collectionView 拖动

##collectionView 拖动代理的变化

#####附上一demo 仿支付宝: https://github.com/ongfei/SortModule

####iOS9 之后 collectionView 新增拖动代理

// 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);

#####9之后的处理

#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;  
    }  
}  

#####9之前的处理

#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;  
    }  
}