iOS collectionView拖拽排序

项目中首页按钮按照需求需要实现拖拽排序并且记录排序后的布局，下次再进入APP后展示排序后的布局。

功能分析

实现此功能需要实现两个点，第一就是拖拽排序的实现，第二就是存储排序后的布局，针对第一个功能点，拖拽排序：这个可以使用collectionView系统自带的功能来实现，针对第二个功能点，我使用NSUserDefaults本地存储盛放collectionViewCell内容的数组。
整体效果如图：

屏幕快照 2019-01-29 上午11.10.24.png

本地存储的实现

每个cell由背景图片和title组成，NSDictionary *dic1 = @{@"title":@"标题", @"img":@"bgImg"};每个字典存放两个字段，根据需求，创建相应的字典，NSArray *tempArr = @[dic1,dic2,dic3,dic4,dic5]``[self.homeBtnsArr addObjectsFromArray:tempArr];将字典放在数组中，便于在collectionView的代理方法中使用，[[NSUserDefaults standardUserDefaults] setObject:self.homeBtnsArr forKey:@"stuHomeBtns"];将数组做本地储存，在每次进入界面时，先去NSUserDefaults中查找存放的数组，再去使用。

拖拽移动功能的实现

1、创建collectionView

UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    flowLayout.itemSize = CGSizeMake((SCREEN_WIDTH-50.0)/4, 85);
    flowLayout.minimumLineSpacing = 0.1;
    flowLayout.minimumInteritemSpacing = 0.1;
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:flowLayout];
    collectionView.backgroundColor = [UIColor whiteColor];
    collectionView.delegate = self;
    collectionView.dataSource = self;
    self.collectionView = collectionView;
    [self addSubview:collectionView];
    [collectionView makeConstraints:^(MASConstraintMaker *make) {
        make.edges.equalTo(0);
    }];
    [collectionView registerClass:[HomeSortBtnCell class] forCellWithReuseIdentifier:@"HomeSortBtnCell"];

2、在collectionView上添加长按手势

UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handlelongGesture:)];
    [collectionView addGestureRecognizer:longPress];

3、长按手势响应方法

#pragma mark 长按响应方法
- (void)handlelongGesture:(UILongPressGestureRecognizer *)longPress {
    [self action:longPress];
}

4、处理长按手势

- (void)action:longPress:(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;
                }
                HomeSortBtnCell *cell = (HomeSortBtnCell *)[self.collectionView cellForItemAtIndexPath:indexPath];
                [self bringSubviewToFront:cell];
                //iOS9 方法 移动cell
                [self.collectionView beginInteractiveMovementForItemAtIndexPath:indexPath];
            }
            break;
        case UIGestureRecognizerStateChanged:
            {
                //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:
            [self.collectionView cancelInteractiveMovement];
            break;
    }
}

这里处理长按手势的时候，（一）、判断手势开始，判断手势落点位置是否在collectionView的cell上，collectionView系统的方法：indexPathForItemAtPoint:这里的point为：[longPress locationInView:self.collectionView]，获取到手势落点的indexPath后，根据indexPath查找到相应位置的cell，然后[self bringSubviewToFront:cell];将cell提到前层展示，给人以悬浮的感觉，这时就开始了collectionView的移动操作：[self.collectionView beginInteractiveMovementForItemAtIndexPath:indexPath];。（二）、当手势在移动的过程中，collectionView随时更新cell的位置：[self.collectionView updateInteractiveMovementTargetPosition:[longPress locationInView:self.collectionView]];。（三）、手势结束后，collectionView也随之关闭cell的移动：[self.collectionView endInteractiveMovement];。

这里不仅仅需要处理手势事件，还需要遵循collectionView相关的代理方法：

//开启collectionView可以移动
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}

//处理collectionView移动过程中的数据操作
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath {
    //取出移动row 数据
    NSDictionary *dic = self.viewModel.homeBtnsArr[sourceIndexPath.row];
    //从数据源中移除该数据
    [self.viewModel.homeBtnsArr removeObject:dic];
    //将数据插入到数据源中目标位置
    [self.viewModel.homeBtnsArr insertObject:dic atIndex:destinationIndexPath.row];
    
    NSArray *tempBtns = [self.viewModel.homeBtnsArr copy];
    if ([self.viewModel fetchIsTeacherRole]) {
        //教师端
        [[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"teaHomeBtns"];
    } else {
        [[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"stuHomeBtns"];
    }
}

在- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath代理方法中，（一）、 //取出移动row 数据
NSDictionary dic = self.viewModel.homeBtnsArr[sourceIndexPath.row];（二）、//从数据源中移除该数据 [self.viewModel.homeBtnsArr removeObject:dic];（三）、//将数据插入到数据源中目标位置 [self.viewModel.homeBtnsArr insertObject:dic atIndex:destinationIndexPath.row];（四）、NSArray *tempBtns = [self.viewModel.homeBtnsArr copy];[[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"teaHomeBtns"];将改变后的cell内容数组存储到本地。

以上就是iOS9及以上移动collectionViewCell的方法，我们利用系统封装好的方法，相对比较容易的实现了功能。接下来看一下iOS9以下我们需要怎么实现

iOS9以下

#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;
                }
                HomeSortBtnCell *cell = (HomeSortBtnCell *)[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 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;
                }];
                
                //取出移动row 数据
//                NSDictionary *dic = self.viewModel.homeBtnsArr[self.oldIndexPath.row];
//                //从数据源中移除该数据
//                [self.viewModel.homeBtnsArr removeObject:dic];
                
            }
            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 (HomeSortBtnCell *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 = sqrt(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];
                       /*更新数据源 须在移动之前*/
                        //取出移动row 数据
                        NSDictionary *dic = self.viewModel.homeBtnsArr[self.oldIndexPath.row];
                        //从数据源中移除该数据
                        [self.viewModel.homeBtnsArr removeObject:dic];
                        //将数据插入到数据源中目标位置
                        [self.viewModel.homeBtnsArr insertObject:dic atIndex:self.moveIndexPath.row];
                        
                        //移动 会调用MoveToIndexPath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
                HomeSortBtnCell *cell = (HomeSortBtnCell *)[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;
                    
                    //本地存储已修改的按钮数组
                    NSArray *tempBtns = [self.viewModel.homeBtnsArr copy];
                    if ([self.viewModel fetchIsTeacherRole]) {
                        //教师端
                        [[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"teaHomeBtns"];
                    } else {
                        [[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"stuHomeBtns"];
                    }
                }];
            }
            break;
    }
}

iOS9以下就相对麻烦些了，首先在手势开始时，我们也同样需要找到手势落点所在位置的cell，然后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 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; }];
这里我们做这么多的操作，在iOS9及以上我们相应做的操作是：[self bringSubviewToFront:cell]; //iOS9 方法移动cell [self.collectionView beginInteractiveMovementForItemAtIndexPath:indexPath];。当手势发生改变，也就是我们开始移动的时候，截图的视图位置也随着手指移动而移动CGPoint currentPoint = [longPress locationInView:self.collectionView]; self.snapShotView.center = currentPoint;我们需要自己计算截图视图和哪个可见cell相交：for (HomeSortBtnCell *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 = sqrt(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]; /*更新数据源须在移动之前*/ //取出移动row 数据 NSDictionary *dic = self.viewModel.homeBtnsArr[self.oldIndexPath.row]; //从数据源中移除该数据 [self.viewModel.homeBtnsArr removeObject:dic]; //将数据插入到数据源中目标位置 [self.viewModel.homeBtnsArr insertObject:dic atIndex:self.moveIndexPath.row]; //移动会调用MoveToIndexPath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; } }
手势结束之后，我们需要将截图的视图隐藏移除，并且刷新当前视图布局：
//手势结束和其他状态 HomeSortBtnCell *cell = (HomeSortBtnCell *)[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; //本地存储已修改的按钮数组 NSArray *tempBtns = [self.viewModel.homeBtnsArr copy]; if ([self.viewModel fetchIsTeacherRole]) { //教师端 [[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"teaHomeBtns"]; } else { [[NSUserDefaults standardUserDefaults] setObject:tempBtns forKey:@"stuHomeBtns"]; } }];