UITableView和UIScrollView滚动方向的判断

1、首先为UITableView添加观察者

[tableView addObserver: self forKeyPath: @"contentOffset" options: NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context: nil];

2、在KVO中，根据UITableView对象的相关属性，完成UITableView滚动方向的判断

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([object isKindOfClass: [UITableView class]]) {
        CGPoint newPoint = [change[@"new"] CGPointValue];
        CGPoint oldPoint = [change[@"old"] CGPointValue];
        CGFloat newPointY = newPoint.y;
        CGFloat oldPointY = oldPoint.y;
        CGFloat frameHeight = ((UITableView *)object).frame.size.height;
        CGFloat contentSizeHeight = ((UITableView *)object).contentSize.height;

        //  这个地方把contentSizeHeight强制转为long类型很重要，因为本身它是CGFloat类型，所以可能会带有浮点数
        // 一般我们在做表格的时候，实际上正数居多，为什么用long而不是int，主要是表示的整数范围会更大
        if ((newPointY < oldPointY && (frameHeight + newPointY) < (long)contentSizeHeight) || newPointY < 0 || oldPointY < 0) {
            if (newPointY <= 0 || oldPointY <= 0) {
                NSLog(@"top");
            } else {
                NSLog(@"scroll down");
            }
        } else if (newPointY > oldPointY) {
            if ((frameHeight + newPointY >= contentSizeHeight)) {
                NSLog(@"bottom");
            } else {
                NSLog(@"scroll up");
            }
        }
    }
}