectIndexPath];
            }
            break;
        }
        case UIGestureRecognizerStateChanged: {
//更新移动的位置
            [self.colView updateInteractiveMovementTargetPosition:[longPress locationInView:_longPress.view]];
            break;
        }
        case UIGestureRecognizerStateEnded: {
//结束移动
            [self.colView endInteractiveMovement];
            break;
        }
        default: [self.colView cancelInteractiveMovement];
            break;
    }
}

3.实现苹果官方的代理方法

- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath{
    return YES;
}

- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath{
    
    NSLog(@"%zd---%zd",sourceIndexPath.row,destinationIndexPath.row);
    NSIndexPath *selectIndexPath = [self.colView indexPathForItemAtPoint:[_longPress locationInView:self.colView]];
   //交换数据源的内容
    [self.arr exchangeObjectAtIndex:sourceIndexPath.item withObjectAtIndex:destinationIndexPath.item];
//    [self.colView reloadData];
    
    NSLog(@"%@",self.arr);
}

实现完以上的方法，可以快速构建一个可拖拽排序的cell界面。