在使用某宝或某东购物的时候,我们会在其首页看到一个可以滑动的版块,这个版块的实现就是一个UIScrollView.在我们使用UIScrollView的时候会发现,滑动到最后的时候,UIScrollView不能像上面说的版块那样又回到最初的地方.基于此,做了一个小Demo来实现UIScrollView的无限循环滑动.
小小思路:UIScrollView具有分页属性,要实现UIScrollView的无限循环滑动,我们不能生硬暴力的给一个数组按规律的,无限的添加图片,这样手机内存还不爆炸 0.0 , 如何用最少的页面实现无限循环呢? 三个,其实只需要三个页面就可以实现UIScrollView的无限循环滑动.左丶中丶右 三个页面.刚进入程序时,左边放最后一张图片,中间第一张图片,右边放第二张.向左滑动一张图片,左边变成了第一张图片,中间是第二张,右边则变成了第三张图片.依此便可实现UIScrollView的无限循环滑动了.
Demo 如下 :
.h文件
声明一个数组来接收外部传入的图片
@interface MyScrollView: UIView <UIScrollViewDelegate>
@property(nonatomic, strong)NSArray *dataArr;
@end
.m文件
实现无线循环滑动
#define kPageCtrlHeight 37 //UIPageControl的高度
@interface MyScrollView ()
{
UIImageView *leftView;
UIImageView *centerView;
UIImageView *rightView;
UIScrollView *scrollView;
UIPageControl *pageCtrl; // 页面控制器 ...
NSInteger currentPageNumber;
}
@end
@implementation MyScrollView
/*----------------始终只有左,中,右3个imgView,将数据源加入到这3个imgView中显示--------------------------*/
- (instancetype)init
{
return [self initWithFrame:[UIScreen mainScreen].bounds];
}
- (instancetype)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self createUI:frame];
}
return self;
}
-(void)createUI:(CGRect)frame
{
scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, frame.size.width, frame.size.height - kPageCtrlHeight)];
scrollView.delegate = self;
scrollView.pagingEnabled = YES;
scrollView.showsHorizontalScrollIndicator = NO;
scrollView.showsVerticalScrollIndicator = NO;
pageCtrl = [[UIPageControl alloc] initWithFrame:CGRectMake(0, frame.size.height - kPageCtrlHeight, frame.size.width, kPageCtrlHeight)];
pageCtrl.backgroundColor = [UIColor lightGrayColor];
[self addSubview:scrollView];
[self addSubview:pageCtrl];
leftView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
centerView = [[UIImageView alloc] initWithFrame:CGRectMake(scrollView.frame.size.width, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
rightView = [[UIImageView alloc] initWithFrame:CGRectMake(scrollView.frame.size.width*2, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
[scrollView addSubview:leftView];
[scrollView addSubview:centerView];
[scrollView addSubview:rightView];
}
-(void)setDataArr:(NSArray *)dataArr
{
if (![dataArr isKindOfClass:[NSArray class]] || dataArr.count == 0) {
return;
}
_dataArr = dataArr;
[self setInitProperty];
}
-(void)setInitProperty
{
pageCtrl.numberOfPages = _dataArr.count; //总页码
//内容
scrollView.contentSize = CGSizeMake(_dataArr.count * scrollView.frame.size.width, scrollView.frame.size.height);
[scrollView setContentOffset:CGPointMake(scrollView.frame.size.width, 0)];//偏移位置,第一页
currentPageNumber = 0;
[self loadPageContent];
}
-(void)loadPageContent
{
centerView.image = [UIImage imageNamed:_dataArr[currentPageNumber]];
NSInteger leftImgIndex = (currentPageNumber - 1 + _dataArr.count) % _dataArr.count;
leftView.image = [UIImage imageNamed:_dataArr[leftImgIndex]];
NSInteger rightImgIndex = (currentPageNumber + 1) % _dataArr.count;
rightView.image = [UIImage imageNamed:_dataArr[rightImgIndex]];
pageCtrl.currentPage = currentPageNumber;
}
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView_
{
if (scrollView.contentOffset.x > scrollView.bounds.size.width) { //向左滑动
currentPageNumber = (currentPageNumber + 1) % _dataArr.count;
}else if (scrollView.contentOffset.x < scrollView.bounds.size.width){ //向右滑动
currentPageNumber = (currentPageNumber - 1 + _dataArr.count) % _dataArr.count;
}
[self loadPageContent];
scrollView.contentOffset = CGPointMake(scrollView.bounds.size.width, 0);
}
@end
ViewController.m 文件:
对myScrollView初始化并
调用myScrollView中dataArr setter方法即可。
123.gif
