iOS - 将UICollectionViewCell滚动到菜单

我的是横向滑动的菜单，点击当前cell时，让其滚动到中间位置，注意要判断最左边和最右边的cell，点击时不能发生偏移，以下是我点击时的代码：

    UICollectionViewLayoutAttributes * att = [self.collectionView layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForRow:index inSection:0]];
    CGFloat width = self.collectionView.width;
    if(self.collectionView.contentSize.width > width) {
        if(att.frame.origin.x > width/2.f) {
    //        NSLog(@"%f ---- %f", width/2.f, self.collectionView.contentSize.width - att.frame.origin.x);
            if(self.collectionView.contentSize.width - att.frame.origin.x - att.bounds.size.width/2.f > width/2.f) {
                CGPoint point = CGPointMake(att.frame.origin.x - width/2.f + att.bounds.size.width/2.f , 0);
                [self.collectionView setContentOffset:point animated:YES];
            }else {
                [self.collectionView setContentOffset:CGPointMake(self.collectionView.contentSize.width - width, 0) animated:YES];
            }
        }else {
            [self.collectionView setContentOffset:CGPointMake(0, 0) animated:YES];
        }
    }

如果不采用UICollectionView制作菜单，用UIScrollView和UIButton制作，代码如下：

- (void)setUI {

    UIScrollView *topTitleSC = [[UIScrollView alloc] init];
    topTitleSC.showsHorizontalScrollIndicator = NO;
    topTitleSC.showsVerticalScrollIndicator = NO;
    [self.view addSubview:topTitleSC];
    self.titleSC = topTitleSC;
    [topTitleSC mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(self.view.mas_safeAreaLayoutGuideTop);
        make.left.equalTo(self.view.mas_safeAreaLayoutGuideLeft);
        make.right.equalTo(self.view.mas_safeAreaLayoutGuideRight);
        make.height.offset(scHeight);
    }];
    
    
    
    UIButton *selectBtn = nil;
    for (int i =0; i<self.titleArr.count; i++) {
         TYAVLableModel *model =  self.titleArr[i];
        UIButton *btn = [UIButton buttonWithTitle:model.name titleColor:main_light_text_color font:[UIFont systemFontOfSize:15] target:self action:@selector(titleBtnClick:)];
        btn.frame = CGRectMake((jianGe+btnWidth)*i+jianGe, 0, btnWidth, scHeight-1);
        btn.tag = i+100;
        [topTitleSC addSubview:btn];
        
        
        if (i == 0) {
            _lineLab = [[UILabel alloc] initWithFrame:CGRectMake(jianGe, scHeight-1, btnWidth, 1)];
            _lineLab.backgroundColor = main_select_text_color;
            [topTitleSC addSubview:_lineLab];
        }
       
        selectBtn = btn;
    }
    
    topTitleSC.contentSize = CGSizeMake(selectBtn.right+jianGe, topTitleSC.height);

    self.scrollView.contentSize = CGSizeMake(self.titleArr.count*KSCREEN_WIDTH, self.scrollView.height);
    
    [self addListVCWithIndex:0];
}

- (void)titleBtnClick:(UIButton *)btn {
    if(btn == _currentBtn) return;
    
    [_currentBtn setTitleColor:main_light_text_color forState:UIControlStateNormal];
    [btn setTitleColor:main_select_text_color forState:UIControlStateNormal];

    _lineLab.center = CGPointMake(btn.center.x, _lineLab.center.y);
    
    [UIView animateWithDuration:0.3 animations:^{
        [self.scrollView setContentOffset:CGPointMake((btn.tag-100)*KSCREEN_WIDTH, self.scrollView.contentOffset.y)  animated:NO];
    }];
    
    [self addListVCWithIndex:btn.tag-100];
    
    // 有数学公式得出的算法
    if((KSCREEN_WIDTH - btn.x) < 2*btn.width) {
        if((btn.x - (KSCREEN_WIDTH -btn.width)/2.f)<(self.titleSC.contentSize.width-KSCREEN_WIDTH)) {
            [UIView animateWithDuration:0.5 animations:^{
                self.titleSC.contentOffset = CGPointMake(btn.x - (KSCREEN_WIDTH -btn.width)/2.f, 0);
            }];
        } else {
            [UIView animateWithDuration:0.5 animations:^{
                self.titleSC.contentOffset = CGPointMake(self.titleSC.contentSize.width - KSCREEN_WIDTH, 0);
            }];
        }
    } else {
        [UIView animateWithDuration:0.5 animations:^{
            self.titleSC.contentOffset = CGPointMake(0, 0);
        }];
    }
    
    
    _currentBtn = btn;
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    
    NSInteger index = (scrollView.contentOffset.x+KSCREEN_WIDTH/2.f)/KSCREEN_WIDTH;
    UIButton *btn = (UIButton *)[self.titleSC viewWithTag:index+100];
    [self titleBtnClick:btn];
    
    [self addListVCWithIndex:(int)(scrollView.contentOffset.x/KSCREEN_WIDTH)];
}

#pragma mark - addVC

- (void)addListVCWithIndex:(NSInteger)index {
    
    if (index<0||index>=self.titleArr.count) {
        return;
    }
    //根据页数添加相对应的视图 并存入数组
    
    if (![_listVCQueue objectForKey:@(index)]) {
        TYAVHomeViewController *contentVC = [[TYAVHomeViewController alloc] init];
        [self addChildViewController:contentVC];
        TYAVLableModel *model =  self.titleArr[index];
        contentVC.vClass = model.name;

        contentVC.view.frame = CGRectMake(KSCREEN_WIDTH*index, 0, self.scrollView.width, self.scrollView.height);
        [self.scrollView addSubview:contentVC.view];
        
        [_listVCQueue setObject:contentVC forKey:@(index)];
    }
}