本来仅仅是打算介绍一下addChildViewController这种方法的,正好今天朋友去换工作面试问到网易新闻标签栏效果的实现,就结合它,用个小Demo实例介绍一下:(详细解释都写在了Demo里面的凝视)

//
//  HMTMainViewController.m
//  UIScrollView
//
//  Created by HMT on 14-6-25.
//  Copyright (c) 2014年 humingtao. All rights reserved.
//#import "HMTMainViewController.h"
#import "HMTFirstViewController.h"
#import "HMTSecondViewController.h"
#import "HMTThirdViewController.h"@interface HMTMainViewController () <UIScrollViewDelegate>@property (nonatomic ,strong) HMTThirdViewController  *thirdVC;
@property (nonatomic ,strong) HMTFirstViewController  *firstVC;
@property (nonatomic ,strong) HMTSecondViewController *secondVC;@property (nonatomic ,strong) UIViewController *currentVC;@property (nonatomic ,strong) UIScrollView *headScrollView;  //  顶部滚动视图@property (nonatomic ,strong) NSArray *headArray;@end@implementation HMTMainViewController- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];if (self) {// Custom initialization}return self;
}- (void)viewDidLoad
{[super viewDidLoad];// Do any additional setup after loading the view.self.navigationItem.title = @"网易新闻Demo";self.headArray = @[@"头条",@"娱乐",@"体育",@"財经",@"科技",@"NBA",@"手机"];/***   automaticallyAdjustsScrollViewInsets   又被这个属性坑了*   我"UI高级"里面一篇文章着重讲了它,大家能够去看看*/self.automaticallyAdjustsScrollViewInsets = NO;self.headScrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 64, 320, 40)];self.headScrollView.backgroundColor = [UIColor purpleColor];self.headScrollView.contentSize = CGSizeMake(560, 0);self.headScrollView.bounces = NO;self.headScrollView.pagingEnabled = YES;[self.view addSubview:self.headScrollView];for (int i = 0; i < [self.headArray count]; i++) {UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];button.frame = CGRectMake(0 + i*80, 0, 80, 40);[button setTitle:[self.headArray objectAtIndex:i] forState:UIControlStateNormal];button.tag = i + 100;[button addTarget:self action:@selector(didClickHeadButtonAction:) forControlEvents:UIControlEventTouchUpInside];[self.headScrollView addSubview:button];}/*苹果新的API添加了addChildViewController方法，而且希望我们在使用addSubview时，同一时候调用[self addChildViewController:child]方法将sub view相应的viewController也加到当前ViewController的管理中。对于那些当前临时不须要显示的subview，仅仅通过addChildViewController把subViewController加进去；须要显示时再调用transitionFromViewController方法。

将其加入进入底层的ViewController中。 这样做的优点： 1.无疑，对页面中的逻辑更加分明了。相应的View相应相应的ViewController。

2.当某个子View没有显示时，将不会被Load，降低了内存的使用。 3.当内存紧张时，没有Load的View将被首先释放，优化了程序的内存释放机制。 */ /** * 在iOS5中。ViewController中新加入了以下几个方法： * addChildViewController: * removeFromParentViewController * transitionFromViewController:toViewController:duration:options:animations:completion: * willMoveToParentViewController: * didMoveToParentViewController: */ self.firstVC = [[HMTFirstViewController alloc] init]; [self.firstVC.view setFrame:CGRectMake(0, 104, 320, 464)]; [self addChildViewController:_firstVC]; self.secondVC = [[HMTSecondViewController alloc] init]; [self.secondVC.view setFrame:CGRectMake(0, 104, 320, 464)]; self.thirdVC = [[HMTThirdViewController alloc] init]; [self.thirdVC.view setFrame:CGRectMake(0, 104, 320, 464)]; // 默认,第一个视图(你会发现,全程就这一个用了addSubview) [self.view addSubview:self.firstVC.view]; self.currentVC = self.firstVC; } - (void)didClickHeadButtonAction:(UIButton *)button { // 点击处于当前页面的按钮,直接跳出 if ((self.currentVC == self.firstVC && button.tag == 100)||(self.currentVC == self.secondVC && button.tag == 101.)) { return; }else{ // 展示2个,其余一样,自行补全噢 switch (button.tag) { case 100: [self replaceController:self.currentVC newController:self.firstVC]; break; case 101: [self replaceController:self.currentVC newController:self.secondVC]; break; case 102: //....... break; case 103: //....... break; case 104: //....... break; case 105: //....... break; case 106: //....... break; //....... default: break; } } } // 切换各个标签内容 - (void)replaceController:(UIViewController *)oldController newController:(UIViewController *)newController { /** * 着重介绍一下它 * transitionFromViewController:toViewController:duration:options:animations:completion: * fromViewController 当前显示在父视图控制器中的子视图控制器 * toViewController 将要显示的姿势图控制器 * duration 动画时间(这个属性,old friend 了 O(∩_∩)O) * options 动画效果(渐变,从下往上等等,详细查看API) * animations 转换过程中得动画 * completion 转换完毕 */ [self addChildViewController:newController]; [self transitionFromViewController:oldController toViewController:newController duration:2.0 options:UIViewAnimationOptionTransitionCrossDissolve animations:nil completion:^(BOOL finished) { if (finished) { [newController didMoveToParentViewController:self]; [oldController willMoveToParentViewController:nil]; [oldController removeFromParentViewController]; self.currentVC = newController; }else{ self.currentVC = oldController; } }]; }