【推荐】iOS集合视图的可重新排序的layout

　　在实际项目中你或许会遇到在一个集合视图中移动一项到另外一个位置，那么此时我们需要对视图中的元素进行重新排序，今天推荐一个很好用的第三方类LXReorderableCollectionViewFlowLayout【点此链接进入GITHUB】

下面附上实现代码

//
//  LXReorderableCollectionViewFlowLayout.h
//
//  Created by Stan Chang Khin Boon on 1/10/12.
//  Copyright (c) 2012 d--buzz. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface LXReorderableCollectionViewFlowLayout : UICollectionViewFlowLayout <UIGestureRecognizerDelegate>

@property (assign, nonatomic) CGFloat scrollingSpeed;
@property (assign, nonatomic) UIEdgeInsets scrollingTriggerEdgeInsets;
@property (strong, nonatomic, readonly) UILongPressGestureRecognizer *longPressGestureRecognizer;
@property (strong, nonatomic, readonly) UIPanGestureRecognizer *panGestureRecognizer;

- (void)setUpGestureRecognizersOnCollectionView __attribute__((deprecated("Calls to setUpGestureRecognizersOnCollectionView method are not longer needed as setup are done automatically through KVO.")));

@end

@protocol LXReorderableCollectionViewDataSource <UICollectionViewDataSource>

@optional

- (void)collectionView:(UICollectionView *)collectionView itemAtIndexPath:(NSIndexPath *)fromIndexPath willMoveToIndexPath:(NSIndexPath *)toIndexPath;
- (void)collectionView:(UICollectionView *)collectionView itemAtIndexPath:(NSIndexPath *)fromIndexPath didMoveToIndexPath:(NSIndexPath *)toIndexPath;

- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath;
- (BOOL)collectionView:(UICollectionView *)collectionView itemAtIndexPath:(NSIndexPath *)fromIndexPath canMoveToIndexPath:(NSIndexPath *)toIndexPath;

@end

@protocol LXReorderableCollectionViewDelegateFlowLayout <UICollectionViewDelegateFlowLayout>
@optional

- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout willBeginDraggingItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout didBeginDraggingItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout willEndDraggingItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout didEndDraggingItemAtIndexPath:(NSIndexPath *)indexPath;

@end

LXReorderableCollectionViewFlowLayout.h

//
//  LXReorderableCollectionViewFlowLayout.m
//
//  Created by Stan Chang Khin Boon on 1/10/12.
//  Copyright (c) 2012 d--buzz. All rights reserved.
//

#import "LXReorderableCollectionViewFlowLayout.h"
#import <QuartzCore/QuartzCore.h>
#import <objc/runtime.h>

#define LX_FRAMES_PER_SECOND 60.0

#ifndef CGGEOMETRY_LXSUPPORT_H_
CG_INLINE CGPoint
LXS_CGPointAdd(CGPoint point1, CGPoint point2) {
    return CGPointMake(point1.x + point2.x, point1.y + point2.y);
}
#endif

typedef NS_ENUM(NSInteger, LXScrollingDirection) {
    LXScrollingDirectionUnknown = ,
    LXScrollingDirectionUp,
    LXScrollingDirectionDown,
    LXScrollingDirectionLeft,
    LXScrollingDirectionRight
};

static NSString * const kLXScrollingDirectionKey = @"LXScrollingDirection";
static NSString * const kLXCollectionViewKeyPath = @"collectionView";

@interface CADisplayLink (LX_userInfo)
@property (nonatomic, copy) NSDictionary *LX_userInfo;
@end

@implementation CADisplayLink (LX_userInfo)
- (void) setLX_userInfo:(NSDictionary *) LX_userInfo {
    objc_setAssociatedObject(self, "LX_userInfo", LX_userInfo, OBJC_ASSOCIATION_COPY);
}

- (NSDictionary *) LX_userInfo {
    return objc_getAssociatedObject(self, "LX_userInfo");
}
@end

@interface UICollectionViewCell (LXReorderableCollectionViewFlowLayout)

- (UIImage *)LX_rasterizedImage;

@end

@implementation UICollectionViewCell (LXReorderableCollectionViewFlowLayout)

- (UIImage *)LX_rasterizedImage {
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, self.isOpaque, 0.0f);
    [self.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

@end

@interface LXReorderableCollectionViewFlowLayout ()

@property (strong, nonatomic) NSIndexPath *selectedItemIndexPath;
@property (strong, nonatomic) UIView *currentView;
@property (assign, nonatomic) CGPoint currentViewCenter;
@property (assign, nonatomic) CGPoint panTranslationInCollectionView;
@property (strong, nonatomic) CADisplayLink *displayLink;

@property (assign, nonatomic, readonly) id<LXReorderableCollectionViewDataSource> dataSource;
@property (assign, nonatomic, readonly) id<LXReorderableCollectionViewDelegateFlowLayout> delegate;

@end

@implementation LXReorderableCollectionViewFlowLayout

- (void)setDefaults {
    _scrollingSpeed = 300.0f;
    _scrollingTriggerEdgeInsets = UIEdgeInsetsMake(50.0f, 50.0f, 50.0f, 50.0f);
}

- (void)setupCollectionView {
    _longPressGestureRecognizer = [[UILongPressGestureRecognizer alloc] initWithTarget:self
                                                                                action:@selector(handleLongPressGesture:)];
    _longPressGestureRecognizer.delegate = self;

    // Links the default long press gesture recognizer to the custom long press gesture recognizer we are creating now
    // by enforcing failure dependency so that they doesn't clash.
    for (UIGestureRecognizer *gestureRecognizer in self.collectionView.gestureRecognizers) {
        if ([gestureRecognizer isKindOfClass:[UILongPressGestureRecognizer class]]) {
            [gestureRecognizer requireGestureRecognizerToFail:_longPressGestureRecognizer];
        }
    }

    [self.collectionView addGestureRecognizer:_longPressGestureRecognizer];

    _panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self
                                                                    action:@selector(handlePanGesture:)];
    _panGestureRecognizer.delegate = self;
    [self.collectionView addGestureRecognizer:_panGestureRecognizer];

    // Useful in multiple scenarios: one common scenario being when the Notification Center drawer is pulled down
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleApplicationWillResignActive:) name: UIApplicationWillResignActiveNotification object:nil];
}

- (id)init {
    self = [super init];
    if (self) {
        [self setDefaults];
        [self addObserver:self forKeyPath:kLXCollectionViewKeyPath options:NSKeyValueObservingOptionNew context:nil];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if (self) {
        [self setDefaults];
        [self addObserver:self forKeyPath:kLXCollectionViewKeyPath options:NSKeyValueObservingOptionNew context:nil];
    }
    return self;
}

- (void)dealloc {
    [self invalidatesScrollTimer];
    [self removeObserver:self forKeyPath:kLXCollectionViewKeyPath];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillResignActiveNotification object:nil];
}

- (void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes {
    if ([layoutAttributes.indexPath isEqual:self.selectedItemIndexPath]) {
        layoutAttributes.hidden = YES;
    }
}

- (id<LXReorderableCollectionViewDataSource>)dataSource {
    return (id<LXReorderableCollectionViewDataSource>)self.collectionView.dataSource;
}

- (id<LXReorderableCollectionViewDelegateFlowLayout>)delegate {
    return (id<LXReorderableCollectionViewDelegateFlowLayout>)self.collectionView.delegate;
}

- (void)invalidateLayoutIfNecessary {
    NSIndexPath *newIndexPath = [self.collectionView indexPathForItemAtPoint:self.currentView.center];
    NSIndexPath *previousIndexPath = self.selectedItemIndexPath;

    if ((newIndexPath == nil) || [newIndexPath isEqual:previousIndexPath]) {
        return;
    }

    if ([self.dataSource respondsToSelector:@selector(collectionView:itemAtIndexPath:canMoveToIndexPath:)] &&
        ![self.dataSource collectionView:self.collectionView itemAtIndexPath:previousIndexPath canMoveToIndexPath:newIndexPath]) {
        return;
    }

    self.selectedItemIndexPath = newIndexPath;

    if ([self.dataSource respondsToSelector:@selector(collectionView:itemAtIndexPath:willMoveToIndexPath:)]) {
        [self.dataSource collectionView:self.collectionView itemAtIndexPath:previousIndexPath willMoveToIndexPath:newIndexPath];
    }

    __weak typeof(self) weakSelf = self;
    [self.collectionView performBatchUpdates:^{
        __strong typeof(self) strongSelf = weakSelf;
        if (strongSelf) {
            [strongSelf.collectionView deleteItemsAtIndexPaths:@[ previousIndexPath ]];
            [strongSelf.collectionView insertItemsAtIndexPaths:@[ newIndexPath ]];
        }
    } completion:^(BOOL finished) {
        __strong typeof(self) strongSelf = weakSelf;
        if ([strongSelf.dataSource respondsToSelector:@selector(collectionView:itemAtIndexPath:didMoveToIndexPath:)]) {
            [strongSelf.dataSource collectionView:strongSelf.collectionView itemAtIndexPath:previousIndexPath didMoveToIndexPath:newIndexPath];
        }
    }];
}

- (void)invalidatesScrollTimer {
    if (!self.displayLink.paused) {
        [self.displayLink invalidate];
    }
    self.displayLink = nil;
}

- (void)setupScrollTimerInDirection:(LXScrollingDirection)direction {
    if (!self.displayLink.paused) {
        LXScrollingDirection oldDirection = [self.displayLink.LX_userInfo[kLXScrollingDirectionKey] integerValue];

        if (direction == oldDirection) {
            return;
        }
    }

    [self invalidatesScrollTimer];

    self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(handleScroll:)];
    self.displayLink.LX_userInfo = @{ kLXScrollingDirectionKey : @(direction) };

    [self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
}

#pragma mark - Target/Action methods

// Tight loop, allocate memory sparely, even if they are stack allocation.
- (void)handleScroll:(CADisplayLink *)displayLink {
    LXScrollingDirection direction = (LXScrollingDirection)[displayLink.LX_userInfo[kLXScrollingDirectionKey] integerValue];
    if (direction == LXScrollingDirectionUnknown) {
        return;
    }

    CGSize frameSize = self.collectionView.bounds.size;
    CGSize contentSize = self.collectionView.contentSize;
    CGPoint contentOffset = self.collectionView.contentOffset;
    UIEdgeInsets contentInset = self.collectionView.contentInset;
    // Important to have an integer `distance` as the `contentOffset` property automatically gets rounded
    // and it would diverge from the view's center resulting in a "cell is slipping away under finger"-bug.
    CGFloat distance = rint(self.scrollingSpeed / LX_FRAMES_PER_SECOND);
    CGPoint translation = CGPointZero;

    switch(direction) {
        case LXScrollingDirectionUp: {
            distance = -distance;
            CGFloat minY = 0.0f - contentInset.top;

            if ((contentOffset.y + distance) <= minY) {
                distance = -contentOffset.y - contentInset.top;
            }

            translation = CGPointMake(0.0f, distance);
        } break;
        case LXScrollingDirectionDown: {
            CGFloat maxY = MAX(contentSize.height, frameSize.height) - frameSize.height + contentInset.bottom;

            if ((contentOffset.y + distance) >= maxY) {
                distance = maxY - contentOffset.y;
            }

            translation = CGPointMake(0.0f, distance);
        } break;
        case LXScrollingDirectionLeft: {
            distance = -distance;
            CGFloat minX = 0.0f - contentInset.left;

            if ((contentOffset.x + distance) <= minX) {
                distance = -contentOffset.x - contentInset.left;
            }

            translation = CGPointMake(distance, 0.0f);
        } break;
        case LXScrollingDirectionRight: {
            CGFloat maxX = MAX(contentSize.width, frameSize.width) - frameSize.width + contentInset.right;

            if ((contentOffset.x + distance) >= maxX) {
                distance = maxX - contentOffset.x;
            }

            translation = CGPointMake(distance, 0.0f);
        } break;
        default: {
            // Do nothing...
        } break;
    }

    self.currentViewCenter = LXS_CGPointAdd(self.currentViewCenter, translation);
    self.currentView.center = LXS_CGPointAdd(self.currentViewCenter, self.panTranslationInCollectionView);
    self.collectionView.contentOffset = LXS_CGPointAdd(contentOffset, translation);
}

- (void)handleLongPressGesture:(UILongPressGestureRecognizer *)gestureRecognizer {
    switch(gestureRecognizer.state) {
        case UIGestureRecognizerStateBegan: {
            NSIndexPath *currentIndexPath = [self.collectionView indexPathForItemAtPoint:[gestureRecognizer locationInView:self.collectionView]];

            if ([self.dataSource respondsToSelector:@selector(collectionView:canMoveItemAtIndexPath:)] &&
               ![self.dataSource collectionView:self.collectionView canMoveItemAtIndexPath:currentIndexPath]) {
                return;
            }

            self.selectedItemIndexPath = currentIndexPath;

            if ([self.delegate respondsToSelector:@selector(collectionView:layout:willBeginDraggingItemAtIndexPath:)]) {
                [self.delegate collectionView:self.collectionView layout:self willBeginDraggingItemAtIndexPath:self.selectedItemIndexPath];
            }

            UICollectionViewCell *collectionViewCell = [self.collectionView cellForItemAtIndexPath:self.selectedItemIndexPath];

            self.currentView = [[UIView alloc] initWithFrame:collectionViewCell.frame];

            collectionViewCell.highlighted = YES;
            UIImageView *highlightedImageView = [[UIImageView alloc] initWithImage:[collectionViewCell LX_rasterizedImage]];
            highlightedImageView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
            highlightedImageView.alpha = 1.0f;

            collectionViewCell.highlighted = NO;
            UIImageView *imageView = [[UIImageView alloc] initWithImage:[collectionViewCell LX_rasterizedImage]];
            imageView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
            imageView.alpha = 0.0f;

            [self.currentView addSubview:imageView];
            [self.currentView addSubview:highlightedImageView];
            [self.collectionView addSubview:self.currentView];

            self.currentViewCenter = self.currentView.center;

            __weak typeof(self) weakSelf = self;
            [UIView
             animateWithDuration:0.3
             delay:0.0
             options:UIViewAnimationOptionBeginFromCurrentState
             animations:^{
                 __strong typeof(self) strongSelf = weakSelf;
                 if (strongSelf) {
                     strongSelf.currentView.transform = CGAffineTransformMakeScale(1.1f, 1.1f);
                     highlightedImageView.alpha = 0.0f;
                     imageView.alpha = 1.0f;
                 }
             }
             completion:^(BOOL finished) {
                 __strong typeof(self) strongSelf = weakSelf;
                 if (strongSelf) {
                     [highlightedImageView removeFromSuperview];

                     if ([strongSelf.delegate respondsToSelector:@selector(collectionView:layout:didBeginDraggingItemAtIndexPath:)]) {
                         [strongSelf.delegate collectionView:strongSelf.collectionView layout:strongSelf didBeginDraggingItemAtIndexPath:strongSelf.selectedItemIndexPath];
                     }
                 }
             }];

            [self invalidateLayout];
        } break;
        case UIGestureRecognizerStateCancelled:
        case UIGestureRecognizerStateEnded: {
            NSIndexPath *currentIndexPath = self.selectedItemIndexPath;

            if (currentIndexPath) {
                if ([self.delegate respondsToSelector:@selector(collectionView:layout:willEndDraggingItemAtIndexPath:)]) {
                    [self.delegate collectionView:self.collectionView layout:self willEndDraggingItemAtIndexPath:currentIndexPath];
                }

                self.selectedItemIndexPath = nil;
                self.currentViewCenter = CGPointZero;

                UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForItemAtIndexPath:currentIndexPath];

                __weak typeof(self) weakSelf = self;
                [UIView
                 animateWithDuration:0.3
                 delay:0.0
                 options:UIViewAnimationOptionBeginFromCurrentState
                 animations:^{
                     __strong typeof(self) strongSelf = weakSelf;
                     if (strongSelf) {
                         strongSelf.currentView.transform = CGAffineTransformMakeScale(1.0f, 1.0f);
                         strongSelf.currentView.center = layoutAttributes.center;
                     }
                 }
                 completion:^(BOOL finished) {
                     __strong typeof(self) strongSelf = weakSelf;
                     if (strongSelf) {
                         [strongSelf.currentView removeFromSuperview];
                         strongSelf.currentView = nil;
                         [strongSelf invalidateLayout];

                         if ([strongSelf.delegate respondsToSelector:@selector(collectionView:layout:didEndDraggingItemAtIndexPath:)]) {
                             [strongSelf.delegate collectionView:strongSelf.collectionView layout:strongSelf didEndDraggingItemAtIndexPath:currentIndexPath];
                         }
                     }
                 }];
            }
        } break;

        default: break;
    }
}

- (void)handlePanGesture:(UIPanGestureRecognizer *)gestureRecognizer {
    switch (gestureRecognizer.state) {
        case UIGestureRecognizerStateBegan:
        case UIGestureRecognizerStateChanged: {
            self.panTranslationInCollectionView = [gestureRecognizer translationInView:self.collectionView];
            CGPoint viewCenter = self.currentView.center = LXS_CGPointAdd(self.currentViewCenter, self.panTranslationInCollectionView);

            [self invalidateLayoutIfNecessary];

            switch (self.scrollDirection) {
                case UICollectionViewScrollDirectionVertical: {
                    if (viewCenter.y < (CGRectGetMinY(self.collectionView.bounds) + self.scrollingTriggerEdgeInsets.top)) {
                        [self setupScrollTimerInDirection:LXScrollingDirectionUp];
                    } else {
                        if (viewCenter.y > (CGRectGetMaxY(self.collectionView.bounds) - self.scrollingTriggerEdgeInsets.bottom)) {
                            [self setupScrollTimerInDirection:LXScrollingDirectionDown];
                        } else {
                            [self invalidatesScrollTimer];
                        }
                    }
                } break;
                case UICollectionViewScrollDirectionHorizontal: {
                    if (viewCenter.x < (CGRectGetMinX(self.collectionView.bounds) + self.scrollingTriggerEdgeInsets.left)) {
                        [self setupScrollTimerInDirection:LXScrollingDirectionLeft];
                    } else {
                        if (viewCenter.x > (CGRectGetMaxX(self.collectionView.bounds) - self.scrollingTriggerEdgeInsets.right)) {
                            [self setupScrollTimerInDirection:LXScrollingDirectionRight];
                        } else {
                            [self invalidatesScrollTimer];
                        }
                    }
                } break;
            }
        } break;
        case UIGestureRecognizerStateCancelled:
        case UIGestureRecognizerStateEnded: {
            [self invalidatesScrollTimer];
        } break;
        default: {
            // Do nothing...
        } break;
    }
}

#pragma mark - UICollectionViewLayout overridden methods

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
    NSArray *layoutAttributesForElementsInRect = [super layoutAttributesForElementsInRect:rect];

    for (UICollectionViewLayoutAttributes *layoutAttributes in layoutAttributesForElementsInRect) {
        switch (layoutAttributes.representedElementCategory) {
            case UICollectionElementCategoryCell: {
                [self applyLayoutAttributes:layoutAttributes];
            } break;
            default: {
                // Do nothing...
            } break;
        }
    }

    return layoutAttributesForElementsInRect;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewLayoutAttributes *layoutAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];

    switch (layoutAttributes.representedElementCategory) {
        case UICollectionElementCategoryCell: {
            [self applyLayoutAttributes:layoutAttributes];
        } break;
        default: {
            // Do nothing...
        } break;
    }

    return layoutAttributes;
}

#pragma mark - UIGestureRecognizerDelegate methods

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer {
    if ([self.panGestureRecognizer isEqual:gestureRecognizer]) {
        return (self.selectedItemIndexPath != nil);
    }
    return YES;
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    if ([self.longPressGestureRecognizer isEqual:gestureRecognizer]) {
        return [self.panGestureRecognizer isEqual:otherGestureRecognizer];
    }

    if ([self.panGestureRecognizer isEqual:gestureRecognizer]) {
        return [self.longPressGestureRecognizer isEqual:otherGestureRecognizer];
    }

    return NO;
}

#pragma mark - Key-Value Observing methods

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:kLXCollectionViewKeyPath]) {
        if (self.collectionView != nil) {
            [self setupCollectionView];
        } else {
            [self invalidatesScrollTimer];
        }
    }
}

#pragma mark - Notifications

- (void)handleApplicationWillResignActive:(NSNotification *)notification {
    self.panGestureRecognizer.enabled = NO;
    self.panGestureRecognizer.enabled = YES;
}

#pragma mark - Depreciated methods

#pragma mark Starting from 0.1.0
- (void)setUpGestureRecognizersOnCollectionView {
    // Do nothing...
}

@end

LXReorderableCollectionViewFlowLayout.m

效果