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

　　原文：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;

        }
    }];
}