UIScrollView,UIPageControl,UIImageView 实现图片轮播的效果

上一篇博客介绍了如何将XCode创立的项目提交到Git版本控制,这次就直接做一个图片轮播的展示demo，刚好可以把UIScrollView、UIPageControl、UIImageView这三个控件讲解分析一下。先上效果，这样比较直观。

从图中可以看到这个界面是由UIImageView 和 UITableView 组合而成。在这里UITableView的内容不作为本次讲解的重点，如果对UITableView的使用有疑问的，可以留言给我。下面就进入正题，在头文件创建几个变量。

 @interface ScrollImageViewController : UIViewController<UIScrollViewDelegate>
 {
     BOOL isFromStart;
 }

 @property(nonatomic, strong)UIScrollView  *scrollView;      //声明一个UIScrollView
 @property(nonatomic, strong)UIPageControl *pageControl;     //声明一个UIPageControl
 @property(nonatomic, strong)NSArray  *arrayImages;          //存放图片的数组
 @property(nonatomic, strong)NSMutableArray *viewController; //存放UIViewController的可变数组
 @end

下面在.m文件中创建这些声明变量

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     // Do any additional setup after loading the view.

     self.arrayImages = [NSArray arrayWithObjects:[UIImage imageNamed:@"3201.jpg"],[UIImage imageNamed:@"3202.jpg"],[UIImage imageNamed:@"3203.jpg"],[UIImage imageNamed:@"3204.jpg"], nil];

     _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(, , self.view.frame.size.width,ImageHeight)];
     [_scrollView setPagingEnabled:YES];
     _scrollView.showsHorizontalScrollIndicator = NO;
     _scrollView.showsVerticalScrollIndicator = NO;
     [_scrollView setDelegate:self];
     [_scrollView setBackgroundColor:[UIColor lightGrayColor]];

     //ContentSize 这个属性对于UIScrollView挺关键的，取决于是否滚动。
     [_scrollView setContentSize:CGSizeMake(CGRectGetWidth(self.view.frame) * [self.arrayImages count], ImageHeight)];
     [self.view addSubview:_scrollView];

     _pageControl = [[UIPageControl alloc] initWithFrame:CGRectMake(, self.scrollView.frame.size.height - , , )];
     [_pageControl setBackgroundColor:[UIColor blackColor]];

     _pageControl.currentPage = ;
     _pageControl.numberOfPages = [self.arrayImages count];
     [_pageControl addTarget:self action:@selector(chagePage:) forControlEvents:UIControlEventValueChanged];
     [self.view addSubview:_pageControl];

     _viewController = [[NSMutableArray alloc] init];

     ; i < [self.arrayImages count]; i++) {
         [_viewController addObject:[NSNull null]];
     }

     _timer = [NSTimer scheduledTimerWithTimeInterval: target:self selector:@selector(scrollPages) userInfo:nil repeats:YES];

     [self loadScrollViewPage:];
     [self loadScrollViewPage:];
     [self loadScrollViewPage:];
     [self loadScrollViewPage:];
 }

下面是实现loadScrollViewPage的方法，因为这里用到了定时器的自动滚动，所以在viewDidLoad里面把所有的图片都自动装载进去了。

 -(void)loadScrollViewPage:(NSInteger)page
 {
     if (page >= self.arrayImages.count) {
         return;
     }

     UIViewController *imageViewController = [self.viewController objectAtIndex:page];
     if ((NSNull *)imageViewController == [NSNull null])
     {
         imageViewController = [[UIViewController alloc] init];
         [self.viewController replaceObjectAtIndex:page withObject:imageViewController];
     }

     if (imageViewController.view.superview == nil) {
         CGRect frame = self.scrollView.frame;
         frame.origin.x = CGRectGetWidth(frame) * page;
         frame.origin.y = ;
         imageViewController.view.frame = frame;

         //[self addChildViewController:imageViewController];
         [self.scrollView addSubview:imageViewController.view];
         [imageViewController didMoveToParentViewController:self];

         [imageViewController.view setBackgroundColor:[UIColor colorWithPatternImage:(UIImage *)[self.arrayImages objectAtIndex:page]]];
     }
 }

接下来的工作就是要实现UIScrollView的委托方法，实现横向滚动来切换到下一图片，以及UIPageControl 切换图片的方法，先看看scrollViewDidEndDecelerating的方法声明吧。

 -(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
 {
     CGFloat pageWidth = CGRectGetWidth(self.scrollView.frame);
     NSInteger page = floor((self.scrollView.contentOffset.x -pageWidth/)/pageWidth) +;
     self.pageControl.currentPage = page;

     [self loadScrollViewPage:page-];
     [self loadScrollViewPage:page];
     [self loadScrollViewPage:page+];
 }

然后就是UIPageControl的changePage 方法。

 - (IBAction)changePage:(id)sender
 {
     NSInteger page = self.pageControl.currentPage;

     [self loadScrollViewPage:page - ];
     [self loadScrollViewPage:page];
     [self loadScrollViewPage:page + ];

     CGRect bounds = self.scrollView.bounds;
     bounds.origin.x = CGRectGetWidth(bounds) * page;
     bounds.origin.y = ;
     [self.scrollView scrollRectToVisible:bounds animated:YES];
 }

最后的任务就是要完成在viewDidLoad里面对NSTimer声明的切换图片的方法。

 -(void)scrollPages{
     ++self.pageControl.currentPage;
     CGFloat pageWidth = CGRectGetWidth(self.scrollView.frame);
     if (isFromStart) {
         [self.scrollView setContentOffset:CGPointMake(, ) animated:YES];
         self.pageControl.currentPage = ;
     }
     else
     {
         [self.scrollView setContentOffset:CGPointMake(pageWidth*self.pageControl.currentPage, self.scrollView.bounds.origin.y)];

     }
     ) {
         isFromStart = YES;
     }
     else
     {
         isFromStart = NO;
     }
 }

以上就是实现效果图中所需要的代码了。制作这个demo的时候参照了SDK里面的PageControl的代码，然后自己动手加工完成的。

参考文献：

https://developer.apple.com/library/ios/#samplecode/PageControl/Introduction/Intro.html