gistfile1.m

@interface ATParallaxTableHeaderView : UIView

@property (weak, nonatomic, readonly) UIView *contentView;

- (id)initWithContentView:(UIView *)contentView;

- (void)attachToTableView:(UITableView *)tableView;

@end

gistfile2.m

#import "ATParallaxTableHeaderView.h"

static void *ATParallaxTableHeaderViewObserverContext = &ATParallaxTableHeaderViewObserverContext;

@interface ATParallaxTableHeaderView ()

@property (weak, nonatomic, readwrite) UIView *contentView;
@property (weak, nonatomic) UITableView *tableView;

@end

@implementation ATParallaxTableHeaderView

#pragma mark - Lifecycle

- (id)initWithContentView:(UIView *)contentView
{
    NSParameterAssert(contentView);

    if (!(self = [super initWithFrame:contentView.bounds])) {
        return nil;
    }

    [self addSubview:contentView];
    _contentView = contentView;

    return self;
}

- (void)dealloc
{
    [self removeObserver:self forKeyPath:self.observerKeyPath context:ATParallaxTableHeaderViewObserverContext];
}

#pragma mark - API

#pragma mark Hooking Onto the Table View

- (void)attachToTableView:(UITableView *)tableView
{
    NSParameterAssert(tableView);

    self.tableView = tableView;
    [self configureTableView];
    [self observeTableViewContentOffsetChanges];
}

- (void)configureTableView
{
    self.tableView.contentInset = UIEdgeInsetsMake(CGRectGetHeight(self.bounds), 0, 0, 0);
    [self.tableView addSubview:self];
}

#pragma mark Responding to Table View Content Offset Changes

- (void)observeTableViewContentOffsetChanges
{
    [self.tableView addObserver:self forKeyPath:self.observerKeyPath options:NSKeyValueObservingOptionNew context:ATParallaxTableHeaderViewObserverContext];
}

#pragma mark KVO

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if (context != ATParallaxTableHeaderViewObserverContext) {
        return;
    }

    CGPoint contentOffset = [change[NSKeyValueChangeNewKey] CGPointValue];

    if (contentOffset.y < -CGRectGetHeight(self.bounds)) {
        CGRect frame = self.contentView.frame;
        frame.origin.y = contentOffset.y;
        frame.size.height = -contentOffset.y;
        self.contentView.frame = frame;
    }
}

- (NSString *)observerKeyPath
{
    static NSString *observerKeyPath;

    if (!observerKeyPath) {
        observerKeyPath = NSStringFromSelector(@selector(contentOffset));
    }

    return observerKeyPath;
}

@end