iOS开发 剖析网易新闻标签栏视图切换(addChildViewController属性介绍)

转自：http://blog.csdn.net/hmt20130412/article/details/34523235

本来只是打算介绍一下addChildViewController这个方法的,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:(具体解释都写在了Demo里面的注释)

 //
 //  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",@"财经",@"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,大家可以去看看
      */
     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增加了addChildViewController方法，并且希望我们在使用addSubview时，同时调用[self addChildViewController:child]方法将sub view对应的viewController也加到当前ViewController的管理中。
      对于那些当前暂时不需要显示的subview，只通过addChildViewController把subViewController加进去；需要显示时再调用transitionFromViewController方法。将其添加进入底层的ViewController中。
      这样做的好处：

      1.无疑，对页面中的逻辑更加分明了。相应的View对应相应的ViewController。
      2.当某个子View没有显示时，将不会被Load，减少了内存的使用。
      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中新添加了下面几个方法：
      *  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,具体查看API)
      *  animations              转换过程中得动画
      *  completion              转换完成
      */

     [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;

         }
     }];
 }