ChildViewController的应用

viewControlle中可以添加多个subView，在需要的时候显示出来；另一种方法是通过向parentViewController中可以添加多个childCiewController;来控制页面中的subView，降低代码耦合度；通过切换子视图控制器，可以显示不同的view；，替代之前的addSubView的管理。

本节通过类似百度新闻模块切换的界面来演示ChileViewController的应用：

文档结构：

代码演示：

#import "MainViewController.h"
#import "FirstViewController.h"
#import "SecondViewController.h"
#import "ThirdViewController.h"
@interface MainViewController ()
@property (nonatomic, strong) FirstViewController *firstVC;
@property (nonatomic, strong) SecondViewController *secondVC;
@property (nonatomic, strong) ThirdViewController *thirdVC;
@property (nonatomic, strong) UIViewController *currentVC;

@property (nonatomic, strong) UIScrollView *headScrollView;
@property (nonatomic, strong) NSMutableArray *itemArray;
@property (nonatomic, strong) UIView *contentView;
@end

@implementation MainViewController
- (void)loadView{
    [super loadView];
    [self initialization];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    [self loadBaseUI];
}

- (void)initialization{
    _itemArray = [NSMutableArray arrayWithObjects:@"头条",@"今日",@"焦点", nil];
}

- (void)loadBaseUI{
    self.title = @"首页";
    _headScrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, 44)];
    _headScrollView.backgroundColor = [UIColor colorWithWhite:0.902 alpha:1.000];
    for (int i = 0; i<_itemArray.count; i++) {
        UIButton *itemButton = [[UIButton alloc]initWithFrame:CGRectMake(i*([UIScreen mainScreen].bounds.size.width/_itemArray.count), 0, [UIScreen mainScreen].bounds.size.width/_itemArray.count, 44)];
        itemButton.tag = 100+i;
        itemButton.backgroundColor = [UIColor clearColor];
        NSDictionary *dic = @{NSForegroundColorAttributeName:[UIColor purpleColor],NSFontAttributeName:[UIFont systemFontOfSize:14.0f]};
        [itemButton setAttributedTitle:[[NSAttributedString alloc]initWithString:_itemArray[i] attributes:dic] forState:UIControlStateNormal];
        [itemButton addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];
        [_headScrollView addSubview:itemButton];
    }
    [_headScrollView setContentSize:CGSizeMake([UIScreen mainScreen].bounds.size.width, 44)];
    _headScrollView.showsHorizontalScrollIndicator = NO;
    _headScrollView.showsVerticalScrollIndicator = NO;
    [self.view addSubview:_headScrollView];

    _contentView = [[UIView alloc]initWithFrame:CGRectMake(0, 44, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height - 44 - 64)];
    _contentView.backgroundColor = [UIColor clearColor];
    [self.view addSubview:_contentView];

    [self addSubControllers];
}

#pragma mark - privatemethods
- (void)addSubControllers{
    _firstVC = [[FirstViewController alloc]initWithNibName:@"FirstViewController" bundle:nil];
    [self addChildViewController:_firstVC];

    _secondVC = [[SecondViewController alloc]initWithNibName:@"SecondViewController" bundle:nil];
    [self addChildViewController:_secondVC];

    _thirdVC = [[ThirdViewController alloc]initWithNibName:@"ThirdViewController" bundle:nil];
    [self addChildViewController:_thirdVC];

    //调整子视图控制器的Frame已适应容器View
    [self fitFrameForChildViewController:_firstVC];
    //设置默认显示在容器View的内容
    [self.contentView addSubview:_firstVC.view];

    NSLog(@"%@",NSStringFromCGRect(self.contentView.frame));
    NSLog(@"%@",NSStringFromCGRect(_firstVC.view.frame));

    _currentVC = _firstVC;
}

- (void)buttonClick:(UIButton *)sender{
    if ((sender.tag == 100 && _currentVC == _firstVC) || (sender.tag == 101 && _currentVC == _secondVC) || (sender.tag == 102 && _currentVC == _thirdVC)) {
        return;
    }
    switch (sender.tag) {
        case 100:{
            [self fitFrameForChildViewController:_firstVC];
            [self transitionFromOldViewController:_currentVC toNewViewController:_firstVC];
        }
            break;
        case 101:{
            [self fitFrameForChildViewController:_secondVC];
            [self transitionFromOldViewController:_currentVC toNewViewController:_secondVC];
        }
            break;
        case 102:{
            [self fitFrameForChildViewController:_thirdVC];
            [self transitionFromOldViewController:_currentVC toNewViewController:_thirdVC];
        }
            break;
    }
}

- (void)fitFrameForChildViewController:(UIViewController *)chileViewController{
    CGRect frame = self.contentView.frame;
    frame.origin.y = 0;
    chileViewController.view.frame = frame;
}

//转换子视图控制器
- (void)transitionFromOldViewController:(UIViewController *)oldViewControllertoNewViewController:(UIViewController *)newViewController{
    [self transitionFromViewController:oldViewController toViewController:newViewController duration:0.3 options:UIViewAnimationOptionTransitionCrossDissolve animations:nil completion:^(BOOL finished) {
        if (finished) {
            [newViewController didMoveToParentViewController:self];
            _currentVC = newViewController;
        }else{
            _currentVC = oldViewController;
        }
    }];
}

//移除所有子视图控制器
- (void)removeAllChildViewControllers{
    for (UIViewController *vc in self.childViewControllers) {
        [vc willMoveToParentViewController:nil];
        [vc removeFromParentViewController];
    }
}

/**
 *  方法说明：
 *  1、addChildViewController:向父VC中添加子VC，添加之后自动调用willMoveToParentViewController:父VC
 *  2、removeFromParentViewController:将子VC从父VC中移除，移除之后自动调用
    didMoveToParentViewController:nil
 *  3、willMoveToParentViewController:  当向父VC添加子VC之后，该方法会自动调用。若要从父VC移除子VC，需要在移除之前调用该方法，传入参数nil。
 *  4、didMoveToParentViewController:  当向父VC添加子VC之后，该方法不会被自动调用，需要显示调用告诉编译器已经完成添加（事实上不调用该方法也不会有问题，不太明白）; 从父VC移除子VC之后，该方法会自动调用，传入的参数为nil,所以不需要显示调用。
 */

/**
 *  注意点：
    要想切换子视图控制器a/b,a/b必须均已添加到父视图控制器中，不然会报错
 */
@end

最终效果：(实现了3个视图之间的切换)