iOS如何实现多控制器切换效果

//宏
#define kScreenWidth  [UIScreen mainScreen].bounds.size.width
#define kScreenHeight  [UIScreen mainScreen].bounds.size.height

#import "MYMainViewController.h"
#import "MYFirstViewController.h"
#import "MYSecondViewController.h"
#import "MYThirdViewController.h"

@interface MYMainViewController ()<UIScrollViewDelegate>
//控制器名
@property (nonatomic, strong) NSArray *VcNames;
//选择栏
@property(nonatomic, strong) UIView *clickBar;
//底部容器scrollView
@property (strong, nonatomic) UIScrollView *containerScrollerView;

@end

@implementation MYMainViewController

- (UIScrollView *)containerScrollerView
{
    if (!_containerScrollerView) {
        _containerScrollerView = [[UIScrollView alloc]init];
        _containerScrollerView.pagingEnabled = YES;
        _containerScrollerView.showsVerticalScrollIndicator = NO;
        _containerScrollerView.showsHorizontalScrollIndicator = NO;
        _containerScrollerView.contentSize = CGSizeMake(kScreenWidth *self.VcNames.count,kScreenHeight);
        _containerScrollerView.backgroundColor = [UIColor whiteColor];
        _containerScrollerView.delegate = self;
    }
    return _containerScrollerView;
}

//三个子控制器
- (NSArray *)VcNames
{
    if (!_VcNames) {
        _VcNames = @[@"控制器一",@"控制器二",@"控制器三"];
    }
    return _VcNames;
}

//点击选择栏
- (UIView *)clickBar
{
    if (!_clickBar) {
        _clickBar = [[UIView alloc]init];
        _clickBar.backgroundColor = [UIColor lightGrayColor];

        CGFloat width = kScreenWidth / 3;
        CGFloat height = 44;
        //初始化按钮
        for (NSInteger index = 0; index < 3; index++) {

            UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
            [button setTitle:self.VcNames[index] forState:UIControlStateNormal];
            [button setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
            button.frame = (CGRect){width *index,0,width,height};
            [button addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];

            //绑定tag值
            button.tag = index;
            [_clickBar addSubview:button];
        }
    }
    return _clickBar;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    self.edgesForExtendedLayout = 0;
    //初始化选择栏
    [self initClickBar];

    //初始化底部scrollView容器
    [self initScrollViewContainer];

    //初始化子控制器
    [self addChildControllers];

}

//按钮选择栏
- (void)initClickBar
{
    [self.view addSubview:self.clickBar];
    self.clickBar.frame = (CGRect){0,0,[UIScreen mainScreen].bounds.size.width,44};
}

//初始化滑动容器
- (void)initScrollViewContainer
{
    [self.view addSubview:self.containerScrollerView];
    self.containerScrollerView.frame = CGRectMake(0,44,kScreenWidth, kScreenHeight );
}

//添加子控制器
- (void)addChildControllers
{
    //为了方便直观 , 在此处设置背景色  (实际开发中,不能在这里设置 , 原因是这里只要调用到了控制器的view属性 , 该控制器将会执行viewDidLoad方法 , 相当于直接一开始就将三个控制器的所有UI和网络请求全加载完了 , 负荷会相当重)
    MYFirstViewController *firstVc = [[MYFirstViewController alloc]init];
    firstVc.view.backgroundColor = [UIColor redColor];
    [self addChildViewController:firstVc];

    MYSecondViewController *secondVc = [[MYSecondViewController alloc]init];
    secondVc.view.backgroundColor = [UIColor blueColor];
    [self addChildViewController:secondVc];

    MYThirdViewController *thirdVc = [[MYThirdViewController alloc]init];
    thirdVc.view.backgroundColor = [UIColor yellowColor];
    [self addChildViewController:thirdVc];

    //默认展示第一个子控制器
    [self scrollViewDidEndDecelerating:self.containerScrollerView];
}

//选择栏按钮点击事件
- (void)buttonClick:(UIButton *)button
{
    [self.containerScrollerView setContentOffset:CGPointMake(button.tag *kScreenWidth, 0) animated:YES];
}

//滑动减速时调用
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    //获取contentOffset
    CGPoint currentOffset = scrollView.contentOffset;

    NSInteger page = currentOffset.x / kScreenWidth;

    //取出对应控制器
    UIViewController *viewController = self.childViewControllers[ page ];

    //添加到scrollView容器
    //    if (![viewController isViewLoaded]) {

    [self.containerScrollerView addSubview:viewController.view];
    viewController.view.frame = CGRectMake(page *kScreenWidth, 0,kScreenWidth, kScreenHeight);
    //    }

}