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Block
completion：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VC
NSInteger 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