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

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{
    CGPoint oldPoint = [change[@"old"] CGPointValue];
    CGPoint newPoint = [change[@"new"] CGPointValue];
//    NSLog(@"%@",change);
    CGFloat newY = newPoint.y;
    CGFloat oldY = oldPoint.y;
   if ( newY - oldY > 0) { //判断
        
        self.imageView.y -= newY;
        
        self.tableView.y = self.imageView.bottom;
        
        [self.tableView setContentOffset:CGPointMake(0, 0)];
     
    }
    else if (  newY - oldY < 0) {
//        self.imageView.y = self.imageView.y - newY;
//        if (self.imageView.y >= 0) {
//            self.imageView.y = 0;
//        }
//        self.tableView.y = self.imageView.bottom;
        self.imageView.y -= newY;
        
        self.tableView.y = self.imageView.bottom;
        
        [self.tableView setContentOffset:CGPointMake(0, 0)];

    }

}