MG--UIScrollView无限滚动

UIScrollView无限滚动的图解：

UIScrollView无限滚动的思路：就是每一次滑动之后显示图片都是最中间的那张图片，每次滑动都要改变图片下标的索引，第一张和最后一张要做特殊判断

---

UIScrollView无限滚动的代码：

.h文件

//  XMGInfiniteScrollView.h
//  无限滚动-UIScrollView
//  Created by 1 on 14/12/30.
//  Copyright © 2014年 xiaoming. All rights reserved.

#import 
@interface XMGInfiniteScrollView : UIView
#pragma mark - 给外界提供接口
@property (nonatomic, strong) NSArray *imageNames;  /** 本地图片名 */
@property (nonatomic, strong) NSArray *imageNames;   /** 远程图片URL */
//@property (nonatomic, strong) NSArray *images;  /** 图片 */
@end

.m文件

//  XMGInfiniteScrollView.m
//  无限滚动-UIScrollView
//  Created by 1 on 14/12/30.
//  Copyright © 2014年 xiaoming. All rights reserved.

#import "XMGInfiniteScrollView.h"
@interface XMGInfiniteScrollView()

@property (nonatomic, weak) UIScrollView *scrollView;
@property (nonatomic, weak) UIPageControl *pageControl;
@property (nonatomic, weak) NSTimer *timer;
@end
@implementation XMGInfiniteScrollView
static NSUInteger const XMGImageViewCount = 3;
#pragma mark - 初始化方法
- (instancetype)initWithFrame:(CGRect)frame
{
  if (self = [super initWithFrame:frame]) { 
  // 创建并添加scrollView对象
  UIScrollView *scrollView = [[UIScrollView alloc] init];
  scrollView.backgroundColor = [UIColor redColor];
  scrollView.showsVerticalScrollIndicator = NO; // 隐藏垂直滚动条
  scrollView.showsHorizontalScrollIndicator = NO;  // 隐藏水平滚动条
  scrollView.pagingEnabled = YES;  // 分页
  scrollView.delegate = self; // 代理
  [self addSubview:scrollView];
  self.scrollView = scrollView;
  self.scrollView.bounces = NO;
  // 创建3个UIImageView对象
  for (NSUInteger i = 0; i < XMGImageViewCount; i++) {
    UIImageView *imageView = [[UIImageView alloc] init];
    [scrollView addSubview:imageView];
  }
    // 创建pageControl对象
    UIPageControl *pageControl = [[UIPageControl alloc] init];
    pageControl.backgroundColor = [UIColor blueColor];
    [self addSubview:pageControl];
    self.pageControl = pageControl;
    // 开启定时器
    [self startTimer];
  }
   return self;
}
- (void)layoutSubviews
{
  [super layoutSubviews];
  // scrollView
  self.scrollView.frame = self.bounds;
  // 设置pageControl的frame
  CGFloat pageControlW = 100;
  CGFloat pageControlH = 30;
  CGFloat pageControlX = self.bounds.size.width - pageControlW;
  CGFloat pageControlY = self.bounds.size.height - pageControlH;
  self.pageControl.frame = CGRectMake(pageControlX,  pageControlY, pageControlW, pageControlH);
 // 设置3个UIImageView的frame 
 CGFloat imageW = self.scrollView.frame.size.width;
 CGFloat imageH = self.scrollView.frame.size.height;
 for (NSUInteger i = 0; i < XMGImageViewCount; i++) {
   UIImageView *imageView = self.scrollView.subviews[i];
   CGFloat imageX = i * imageW; 
   CGFloat imageY = 0;
   imageView.frame = CGRectMake(imageX, imageY, imageW, imageH);
   imageView.backgroundColor = [UIColor   colorWithRed:arc4random_uniform(255)/255.0 green:arc4random_uniform(255)/255.0   blue:arc4random_uniform(255)/255.0 alpha:1.0];
}
self.scrollView.contentSize = CGSizeMake(XMGImageViewCount * imageW, 0);
// 更新UIImageView内容
   [self updateContent];
}
#pragma mark - 属性setter
- (void)setImageNames:(NSArray *)imageNames
{
  _imageNames = imageNames;
  // 设置总页码
  self.pageControl.numberOfPages = imageNames.count;
}```

#核心代码开头

pragma mark - 其他方法

• (void)updateContent
  {
  // 1.从左到右重新设置每一个UIImageView的图片
  for (NSUInteger i = 0; i < XMGImageViewCount; i++) {
  UIImageView *imageView = self.scrollView.subviews[i];
  // 求出i位置imageView对应的图片索引
  NSInteger imageIndex = 0; // 这里的imageIndex不能用NSUInteger
  if (i == 0) { // 当前页码 - 1
  imageIndex = self.pageControl.currentPage - 1;
  } else if (i == 2) { // 当前页码 + 1
  imageIndex = self.pageControl.currentPage + 1;
  } else { // // 当前页码
  imageIndex = self.pageControl.currentPage;
  }
  // 判断越界
  if (imageIndex == -1) { // 最后一张图片
  imageIndex = self.imageNames.count - 1;
  } else if (imageIndex == self.imageNames.count) { // 最前面那张
  imageIndex = 0;
  }
  imageView.image = [UIImage imageNamed:self.imageNames[imageIndex]];
  // 绑定图片索引到UIImageView的tag
  imageView.tag = imageIndex;
  }
  // 2.重置UIScrollView的contentOffset.width == 1倍宽度
  self.scrollView.contentOffset = CGPointMake(self.scrollView.frame.size.width, 0);
  }
  核心代码结束

pragma mark -

/****
*** 只要scrollView滚动，就会调用这个方法
*/

• (void)scrollViewDidScroll:(UIScrollView *)scrollView
  {
  // imageView的x 和 scrollView偏移量x 的最小差值
  CGFloat minDelta = MAXFLOAT;
  // 找出显示在最中间的图片索引
  NSInteger centerImageIndex = 0;
  for (NSUInteger i = 0; i < XMGImageViewCount; i++) {
  UIImageView *imageView = self.scrollView.subviews[i];
  // ABS : 取得绝对值
  CGFloat delta = ABS(imageView.frame.origin.x - self.scrollView.contentOffset.x);
  if (delta < minDelta) {
  minDelta = delta;
  centerImageIndex = imageView.tag;
  }
  }
  // 设置页码
  self.pageControl.currentPage = centerImageIndex;
  }

/**

• 滚动完毕后调用（前提：手松开后继续滚动）
  */

• (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
  {
  [self updateContent];
  }

/**

• 当用户即将开始拖拽的时候调用
  */

• (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
  {
  [self stopTimer];
  }

/**

• 当用户即将结束拖拽的时候调用
  */

• (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
  {
  [self startTimer];
  }

pragma mark - 定时器处理

// 开启定时器

• (void)startTimer
  {
  self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(nextPage) userInfo:nil repeats:YES];
  [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
  }
  // 停止定时器
• (void)stopTimer
  {
  [self.timer invalidate];
  self.timer = nil;
  }
  // 显示下一页
• (void)nextPage
  {
  [UIView animateWithDuration:0.25 animations:^{
  self.scrollView.contentOffset = CGPointMake(2 * self.scrollView.frame.size.width, 0);
  } completion:^(BOOL finished) {
  [self updateContent];
  }];
  }
  @end```

运行效果图：

UIScrollView的无限循环滚动（封装）UIScrollView的无限循环滚动（封装）来MG明明就是你新浪博客