图片轮播——不间断切换

可以使用UIScrollView、UIPageControl、NSTimer来创建，scrollview是图片的展示区域，UIPageControl是一行小圆点，用来表示当前展示的是多页面中的第几页，NSTimer用来循环执行某事件。
这里边比较重要的方法是scrollViewDidScroll，就是当scrollview滚动时计算当前pageControl的页码。

效果如下：

关于UIScrollView
contentSize是scrollView可以滚动的区域，类型为CGSize，表示尺寸。
如frame=(0,0,320,480)，contentSize=(640宽,480高)，表示scrollview只能左右移动，上下是不能滚动的。
contentOffSet是当前显示区域的顶点相对于frame顶点的偏移量，类型为CGPoint，表示坐标。
如上边当把scrollView滑到最右边，contentoffSet就是(320,0)，也就是x偏移了320。

这里的数据源，即图片名称是写死的，格式为img_01，img_02这样的。下边是代码：

  1 #define imgCount    5
  2 
  3 @interface ViewController ()<UIScrollViewDelegate>
  4 
  5 /** 图片展示区 */
  6 @property(nonatomic,strong) UIScrollView *imgShowView;
  7 /** 图片切换按钮,UIPageControl提供一行点来指示当前显示的是多页面中的哪一页 */
  8 @property(nonatomic,strong) UIPageControl *pageControl;
  9 /** 定时器 */
 10 @property(nonatomic,strong) NSTimer *imgTimer;
 11 
 12 @end
 13 
 14 @implementation ViewController
 15 
 16 - (void)viewDidLoad {
 17     [super viewDidLoad];
 18     
 19     //下面这两行代码顺序不能调换，否则代理方法不执行。因为setUpBackGroundView是实例化了一个imgShowView，
 20     //若先执行self.imgShowView.delegate = self那么imgShowView是nil，空对象是不能执行方法的
 21     [self setUpBackGroundView];
 22     
 23     self.imgShowView.delegate = self;
 24     
 25     [self setUpTimer];
 26     
 27     [self setUpPageControl];
 28 }
 29 
 30 -(void)setUpBackGroundView{
 31     //图片展示区域
 32     CGFloat scrollViewW = self.view.frame.size.width - 100;
 33     CGFloat scrollViewH = 300;
 34     CGFloat scrollViewX = (self.view.frame.size.width - scrollViewW)/2;
 35     CGFloat scrollViewY = 90;
 36     UIScrollView *scrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(scrollViewX, scrollViewY, scrollViewW, scrollViewH)];
 37     self.imgShowView = scrollView;
 38     [self.view addSubview:self.imgShowView];
 39     
 40     //图片区
 41     CGFloat imgViewW = scrollViewW;
 42     CGFloat imgViewH = scrollViewH;
 43     CGFloat imgViewY = 0;
 44     for (int i=0; i<imgCount; i++) {
 45         CGFloat imgViewX = i*imgViewW;
 46         UIImageView *imgView = [[UIImageView alloc]initWithFrame:CGRectMake(imgViewX, imgViewY, imgViewW, imgViewH)];
 47         
 48         NSString *imgName = [NSString stringWithFormat:@"img_0%d",i+1];
 49         imgView.image = [UIImage imageNamed:imgName];
 50         [self.imgShowView addSubview:imgView];
 51     }
 52     
 53     //设置混动区域scrollView宽度
 54     CGFloat contentW = imgCount * imgViewW;
 55     self.imgShowView.contentSize = CGSizeMake(contentW, 0);
 56     //水平滚动条
 57     self.imgShowView.showsHorizontalScrollIndicator = NO;
 58     //根据scrollView的宽度来分页
 59     self.imgShowView.pagingEnabled = YES;
 60 //    self.imgShowView.clipsToBounds = NO;
 61 }
 62 
 63 -(void)setUpTimer{
 64     NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(showNextImage) userInfo:nil repeats:YES];
 65     self.imgTimer = timer;
 66     //将定时器添加到当前线程,NSRunLoopCommonModes表示始终坚挺滚动事件
 67     [[NSRunLoop currentRunLoop] addTimer:self.imgTimer forMode:NSRunLoopCommonModes];
 68 }
 69 
 70 //设置分页显示
 71 -(void)setUpPageControl{
 72     CGFloat pageControlW = 100;
 73     CGFloat pageControlH = 80;
 74     CGFloat pageControlX = (self.view.frame.size.width - pageControlW)/2;
 75     UIPageControl *pageControl = [[UIPageControl alloc]initWithFrame:CGRectMake(pageControlX, 320, pageControlW, pageControlH)];
 76     pageControl.numberOfPages = imgCount;
 77     pageControl.currentPage = 0;
 78     //当前页小圆点颜色
 79     pageControl.currentPageIndicatorTintColor = [UIColor redColor];
 80     //其余点的颜色
 81     pageControl.pageIndicatorTintColor = [UIColor blueColor];
 82     self.pageControl = pageControl;
 83     [self.view addSubview:self.pageControl];
 84 }
 85 
 86 //销毁定时器
 87 -(void)delImgTimer{
 88     [self.imgTimer invalidate];
 89     self.imgTimer = nil;
 90 }
 91                       
 92 -(void)showNextImage{
 93    //默认当前页码为0，若为最后一页，那么当前页变为第1页；若不是，则页码加1
 94     NSInteger pageIndexNum = 0;
 95     if (self.pageControl.currentPage == imgCount-1) {
 96         pageIndexNum = 0;
 97     } else {
 98         pageIndexNum = self.pageControl.currentPage + 1;
 99     }
100     
101     //计算scrollView滚动位置
102     CGFloat offsetX = pageIndexNum * self.imgShowView.frame.size.width;
103     CGPoint offset = CGPointMake(offsetX, 0);
104     [self.imgShowView setContentOffset:offset animated:YES];
105 }
106 
107 #pragma mark 代理方法
108 //开始拖拽scrollView调用
109 -(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
110     [self delImgTimer];
111 }
112 
113 //停止拖拽scrollView调用
114 -(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
115     [self setUpTimer];
116 }
117 
118 -(void)scrollViewDidScroll:(UIScrollView *)scrollView{
119     //根据scrollView的滚动位置决定pageControl显示第几页
120     CGFloat theScrollViewW = scrollView.frame.size.width;
121     CGFloat a = scrollView.contentOffset.x;
122 //    NSLog(@"偏移的x方向距离为%f",a);
123     NSInteger pageIndex = (scrollView.contentOffset.x + theScrollViewW * 0.5)/theScrollViewW;
124     self.pageControl.currentPage = pageIndex;
125 }