- (void)viewDidLoad
{
 [super viewDidLoad];
 // Do any additional setup after loading the view.
 [self createTitleScrollView];
 [self createButtonLine];
 [self createContentScrollview];
}
 
#pragma mark - 初始化UI
- (void)createTitleScrollView
{
 // 根据是否有导航栏调整坐标
 CGFloat marginY = self.navigationController ? self.navigationController.view.frame.size.height : kUpMargin;
 
 // 标题栏,包括小横线的位置
 _titleScrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, marginY, kFrameWidth, kTitleHeight + kButtonLineHeight)];
 _titleScrollView.showsHorizontalScrollIndicator = NO;
 _titleScrollView.bounces = NO;
 _titleScrollView.delegate = self;
 [self.view addSubview:_titleScrollView];
 
 // 添加button
 NSArray *titleArray = @[@"头条", @"社会", @"财经", @"科技", @"体育", @"娱乐", @"时尚", @"军事", @"教育", @"游戏"];
 _pageCount = titleArray.count;
 _titleScrollView.contentSize = CGSizeMake(kButtonWidth * _pageCount, kTitleHeight);
 for (int i = 0; i < _pageCount; i++)
 {
  UIButton *titleBtn = [[UIButton alloc] initWithFrame:CGRectMake(kButtonWidth * i, 0, kButtonWidth, kTitleHeight)];
  [titleBtn setTitle:titleArray[i] forState:UIControlStateNormal];
  [titleBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  titleBtn.titleLabel.font = [UIFont systemFontOfSize:16];
  [titleBtn addTarget:self action:@selector(titleButtonClicked:) forControlEvents:UIControlEventTouchDown];
  titleBtn.tag = 1000 + i; // button做标记，方便后面索引，为了不出冲突，就把这个数值设得大一些
  [_titleScrollView addSubview:titleBtn];
 };
}
 
- (void)createButtonLine
{
 // 初始时刻停在最左边与按钮对齐
 _buttonLine = [[UIView alloc] initWithFrame:CGRectMake(0, kTitleHeight, kButtonWidth, kButtonLineHeight)];
 _buttonLine.backgroundColor = [UIColor redColor];
 // 小横线加载scrollview上才能跟随button联动
 [_titleScrollView addSubview:_buttonLine];
}
 
- (void)createContentScrollview
{
 CGFloat marginY = self.navigationController ? self.navigationController.view.frame.size.height : kUpMargin;
 
 // 添加内容页面
 _contentScrollview = [[UIScrollView alloc] initWithFrame:CGRectMake(0, marginY + kTitleHeight + kButtonLineHeight, kFrameWidth, kFrameHeight - marginY - kTitleHeight - kButtonLineHeight)];
 _contentScrollview.pagingEnabled = YES;
 _contentScrollview.bounces = NO;
 _contentScrollview.contentSize = CGSizeMake(kFrameWidth * _pageCount, kFrameHeight - marginY - kTitleHeight);
 _contentScrollview.showsHorizontalScrollIndicator = NO;
 _contentScrollview.delegate = self;
 [self.view addSubview:_contentScrollview];
 
 // 添加分页面
 for (int i = 0; i < _pageCount; i++)
 {
  PageViewController *pageViewController = [[PageViewController alloc] init];
  UIButton *button = [_titleScrollView viewWithTag:1000 + i];
  pageViewController.title = button.currentTitle;
  pageViewController.view.frame = CGRectMake(kFrameWidth * i, 0, kFrameWidth, kFrameHeight - marginY - kTitleHeight);
  [_contentScrollview addSubview:pageViewController.view];
 }
 
 // 初始化后选中某个栏目
 [self titleButtonClicked:[_titleScrollView viewWithTag:1000 + 0]];
}
 
#pragma mark - 标题button点击事件
- (void)titleButtonClicked:(UIButton *)sender
{
 // 根据点击的button切换页面和偏移
 printf("%s clicked\n", sender.currentTitle.UTF8String);
 
 // 以下不用了，因为scroll切换会自动处理好尺寸和颜色了
// for (int i = 0; i < _pageCount; i++)
// {
//  UIButton *button = [_titleScrollView viewWithTag:1000 + i];
//  // 重置button尺寸颜色
//  button.transform = CGAffineTransformMakeScale(1, 1);
//  [button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
// }
 
 // 强调被选中的button
 // 放大聚焦
 sender.transform = CGAffineTransformMakeScale(kMaxTitleScale, kMaxTitleScale);
 // 变色
 [sender setTitleColor:[UIColor greenColor] forState:UIControlStateNormal];
 
 // 居中title
 [self settleTitleButton:sender];
 
 // 带动画切换到对应的内容,会触发scrollViewDidScroll
 NSInteger pageIndex = sender.tag - 1000;
 [_contentScrollview setContentOffset:CGPointMake(kFrameWidth * pageIndex, 0) animated:YES];
}
 
#pragma mark - scrollview滑动事件
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
 // 根据content内容偏移调整标题栏
 if (scrollView == _titleScrollView)
 {
  printf("title moved\n");
  
  
 }
 else if (scrollView == _contentScrollview)
 {
  printf("content moved\n");
  
  // 获得左右两个button的索引, 注意最后取整
  CGFloat offsetX = scrollView.contentOffset.x;
  NSInteger leftTitleIndex = offsetX / kFrameWidth;
  NSInteger rightTitleIndex = leftTitleIndex + 1;
  // 因为设置了到边不能滑动，所以不考虑边界
  UIButton *leftTitleButton = [_titleScrollView viewWithTag:1000 + leftTitleIndex];
  UIButton *rightTitleButton = [_titleScrollView viewWithTag:1000 + rightTitleIndex];
  
  // 设置大小和颜色渐变以及小横线的联动
  // 权重因子 0~1 小数, 左边和右边互补
  CGFloat rightTitleFactor = offsetX / kFrameWidth - leftTitleIndex;
  CGFloat leftTitleFactor = 1 - rightTitleFactor;
  
  // 尺寸
  CGFloat maxExtraScale = kMaxTitleScale - 1;
  leftTitleButton.transform = CGAffineTransformMakeScale(1 + leftTitleFactor * maxExtraScale, 1 + leftTitleFactor * maxExtraScale);
  rightTitleButton.transform = CGAffineTransformMakeScale(1 + rightTitleFactor * maxExtraScale, 1 + rightTitleFactor * maxExtraScale);
  // 颜色
  UIColor *leftTitleColor = [UIColor colorWithRed:0 green:leftTitleFactor blue:0 alpha:1];
  UIColor *rightTitleColor = [UIColor colorWithRed:0 green:rightTitleFactor blue:0 alpha:1];
  [leftTitleButton setTitleColor:leftTitleColor forState:UIControlStateNormal];
  [rightTitleButton setTitleColor:rightTitleColor forState:UIControlStateNormal];
  // 小横线位移
  _buttonLine.frame = CGRectMake(kButtonWidth * (leftTitleIndex + rightTitleFactor), _buttonLine.frame.origin.y, kButtonWidth, kButtonLineHeight);
 }
}
 
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
 // 内容区块滑动结束调整标题栏居中
 if (scrollView == _contentScrollview)
 {
  // 取得索引值
  NSInteger titleIndex = scrollView.contentOffset.x / kFrameWidth;
  // title居中
  [self settleTitleButton:[_titleScrollView viewWithTag:1000 + titleIndex]];
 }
}
 
#pragma mark - 标题按钮和横线居中偏移
- (void)settleTitleButton:(UIButton *)button
{
 // 标题
 // 这个偏移量是相对于scrollview的content frame原点的相对对标
 CGFloat deltaX = button.center.x - kFrameWidth / 2;
 // 设置偏移量，记住这段算法
 if (deltaX < 0)
 {
  // 最左边
  deltaX = 0;
 }
 CGFloat maxDeltaX = _titleScrollView.contentSize.width - kFrameWidth;
 if (deltaX > maxDeltaX)
 {
  // 最右边不能超范围
  deltaX = maxDeltaX;
 }
 [_titleScrollView setContentOffset:CGPointMake(deltaX, 0) animated:YES];
 
}