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(0, 0, 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(0, self.scrollView.frame.size.height - 20, 320, 20)];
    [_pageControl setBackgroundColor:[UIColor blackColor]];
    
    _pageControl.currentPage = 0;
    _pageControl.numberOfPages = [self.arrayImages count];
    [_pageControl addTarget:self action:@selector(chagePage:) forControlEvents:UIControlEventValueChanged];
    [self.view addSubview:_pageControl];
    
    _viewController = [[NSMutableArray alloc] init];
    
    for (NSInteger i = 0; i < [self.arrayImages count]; i++) {
        [_viewController addObject:[NSNull null]];
    }
    
    _timer = [NSTimer scheduledTimerWithTimeInterval:3 target:self selector:@selector(scrollPages) userInfo:nil repeats:YES];
    
    [self loadScrollViewPage:0];
    [self loadScrollViewPage:1];
    [self loadScrollViewPage:2];
    [self loadScrollViewPage:3];
}

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 = 0;
        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/2)/pageWidth) +1;
    self.pageControl.currentPage = page;
    
    [self loadScrollViewPage:page-1];
    [self loadScrollViewPage:page];
    [self loadScrollViewPage:page+1];
}

然后就是UIPageControl的changePage 方法。

- (IBAction)changePage:(id)sender
{
    NSInteger page = self.pageControl.currentPage;
    
    [self loadScrollViewPage:page - 1];
    [self loadScrollViewPage:page];
    [self loadScrollViewPage:page + 1];
    
    CGRect bounds = self.scrollView.bounds;
    bounds.origin.x = CGRectGetWidth(bounds) * page;
    bounds.origin.y = 0;
    [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(0, 0) animated:YES];
        self.pageControl.currentPage = 0;
    }
    else
    {
        [self.scrollView setContentOffset:CGPointMake(pageWidth*self.pageControl.currentPage, self.scrollView.bounds.origin.y)];
        
    }
    if (_pageControl.currentPage == _pageControl.numberOfPages - 1) {
        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