1.创建工程项目和视图控制器,如下图

2.声明对象和设置代理和数据源代理

@interface ViewController ()@property (nonatomic, strong) NSMutableArray *dataArr;@property (nonatomic, strong) UICollectionView *collectionView;/**之前选中cell的NSIndexPath*/@property (nonatomic, strong) NSIndexPath *oldIndexPath;/**单元格的截图*/@property (nonatomic, strong) UIView *snapshotView;/**之前选中cell的NSIndexPath*/@property (nonatomic, strong) NSIndexPath *moveIndexPath;@end

3.初始化UICollectionView,并添加长按手势,在viewDidLoad中初始化

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];

4.实例化数据源,(50个随机颜色,透明度0.8),在viewDidLoad中初始化

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];  }

5.实现UICollectionView的UICollectionViewDataSource的两个必须实现的方法

#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;}

6.重点来了,实现长按手势方法

#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];  }}

7.iOS9之后的实现

#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;  }}

8.iOS9之前的实现

#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;  }}

三.iOS9之后添加的API如下

// 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);