iOS使用UICollectionView实现拖拽移动单元格

@interface ViewController ()<UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>
 
@property (nonatomic, strong) NSMutableArray *dataArr;
@property (nonatomic, strong) UICollectionView *collectionView;

@property (nonatomic, strong) NSIndexPath *oldIndexPath;

@property (nonatomic, strong) UIView *snapshotView;

@property (nonatomic, strong) NSIndexPath *moveIndexPath;
 
@end

CGFloat SCREEN_WIDTH = self.view.frame.size.width;
    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    flowLayout.itemSize = CGSizeMake((SCREEN_WIDTH-40.0)/3, (SCREEN_WIDTH-40.0)/3);
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 50.0, SCREEN_WIDTH, (SCREEN_WIDTH-40.0)/3+20.0) collectionViewLayout:flowLayout];
    collectionView.dataSource = self;
    collectionView.delegate = self;
    collectionView.backgroundColor = [UIColor whiteColor];
    [collectionView reGISterClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"uicollectionviewcell"];
    [self.view addSubview:self.collectionView = collectionView];
    
    // 添加长按手势
    UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handlelongGesture:)];
    [collectionView addGestureRecognizer:longPress];

self.dataArr = [[NSMutableArray alloc] init];
for (NSInteger index = 0; index < 50; index ++) {
        CGFloat hue = (arc4random()%256/256.0); //0.0 到 1.0
        CGFloat saturation = (arc4random()%128/256.0)+0.5; //0.5 到 1.0
        CGFloat brightness = (arc4random()%128/256.0)+0.5; //0.5 到 1.0
        UIColor *color = [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:0.5];
        [self.dataArr addObject:color];
    }

#pragma mark - UICollectionViewDataSource
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return self.dataArr.count;
}
 
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"uicollectionviewcell" forIndexPath:indexPath];
    cell.backgroundColor = self.dataArr[indexPath.row];
    return cell;
}

#pragma mark - 长按手势
- (void)handlelongGesture:(UILongPressGestureRecognizer *)longPress
{
    if ([[[UIDevice currentDevice] systemVersion] floatValue] < 9.0) {
        [self action:longPress];
    } else {
        [self iOS9_Action:longPress];
    }
}

#pragma mark - iOS9 之后的方法
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath
{
    // 返回YES允许row移动
    return YES;
}
 
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath
{
    //取出移动row数据
    id color = self.dataArr[sourceIndexPath.row];
    //从数据源中移除该数据
    [self.dataArr removeObject:color];
    //将数据插入到数据源中的目标位置
    [self.dataArr insertObject:color atIndex:destinationIndexPath.row];
}
 
- (void)iOS9_Action:(UILongPressGestureRecognizer *)longPress
{
    switch (longPress.state) {
        case UIGestureRecognizerStateBegan:
        { //手势开始
            //判断手势落点位置是否在row上
            NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:[longPress locationInView:self.collectionView]];
            if (indexPath == nil) {
                break;
            }
            UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:indexPath];
            [self.view bringSubviewToFront:cell];
            //iOS9方法 移动cell
            [self.collectionView beginInteractiveMovementForItemAtIndexPath:indexPath];
        }
            break;
        case UIGestureRecognizerStateChanged:
        { // 手势改变
            // iOS9方法 移动过程中随时更新cell位置
            [self.collectionView updateInteractiveMovementTargetPosition:[longPress locationInView:self.collectionView]];
        }
            break;
        case UIGestureRecognizerStateEnded:
        { // 手势结束
            // iOS9方法 移动结束后关闭cell移动
            [self.collectionView endInteractiveMovement];
        }
            break;
        default: //手势其他状态
            [self.collectionView cancelInteractiveMovement];
            break;
    }
}

#pragma mark - iOS9 之前的方法
- (void)action:(UILongPressGestureRecognizer *)longPress
{
    switch (longPress.state) {
        case UIGestureRecognizerStateBegan:
        { // 手势开始
            //判断手势落点位置是否在row上
            NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:[longPress locationInView:self.collectionView]];
            self.oldIndexPath = indexPath;
            if (indexPath == nil) {
                break;
            }
            UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:indexPath];
            // 使用系统的截图功能,得到cell的截图视图
            UIView *snapshotView = [cell snapshotViewAfterScreenUpdates:NO];
            snapshotView.frame = cell.frame;
            [self.view addSubview:self.snapshotView = snapshotView];
            // 截图后隐藏当前cell
            cell.hidden = YES;
            
            CGPoint currentPoint = [longPress locationInView:self.collectionView];
            [UIView animateWithDuration:0.25 animations:^{
                snapshotView.transfORM = CGAffineTransformMakeScale(1.05, 1.05);
                snapshotView.center = currentPoint;
            }];
        }
            break;
        case UIGestureRecognizerStateChanged:
        { // 手势改变
            //当前手指位置 截图视图位置随着手指移动而移动
            CGPoint currentPoint = [longPress locationInView:self.collectionView];
            self.snapshotView.center = currentPoint;
            // 计算截图视图和哪个可见cell相交
            for (UICollectionViewCell *cell in self.collectionView.visibleCells) {
                // 当前隐藏的cell就不需要交换了,直接continue
                if ([self.collectionView indexPathForCell:cell] == self.oldIndexPath) {
                    continue;
                }
                // 计算中心距
                CGFloat space = sqrtf(pow(self.snapshotView.center.x - cell.center.x, 2) + powf(self.snapshotView.center.y - cell.center.y, 2));
                // 如果相交一半就移动
                if (space <= self.snapshotView.bounds.size.width / 2) {
                    self.moveIndexPath = [self.collectionView indexPathForCell:cell];
                    //移动 会调用willMoveToIndexPath方法更新数据源
                    [self.collectionView moveItemAtIndexPath:self.oldIndexPath toIndexPath:self.moveIndexPath];
                    //设置移动后的起始indexPath
                    self.oldIndexPath = self.moveIndexPath;
                    break;
                }
            }
        }
            break;
        default:
        { // 手势结束和其他状态
            UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:self.oldIndexPath];
            // 结束动画过程中停止交互,防止出问题
            self.collectionView.userInteractionEnabled = NO;
            // 给截图视图一个动画移动到隐藏cell的新位置
            [UIView animateWithDuration:0.25 animations:^{
                self.snapshotView.center = cell.center;
                self.snapshotView.transform = CGAffineTransformMakeScale(1.0, 1.0);
            } completion:^(BOOL finished) {
                // 移除截图视图,显示隐藏的cell并开始交互
                [self.snapshotView removeFromSuperview];
                cell.hidden = NO;
                self.collectionView.userInteractionEnabled = YES;
            }];
        }
            break;
    }
}

// Support for reordering
- (BOOL)beginInteractiveMovementForItemAtIndexPath:(NSIndexPath *)indexPath NS_AVaiLABLE_IOS(9_0); // returns NO if reordering was prevented from beginning - otherwise YES
- (void)updateInteractiveMovementTargetPosition:(CGPoint)targetPosition NS_AVAILABLE_IOS(9_0);
- (void)endInteractiveMovement NS_AVAILABLE_IOS(9_0);
- (void)cancelInteractiveMovement NS_AVAILABLE_IOS(9_0);