//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;
//選擇欄
@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;
}

//三個子控制器
- (NSArray *)VcNames
{
? ? if (!_VcNames) {
? ? ? ? _VcNames = @[@"控制器一",@"控制器二",@"控制器三"];
? ? }
? ? return _VcNames;
}

//點擊選擇欄
- (UIView *)clickBar
{
? ? if (!_clickBar) {
? ? ? ? _clickBar = [[UIView alloc]init];
? ? ? ? _clickBar.backgroundColor = [UIColor lightGrayColor];

? ? ? ? CGFloat width = kScreenWidth / 3;
? ? ? ? CGFloat height = 44;
? ? ? ? //初始化按鈕
? ? ? ? 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];

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

- (void)viewDidLoad {
? ? [super viewDidLoad];

? ? self.edgesForExtendedLayout = 0;
? ? //初始化選擇欄
? ? [self initClickBar];

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

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

}

//按鈕選擇欄
- (void)initClickBar
{
? ? [self.view addSubview:self.clickBar];
? ? self.clickBar.frame = (CGRect){0,0,[UIScreen mainScreen].bounds.size.width,44};
}

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

//添加子控制器
- (void)addChildControllers
{
? ? //為了方便直觀 , 在此處設置背景色 ?(實際開發中,不能在這里設置 , 原因是這里只要調用到了控制器的view屬性 , 該控制器將會執行viewDidLoad方法 , 相當于直接一開始就將三個控制器的所有UI和網絡請求全加載完了 , 負荷會相當重)
? ? 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];

? ? //默認展示第一個子控制器
? ? [self scrollViewDidEndDecelerating:self.containerScrollerView];
}

//選擇欄按鈕點擊事件
- (void)buttonClick:(UIButton *)button
{
? ? [self.containerScrollerView setContentOffset:CGPointMake(button.tag *kScreenWidth, 0) animated:YES];
}

//滑動減速時調用
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
? ? //獲取contentOffset
? ? CGPoint currentOffset = scrollView.contentOffset;

? ? NSInteger page = currentOffset.x / kScreenWidth;

? ? //取出對應控制器
? ? 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);
? ? // ? ?}

}