UIScrollView频道滑动（授人以鱼，不如授人以渔）

        内容型APP（比如新闻，视频），通常采用多个页面（频道）滑动；另外，自动滚动的焦点图用到比较多的。本文简单介绍使用UIScrollView实现上述功能的原理，并附部分代码。无论是频道的滑动，还是焦点图自动滑动，都是基于UIScrollView的特性，viewController 实现UIScrollView的代理，并做一些控制即可。
核心思想：
    ★使用UIScrollerview作为承载view。各个频道添加到UIScrollerview上。注意：UIScrollerview需要提前知道频道数量，进而确定UIScrollerview的frame.width
    ★当滑动屏幕一半儿的时候，调用UIScrollView 的- (void)scrollRectToVisible:(CGRect) animated:(BOOL)方法，实现整页滚动。
    ★当滑动屏幕不到一半儿的时候，由于启用了UIScrollView的pagingEnabled属性，所以，UIScrollView会自动弹回原位置。

关键代码：

- (void)viewDidLoad {    [super viewDidLoad];        self.scrollView = [[UIScrollView alloc] initWithFrame:self.bounds];   /*创建scrollerview*/    self.scrollView.pagingEnabled = YES; /*scroller 一页页滑动,而不是一直滑下去*/    self.scrollView.scrollsToTop = NO;       /*点击状态栏，是否滚到顶部。不*/    self.scrollView.bounces = YES;           /*到达边界回弹*/    self.scrollView.alwaysBounceHorizontal = YES;   /*如果水平方向，内容宽度小于bound，仍可以滑动回弹*/    self.scrollView.alwaysBounceVertical = NO;         /*如果垂直方向，内容高度小于bound，不让滑动回弹*/    self.scrollView.showsHorizontalScrollIndicator = NO;/*横向滚动条，不显示*/    self.scrollView.showsVerticalScrollIndicator = NO;    /*纵向滚动条，不显示*/        /*添加到viewController中的view之上*/    [self.view addSubview:self.scrollView];}========================================================================//内存警告的时候，卸载多余的page。保留current前后两个page- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];        for (NSInteger i = 0; i < [self.viewControllers count]; i++) {        if (i < self.currentPage - 1 || i > self.currentPage + 1) {            [self unloadViewControllerByPage:i];        }    }}========================================================================- (void)willScrollToPage:(NSInteger)page animated:(BOOL)animated {    //在滑动到page时候，处理逻辑。子类可重写该方法}- (void)didScrollToPage:(NSInteger)page animated:(BOOL)animated {    //在滑动到page时候，处理逻辑。子类可重写该方法    [self scrollToPage:index animated:YES];}========================================================================//跳转任意频道。- (void)scrollToPage:(NSInteger)page animated:(BOOL)animated {    NSInteger lastPage = self.currentPage;    [self setCurrentPage:page animated:animated];    if (self.currentPage != lastPage) {        [self removeViewControllerByPage:lastPage];    }            CGRect bounds = UIEdgeInsetsInsetRect(self.scrollView.bounds, self.scrollView.contentInset);        bounds.origin.x = CGRectGetWidth(bounds) * page;        bounds.origin.y = 0;    /* animated参数，一定要NO，不然滑动时候产生抖动 */    [self.scrollView scrollRectToVisible:bounds animated:NO];}========================================================================#pragma mark - UIScrollViewDelegate/*手指开始拖拽*/- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {    if (scrollView != self.scrollView) {        return;    }    //加载后一个，前一个page    [self addViewControllerByPage:self.currentPage - 1];    [self addViewControllerByPage:self.currentPage + 1];}- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView {    if (scrollView != self.scrollView) {        return;    }    //加载后一个，前一个page    [self addViewControllerByPage:self.currentPage - 1];    [self addViewControllerByPage:self.currentPage + 1];}- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {    if (scrollView != self.scrollView) {        return;    }        if (decelerate) {        return;    }        CGFloat width = CGRectGetWidth(scrollView.bounds);    CGFloat position = self.scrollView.contentOffset.x;    [self setCurrentPage:round(position / width) animated:YES];        if (!decelerate) {        for (NSInteger i = 0; i < self.numberOfPages; i++) {            if (i != self.currentPage) {                [self removeViewControllerByPage:i];            }        }    }}- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {    if (scrollView != self.scrollView) {        return;    }        CGFloat width = CGRectGetWidth(scrollView.bounds);    CGFloat position = self.scrollView.contentOffset.x;    [self setCurrentPage:round(position / width) animated:YES];        for (NSInteger i = 0; i < self.numberOfPages; i++) {        if (i != self.currentPage) {    //非移除currentPage            [self removeViewControllerByPage:i];        }    }}