iOS开发之多视图滑动点击切换实现

NSInteger  min = HYColumn  / 2 ;
if (_selectedIndex = self.titles.count - min) {
    UIButton * tempBtn = self.titles[self.titles.count - min - 1];
    CGFloat btnX = (HYColumn % 2 ) ? tempBtn.center.x : (tempBtn.center.x + btn.frame.size.width * 0.5) ;
    CGFloat offsetX = _tabbar.center.x - btnX;
    [UIView animateWithDuration:0.25 animations:^{
      _tabbar.contentOffset = CGPointMake(- offsetX, 0);
    }];    
}else if (_selectedIndex > min && _selectedIndex < self.titles.count - min && self.titles.count > HYColumn ) {
       CGFloat btnX  = (HYColumn % 2 ) ? btn.center.x : (btn.center.x - btn.frame.size.width * 0.5) ;
       CGFloat offsetX = _tabbar.center.x - btnX;
       [UIView animateWithDuration:0.25 animations:^{
         _tabbar.contentOffset = CGPointMake( - offsetX, 0);
           }];
    } else {
       [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}