[iOS]通过UIScrollView和UIPageControl实现滑动切换的效果

UIPageControl是自带的控件，可以查看官方文档，下载官方示例学习。
如果对Xcode自带的文档不熟悉可以参见：苹果Xcode帮助文档阅读指南
接下来是我学习笔记，使用Storyboard实现滑动切换的效果。

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新建一个项目，拖上一个UIScrollView和UIPageControl，并且建立关联：



新建一个ContentViewController，作为页面切换的内容视图：



也就是说，当滑动屏幕切换的时候，其实就是多个ContentViewController在切换。

基本结构是：



在主页面，我们首先初始化一些设置：
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.

// 初始化page control的内容
_contentList = [NSArray arrayWithObjects:@"1",@"2",@"3",@"4", nil];

// 一共有多少页
NSUInteger numberPages = self.contentList.count;

// 存储所有的controller
NSMutableArray *controllers = [[NSMutableArray alloc] init];
for (NSUInteger i = 0; i < numberPages; i++)
{
[controllers addObject:[NSNull null]];
}
self.viewControllers = controllers;

// 一个页面的宽度就是scrollview的宽度
self.myScrollView.pagingEnabled = YES; // 自动滚动到subview的边界
self.myScrollView.contentSize =
CGSizeMake(CGRectGetWidth(self.myScrollView.frame) * numberPages, CGRectGetHeight(self.myScrollView.frame));
self.myScrollView.showsHorizontalScrollIndicator = NO;
self.myScrollView.showsVerticalScrollIndicator = NO;
self.myScrollView.scrollsToTop = NO;
self.myScrollView.delegate = self;

_numberOfPages = numberPages;
_myPageControl.numberOfPages = numberPages;
_currentPage = 0;

[self loadScrollViewWithPage:0];
[self loadScrollViewWithPage:1];

}

接下来，我们需要一个函数，来加载ContentView页面上的元素：
// 加载ScrollView中的不同SubViewController
- (void)loadScrollViewWithPage:(NSUInteger)page
{
if (page >= self.contentList.count)
return;

// replace the placeholder if necessary
LContentViewController *controller = [self.viewControllers objectAtIndex:page];
if ((NSNull *)controller == [NSNull null])
{
controller = [[LContentViewController alloc] init];
[self.viewControllers replaceObjectAtIndex:page withObject:controller];
}

// add the controller's view to the scroll view
if (controller.view.superview == nil)
{
CGRect frame = self.myScrollView.frame;
frame.origin.x = CGRectGetWidth(frame) * page;
frame.origin.y = 0;
controller.view.frame = frame;
[controller setLabel:[_contentList objectAtIndex:page]];
[self.myScrollView addSubview:controller.view];
}
}

然后先来处理一下PageControl的切换事件：- (void)gotoPage:(BOOL)animated
{
NSInteger page = self.myPageControl.currentPage;

// load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
[self loadScrollViewWithPage:page - 1];
[self loadScrollViewWithPage:page];
[self loadScrollViewWithPage:page + 1];

// update the scroll view to the appropriate page
CGRect bounds = self.myScrollView.bounds;
bounds.origin.x = CGRectGetWidth(bounds) * page;
bounds.origin.y = 0;
[self.myScrollView scrollRectToVisible:bounds animated:animated];
}

// page control 选项修改监听
- (IBAction)changePage:(id)sender
{
[self gotoPage:YES]; // YES = animate
}
滑动ScrollView的事件监听：
// 滑动结束的事件监听
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
// switch the indicator when more than 50% of the previous/next page is visible
CGFloat pageWidth = CGRectGetWidth(self.myScrollView.frame);
NSUInteger page = floor((self.myScrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
self.myPageControl.currentPage = page;
NSLog(@"当前页面 = %d",page);
// a possible optimization would be to unload the views+controllers which are no longer visible

[self loadScrollViewWithPage:page - 1];
[self loadScrollViewWithPage:page];
[self loadScrollViewWithPage:page + 1];
}