iOS开发：仿网易新闻首页多频道视图切换

前言

1、相信筒子们在项目中会遇到像网易新闻这样的多频道视图切换需求，而这一功能需要考虑的东西也挺多，其中最主要的就是内存问题了。

2、这种多频道视图切换一般分为两部分：上滚动视图（顶部频道列表）和下滚动视图（频道内容展示）

3、上滚动视图基本上都会用UIScrollView来做，而下滚动视图则可采用UITableView或者UIScrollView来做，UITableView可以改善UIScrollView带来的内存问题，但在使用中不是很方便。

4、此Demo采用双滚动视图的方式来实现，主要有：视图切换（延迟加载，当用户滚动到对应频道才加载页面），滚动视图的位置调整，频道切换时标题的动态变化。 未实现：数据本地缓存，释放离当前频道比较远的页面资源来降低内存占用（此基于数据本地缓存）

思路

主要是采用addChildViewController来实现
版本一、在当前页直接切换，不采用滚动视图；
版本二、采用滚动视图

版本一：

1、定义数组和视图

@property (nonatomic,strong) UIViewController * currentVC;
@property (nonatomic,strong) UIButton * currentBtn;
@property (nonatomic,strong) UIScrollView * headScrollView;
@property (nonatomic,strong) NSArray * headTitleArray;
@property (nonatomic,strong) NSMutableArray * vcArray;

2、初始化数组

-(NSArray *)headTitleArray {if (!_headTitleArray) {_headTitleArray = [NSArray arrayWithObjects:@"头条",@"娱乐",@"热点",@"体育",@"广州",@"财经",@"科技", nil];}return _headTitleArray;
}-(NSMutableArray *)vcArray {if (!_vcArray ) {_vcArray = [[NSMutableArray alloc]init];//创建内容视图[self configVCArray];}return _vcArray;
}- (void)configVCArray {CGRect childVCRect = CGRectMake(0, 64 + HEADSCROLLVIEW_HEIGHT, SCREEN_WIDTH, SCREEN_HEIGHT - 64 - HEADSCROLLVIEW_HEIGHT);for (int i = 0; i < self.headTitleArray.count; i ++) {ContentViewController * VC = [[ContentViewController alloc]init];VC.typeName = self.headTitleArray[i];VC.view.frame = childVCRect;[_vcArray addObject:VC];}
}

3、配置上滚动视图

- (void)configHeadScrollView {self.headScrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 64, SCREEN_WIDTH, HEADSCROLLVIEW_HEIGHT)];self.headScrollView.backgroundColor = [UIColor purpleColor];self.headScrollView.contentSize = CGSizeMake(self.headTitleArray.count * 60, 40);self.headScrollView.bounces = NO;[self.view addSubview:self.headScrollView];[self addBtnsToHeadScrollView];
}- (void)addBtnsToHeadScrollView {for (int i = 0; i < self.headTitleArray.count; i ++) {UIButton * button = [UIButton buttonWithType:UIButtonTypeCustom];button.frame = CGRectMake(0 + 60 * i, 0, 60, 40);[button setTitle:self.headTitleArray[i] forState:UIControlStateNormal];[button setTag:1000 + i];[button.titleLabel setFont:[UIFont systemFontOfSize:12]];[self.headScrollView addSubview:button];[button addTarget:self action:@selector(headScrollViewButtonAction:) forControlEvents:UIControlEventTouchUpInside];//默认当前为第一个频道if (!i) {[button.titleLabel setFont:[UIFont systemFontOfSize:15]];[button setTitleColor:[UIColor yellowColor] forState:UIControlStateNormal];self.currentBtn = button;}}
}

4、配置默认显示的视图

- (void)configDefaultVC {//默认加载第一个标签页self.currentVC = self.vcArray[0];[self addChildViewController:self.currentVC];[self.view addSubview:self.currentVC.view];}

5、实现视图切换的方法

/***  移除当前VC，替换新的VC*/
- (void)switchNewVC:(UIViewController *)newViewController {//1、先加载新VC为ChildViewController[self addChildViewController:newViewController];//2、动画从当前VC切换到新VC/***  transitionFromViewController 方法更详细了解到：http://blog.csdn.net/yongyinmg/article/details/40619727交换两个子视图控制器的位置（由于添加的顺序不同，所以子试图控制器在父视图控制器中存在层次关系）fromViewController：当前显示的子试图控制器，将被替换为非显示状态toViewController：将要显示的子视图控制器duration：交换动画持续的时间，单位秒options：动画的方式animations：动画Blockcompletion：完成后执行的Block*/[self transitionFromViewController:self.currentVC toViewController:newViewController duration:0.2 options:UIViewAnimationOptionTransitionCrossDissolve animations:nil completion:^(BOOL finished) {if (finished) {//3、动画完毕后，移除旧VC，设置新VC为当前VC/**关于willMoveToParentViewController方法和didMoveToParentViewController方法的使用1.这两个方法用在子试图控制器交换的时候调用！即调用transitionFromViewController 方法时，调用。2.当调用willMoveToParentViewController方法或didMoveToParentViewController方法时，要注意他们的参数使用：当某个子视图控制器将从父视图控制器中删除时，parent参数为nil。即：[将被删除的子试图控制器 willMoveToParentViewController:nil];当某个子试图控制器将加入到父视图控制器时，parent参数为父视图控制器。即：[将被加入的子视图控制器 didMoveToParentViewController:父视图控制器];*/[newViewController didMoveToParentViewController:self];[self.currentVC willMoveToParentViewController:nil];[self.currentVC removeFromParentViewController];self.currentVC = newViewController;}}];
}

6、实现频道滚动视图点击的方法

- (void)headScrollViewButtonAction:(UIButton *)button {//点击频道按钮切换视图if (self.currentVC == self.vcArray[button.tag - 1000]) {//如果是当前频道，则不操作return;}else {//切换频道按钮[self.currentBtn.titleLabel setFont:[UIFont systemFontOfSize:12]];[self.currentBtn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];[button.titleLabel setFont:[UIFont systemFontOfSize:15]];[button setTitleColor:[UIColor yellowColor] forState:UIControlStateNormal];self.currentBtn = button;//切换VCNSInteger num = button.tag - 1000;[self switchNewVC:self.vcArray[num]];}
}

7、效果图

8、存在的问题和改进

问题：因为初始化VC数组把VC的view设置了Frame，因此VC会执行viewDidLoad方法，所以如果需要加载大量数据（或网络连接）的情况，要把这些方法放到viewWillApper或者DidApper来执行。
改进：可以在切换VC的时候才设置Frame

版本二：

1、声明数组和视图

@property (nonatomic,assign) int currentPage;
@property (nonatomic,strong) UIScrollView * headScrollView;
@property (nonatomic,strong) UIScrollView * contentScrollView;
@property (nonatomic,strong) NSArray * headTitleArray;

2、初始化

//频道列表
-(NSArray *)headTitleArray {if (!_headTitleArray) {_headTitleArray = [NSArray arrayWithObjects:@"头条",@"娱乐",@"热点",@"体育",@"广州",@"财经",@"科技", nil];}return _headTitleArray;
}pragma mark - 顶部频道配置
- (void)configHeadScrollView {self.headScrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 64, SCREEN_WIDTH, HEADSCROLLVIEW_HEIGHT)];self.headScrollView.backgroundColor = [UIColor purpleColor];self.headScrollView.contentSize = CGSizeMake(self.headTitleArray.count * 60, 40);self.headScrollView.bounces = NO;[self.view addSubview:self.headScrollView];[self addBtnsToHeadScrollView];
}//加频道按钮
- (void)addBtnsToHeadScrollView {for (int i = 0; i < self.headTitleArray.count; i ++) {UIButton * button = [UIButton buttonWithType:UIButtonTypeCustom];button.frame = CGRectMake(0 + 60 * i, 0, 60, 40);[button setTitle:self.headTitleArray[i] forState:UIControlStateNormal];[button setTag:1000 + i];[button.titleLabel setFont:[UIFont systemFontOfSize:15]];[self scaleButton:button withScale:0];[self.headScrollView addSubview:button];[button addTarget:self action:@selector(headScrollViewButtonAction:) forControlEvents:UIControlEventTouchUpInside];//默认当前为第一个频道if (!i) {[self scaleButton:button withScale:1];}}
}pragma mark - 配置内容ScrollView
- (void)configContentScrollView {CGRect contentScrollViewRect = CGRectMake(0, 64 + HEADSCROLLVIEW_HEIGHT, SCREEN_WIDTH, SCREEN_HEIGHT - 64 - HEADSCROLLVIEW_HEIGHT);self.contentScrollView = [[UIScrollView alloc]initWithFrame:contentScrollViewRect];self.contentScrollView.contentSize = CGSizeMake(SCREEN_WIDTH * self.headTitleArray.count, contentScrollViewRect.size.height);self.contentScrollView.bounces = NO;self.contentScrollView.pagingEnabled = YES;self.contentScrollView.delegate = self;[self.view addSubview:self.contentScrollView];[self addContentVC];
}

3、加入视图控制器

/***  加入视图控制器1、先加入ChildViewController   无2、设置frame                   VC会调用viewDidLoad方法3、加入superView               VC会调用viewWillApper、viewDidApper方法*/
- (void)addContentVC {for (int i = 0; i < self.headTitleArray.count; i ++) {ContentViewController * VC = [[ContentViewController alloc]init];VC.typeName = self.headTitleArray[i];[self addChildViewController:VC];//默认加载第一页if (!i) {[self loadScrollViewWithPage:i];}}
}

4、实现视图切换的方法

- (CGRect)getRect:(int)currentPage {CGRect rect = CGRectMake(SCREEN_WIDTH * currentPage, 0, SCREEN_WIDTH, SCREEN_HEIGHT - 64 - HEADSCROLLVIEW_HEIGHT);return rect;
}- (void)loadScrollViewWithPage:(int)page {if (page < 0 || page >= self.headTitleArray.count) {return;}//判断页面是否已经显示，如果未显示则让其显示ContentViewController * VC = [self.childViewControllers objectAtIndex:page];if (VC.view.superview == nil) {VC.view.frame = [self getRect:page];[self.contentScrollView addSubview:VC.view];}else {return;}}

5、实现频道切换时上滚动视图的图标实时变化

//改变按钮大小
- (void)scaleButton:(UIButton *)button withScale:(CGFloat)scale {[button setTitleColor:[UIColor colorWithRed:1.0 green:1.0 blue:1.0 - scale alpha:1.0] forState:UIControlStateNormal];CGFloat minScale = 0.8;CGFloat trueScale = minScale + (1 - minScale) * scale;button.transform = CGAffineTransformMakeScale(trueScale, trueScale);
}//改变频道按钮的坐标
- (void)scrollHeadScrollView {CGFloat x = self.currentPage * 60 + 60 * 0.5 - SCREEN_WIDTH * 0.5;if (x >= 0) {if (x >= self.headScrollView.contentSize.width - SCREEN_WIDTH) {x = self.headScrollView.contentSize.width - SCREEN_WIDTH;[self.headScrollView setContentOffset:CGPointMake(x, 0) animated:YES];   //向右滚动到尽头}else[self.headScrollView setContentOffset:CGPointMake(x, 0) animated:YES];}else[self.headScrollView setContentOffset:CGPointMake(0, 0) animated:YES];  //向左滚动到尽头
}//点击频道按钮切换
- (void)headScrollViewButtonAction:(UIButton *)button {NSInteger currentPage = button.tag - 1000;[self.contentScrollView setContentOffset:CGPointMake(SCREEN_WIDTH * currentPage, 0) animated:YES];}

6、在ScrollView代理方法里面实现切换视图的判断

pragma mark - scrollViewDelegate
//用户滑动屏幕切换频道的情景：ScrollView滚动停止的时候调用该方法
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {if (scrollView == self.contentScrollView) {CGFloat pageWidth = SCREEN_WIDTH;self.currentPage = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;//加载页面[self loadScrollViewWithPage:self.currentPage];//滚动标题栏[self scrollHeadScrollView];//修正切换太快导致频道按钮出现缩放不正确的问题[self.headScrollView.subviews enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {if ([obj isKindOfClass:[UIButton class]] && idx != self.currentPage) {[self scaleButton:obj withScale:0];}}];}}//用户点击导航频道切换内容的情景：
// 调用以下函数，来自动滚动到想要的位置，此过程中设置有动画效果，停止时，触发该函数
// UIScrollView的setContentOffset:animated:
// UIScrollView的scrollRectToVisible:animated:
// UITableView的scrollToRowAtIndexPath:atScrollPosition:animated:
// UITableView的selectRowAtIndexPath:animated:scrollPosition:
- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {[self scrollViewDidEndDecelerating:self.contentScrollView];
}//用户滑动屏幕的情况：实时改变频道按钮的大小
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {CGFloat value = scrollView.contentOffset.x / SCREEN_WIDTH;//计算出需要改变大小的按钮的位置int leftBtnIndex = (int)value;int rightBtnIndex = leftBtnIndex + 1;//计算出需要改变大小的倍数CGFloat rightScale = value - leftBtnIndex;CGFloat leftScale = 1 - rightScale;//改变大小UIButton * leftBtn = [self.headScrollView.subviews objectAtIndex:leftBtnIndex];[self scaleButton:leftBtn withScale:leftScale];if (rightBtnIndex < self.headTitleArray.count) {UIButton * rightBtn = [self.headScrollView.subviews objectAtIndex:rightBtnIndex];[self scaleButton:rightBtn withScale:rightScale];}}

7、效果图

8、demo下载

下载地址（点击我）https://github.com/DaMingShen/Imitate163PageControlDemo