A super-quick clone of Facebook Paper's springy table view

ABSpringDemoViewController.m

//
//  ABSpringDemoViewController.m
//  Springy
//

#import "ABSpringDemoViewController.h"

@interface ABSpringDemoViewController () <UITableViewDataSource, UITableViewDelegate> {
    UITableView *_tableView;
    CADisplayLink *_displayLink;
    UIPanGestureRecognizer *_panGestureRecognizer_;
    NSMutableArray *_objects;
    CGFloat _panOrigin;
    CGPoint _panPosition;
    CGPoint _panTranslation;
    BOOL _isDragging;
}
@end

@implementation ABSpringDemoViewController

- (void)loadView {
    _tableView = [[UITableView alloc] initWithFrame:CGRectZero];
    _tableView.delegate = self;
    _tableView.dataSource = self;
    self.view = _tableView;

    _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(onEnterFrame:)];
    [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    
    _objects = [NSMutableArray arrayWithArray:@[
        @"Red",
        @"Orange",
        @"Yellow",
        @"Green",
        @"Cyan",
        @"Blue",
        @"Violet",
        @"Purple",
        @"Magenta",
        @"Pink",
        @"White",
        @"Gray",
        @"Black",
    ]];
    
    _panGestureRecognizer_ = [[UIPanGestureRecognizer alloc] initWithTarget:self
                                                                     action:@selector(panGestureChanged:)];
    [self.view addGestureRecognizer:_panGestureRecognizer_];
}

- (void)onEnterFrame:(id)sender {
    if (!_isDragging) return;
    
    NSArray *visibleCells = [_tableView visibleCells];
    UIView *touchedCell = [self getCellForPosition:_panPosition];
    NSUInteger touchedCellIndex = [visibleCells indexOfObject:touchedCell];
    
    [self dragView:touchedCell withTarget:_panTranslation];
    
    for (NSInteger i = touchedCellIndex + 1; i < visibleCells.count; i++) {
        UITableViewCell *cell = [visibleCells objectAtIndex:i];
        UITableViewCell *target = [visibleCells objectAtIndex:i - 1];
        [self dragView:cell withTarget:target.frame.origin];
    }
    
    for (NSInteger i = touchedCellIndex - 1; i >= 0; i--) {
        UITableViewCell *cell = [visibleCells objectAtIndex:i];
        UITableViewCell *target = [visibleCells objectAtIndex:i + 1];
        [self dragView:cell withTarget:target.frame.origin];
    }
}

- (void)dragView:(UIView *)view withTarget:(CGPoint)target {
    CGFloat dx = (target.x - view.frame.origin.x) * 0.3;
    view.transform = CGAffineTransformTranslate(view.transform, dx, 0);
}

- (UITableViewCell *)getCellForPosition:(CGPoint)position {
    NSArray *visibleCells = [_tableView visibleCells];
    for (UITableViewCell *cell in visibleCells) {
        if (CGRectGetMaxY(cell.frame) > position.y) {
            return cell;
        }
    }
    return [visibleCells lastObject];
}

- (void)panGestureChanged:(UIPanGestureRecognizer *)gestureRecognizer {
    CGPoint translation = [gestureRecognizer translationInView:self.view];
    switch (gestureRecognizer.state) {
        case UIGestureRecognizerStateBegan:
            _panOrigin = translation.x;
            _isDragging = YES;
        
        case UIGestureRecognizerStateChanged:
            _panPosition = [gestureRecognizer locationInView:self.view];
            _panTranslation = [gestureRecognizer translationInView:self.view];
            break;

        case UIGestureRecognizerStateEnded: {
            [UIView animateWithDuration:0.4 animations:^{
                for (NSIndexPath *index in [_tableView indexPathsForVisibleRows]) {
                    UITableViewCell *cell = [_tableView cellForRowAtIndexPath:index];
                    CGRect frame = cell.frame;
                    frame.origin.x = 0;
                    cell.frame = frame;
                }
            }];
        }
            
        default:
            _isDragging = NO;
            break;
    }
}

#pragma mark - Table View

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return _objects.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"Cell"];
    }
    NSDate *object = _objects[indexPath.row];
    cell.textLabel.text = [object description];
    cell.selectionStyle = UITableViewCellSelectionStyleNone;
    return cell;
}

@end