manage scrollsToTop

gistfile1.m

#import "ScrollsToTopManager.h"

@interface ScrollsToTopManager()
@property (nonatomic) NSHashTable *scrollViews;
@end

@implementation ScrollsToTopManager

+ (instancetype)sharedManager
{
    static id instance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[self alloc] init];
    });
    return instance;
}

- (id)init
{
    self = [super init];
    if (self) {
        self.scrollViews = [NSHashTable weakObjectsHashTable];
    }
    return self;
}

- (void)registerScrollView:(UIScrollView *)scrollView
{
    [self.scrollViews addObject:scrollView];
}

- (void)becomeScrollsToTop:(UIScrollView *)scrollView
{
    if ([scrollView respondsToSelector:@selector(setScrollsToTop:)]) {
        scrollView.scrollsToTop = YES;
    }

    NSMutableSet *otherScrollViews = [[self.scrollViews setRepresentation] mutableCopy];
    [otherScrollViews minusSet:[NSSet setWithObject:scrollView]];

    for (UIScrollView *otherScrollView in otherScrollViews) {
        if ([otherScrollView respondsToSelector:@selector(setScrollsToTop:)]) {
            otherScrollView.scrollsToTop = NO;
        }
    }
}

@end