iOS仿网易新闻滚动导航条效果

// 头条ViewController, 其它控制器和这个控制器都一样，只是背景颜色不同而已
#import <UIKit/UIKit.h>
@interface TopLineViewController : UIViewController

@end
//----------------------------------------------------------------
#import "TopLineViewController.h"
@interface TopLineViewController ()

@end

@implementation TopLineViewController
- (void)viewDidLoad {
  [super viewDidLoad];

  self.view.backgroundColor = [UIColor blackColor];
}
@end

#import <UIKit/UIKit.h>
@interface ViewController : UIViewController

@end
//----------------------------------------------------------------
#import "ViewController.h"
#import "TopLineViewController.h"
#import "TechnologyViewController.h"
#import "CarViewController.h"
#import "SportsViewController.h"
#import "VideoViewController.h"
#import "ImageViewController.h"
#import "HotViewController.h"

#define ScreenWidth [UIScreen mainScreen].bounds.size.width
#define ScreenHeight [UIScreen mainScreen].bounds.size.height

@interface ViewController () <UIScrollViewDelegate>

@property (weak, nonatomic) IBOutlet UIScrollView *titleScrollView;

@property (weak, nonatomic) IBOutlet UIScrollView *contentScrollView;

@property (strong, nonatomic) NSMutableArray *buttons;
@property (strong, nonatomic) UIButton *selectedButton;

@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  self.navigationItem.title = @"网易新闻";
  // 1. 初始化标题滚动视图上的按钮
  [self initButtonsForButtonScrollView];


}


- (void) initButtonsForButtonScrollView {
  // 初始化子控制器
  [self initChildViewControllers];
  CGFloat buttonWidth = 100;
  CGFloat buttonHeight = 40;
  NSInteger childViewControllerCount = self.childViewControllers.count;
  for (NSInteger i = 0; i < childViewControllerCount; i++) {
    UIViewController *childViewController = self.childViewControllers[i];
    UIButton *titleButton = [UIButton buttonWithType:UIButtonTypeCustom];
    titleButton.tag = i;
    CGFloat x = i * buttonWidth;
    titleButton.frame = CGRectMake(x, 0, buttonWidth, buttonHeight);
    [titleButton setTitle:childViewController.title forState:UIControlStateNormal];
    [titleButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [titleButton addTarget:self action:@selector(titleButtonOnClick:) forControlEvents:UIControlEventTouchUpInside];
    [self.titleScrollView addSubview:titleButton];

    [self.buttons addObject:titleButton];
  }

  self.titleScrollView.contentSize = CGSizeMake(buttonWidth * childViewControllerCount, 0);
  self.titleScrollView.showsHorizontalScrollIndicator = NO;
  self.titleScrollView.bounces = NO;

  self.contentScrollView.contentSize = CGSizeMake(ScreenWidth * childViewControllerCount, 0);
  self.contentScrollView.showsHorizontalScrollIndicator = NO;
  self.contentScrollView.pagingEnabled = YES;
  self.contentScrollView.delegate = self;

  // 禁止额外滚动区域
  self.automaticallyAdjustsScrollViewInsets = NO;

  // 初始化时默认选中第一个
  [self titleButtonOnClick:self.buttons[0]];
}


- (void)titleButtonOnClick:(UIButton *)button {
  // 1. 选中按钮
  [self selectingButton:button];

  // 2. 显示子视图
  [self addViewToContentScrollView:button];
}

- (void)selectingButton:(UIButton *)button {
  [_selectedButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  _selectedButton.transform = CGAffineTransformMakeScale(1.0, 1.0);
  [button setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
  button.transform = CGAffineTransformMakeScale(1.3, 1.3); // 选中字体变大，按钮变大，字体也跟着变大
  _selectedButton = button;

  // 选中按钮时要让选中的按钮居中
  CGFloat offsetX = button.frame.origin.x - ScreenWidth * 0.5;
  CGFloat maxOffsetX = self.titleScrollView.contentSize.width - ScreenWidth;

  if (offsetX < 0) {
    offsetX = 0;
  } else if (offsetX > maxOffsetX) {
    offsetX = maxOffsetX;
  }

  [self.titleScrollView setContentOffset:CGPointMake(offsetX, 0) animated:YES];
}

- (void)addViewToContentScrollView:(UIButton *)button {
  NSInteger i = button.tag;
  UIViewController *childViewController = self.childViewControllers[i];
  CGFloat x = i * ScreenWidth;

  // 防止添加多次
  if (childViewController.view.subviews != nil) {
    childViewController.view.frame = CGRectMake(x, 0, ScreenWidth, ScreenHeight);
    [self.contentScrollView addSubview:childViewController.view];
  }
  self.contentScrollView.contentOffset = CGPointMake(x, 0);
}

#pragma mark - UIScrollViewDelegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {


}

// 滚动结束时，将对应的视图控制器的视图添加到内容滚动视图中
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
  NSInteger i = self.contentScrollView.contentOffset.x / ScreenWidth;
  [self addViewToContentScrollView:_buttons[i]];

  // 内容滚动视图结束后选中对应的标题按钮
  [self selectingButton:_buttons[i]];
}

- (void)initChildViewControllers {
  // 0.头条
  TopLineViewController * topViewController = [[TopLineViewController alloc] init];
  topViewController.title = @"头条";
  [self addChildViewController:topViewController];

  // 1.科技
  TechnologyViewController * technologyViewController = [[TechnologyViewController alloc] init];
  technologyViewController.title = @"科技";
  [self addChildViewController:technologyViewController];

  // 2.汽车
  CarViewController * carViewController = [[CarViewController alloc] init];
  carViewController.title = @"汽车";
  [self addChildViewController:carViewController];

  // 3.体育
  SportsViewController * sportsViewController = [[SportsViewController alloc] init];
  sportsViewController.title = @"体育";
  [self addChildViewController:sportsViewController];

  // 4.视频
  VideoViewController * videoViewController = [[VideoViewController alloc] init];
  videoViewController.title = @"视频";
  [self addChildViewController:videoViewController];

  // 5.图片
  ImageViewController * imageViewController = [[ImageViewController alloc] init];
  imageViewController.title = @"图片";
  [self addChildViewController:imageViewController];

  // 6.热点
  HotViewController * hotViewController = [[HotViewController alloc] init];
  hotViewController.title = @"热点";
  [self addChildViewController:hotViewController];
}

- (NSMutableArray *)buttons {
  if (_buttons == nil) {
    _buttons = [NSMutableArray array];
  }

  return _buttons;
}
@end