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

            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;
				
		}
	}];
}
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