簡介
在現在的一些App中常常見到圖片輪播器，一般用於展示廣告、新聞等數據，在iOS內並沒有現成的控件直接實現這種功能，但是通過UIScrollView的允許分頁設置，可以實現滾動輪播的功能。
輪播原理
UIScrollView對象有pagingEnable成員，如果設置爲YES，那麼每一個scrollView尺寸這麼大的區域就會被當作一頁，在滾動時會根據滾動的比例自動計算應該切換到哪一頁。
無限滾動原理
要實現無限滾動，需要額外的兩張圖片，假設我們的圖片有五張，存在images數組中，那麼我們在將圖片插入到scrollView中時，在第一張圖片前面插入一個最後一張圖片作爲輔助圖片，在最後一張後面插入一個第一張圖片作爲輔助圖片。這樣，當滾動到第一張前面一張時，在頁面切換結束後無動畫的切換scrollView的偏移量爲最後一張圖片（不包含最後一張後面的第一張那個輔助圖片），這樣就實現了由輔助圖片到真實圖片的過渡，之所以設置輔助圖片是爲了在滾動中看到那個真實圖片。同理，當滾動到最後一張的後面一張時，我們吧scrollView的偏移量設置爲第一張圖片即可。
具體的代碼實現
這個代碼是在開發一個項目中所寫的，已經封裝稱一個View，只需要調用initWithFrame指定輪播器尺寸，然後通過設置images成員的值即可實現無限滾動的輪播。
// .h
//
// ESPicPageView.h
// 享技
//
// Created by 11 on 11/30/15.
// Copyright © 2015 soulghost. All rights reserved.
//
#import <UIKit/UIKit.h>
@interface ESPicPageView : UIView
@property (nonatomic, strong) NSArray *images;
@end
// --------------------------------------------
// .m
//
// ESPicPageView.m
// 享技
//
// Created by 11 on 11/30/15.
// Copyright © 2015 soulghost. All rights reserved.
//
#import "ESPicPageView.h"
#import "UIImageView+WebCache.h"
@interface ESPicPageView () <UIScrollViewDelegate>
@property (nonatomic, weak) UIScrollView *scrollView;
@property (nonatomic, weak) UIPageControl *pageControl;
@property (nonatomic, assign) CGFloat imgW;
@property (nonatomic, assign) CGFloat imgH;
@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, strong) NSArray *imageViews;
@property (nonatomic, assign) NSInteger imageCount;
@end
@implementation ESPicPageView
- (instancetype)initWithFrame:(CGRect)frame{
if (self = [super initWithFrame:frame]) {
self.backgroundColor = [UIColor blueColor];
UIScrollView *scrollView = [[UIScrollView alloc] init];
self.scrollView = scrollView;
self.scrollView.delegate = self;
self.scrollView.pagingEnabled = YES;
self.scrollView.showsHorizontalScrollIndicator = NO;
self.scrollView.backgroundColor = [UIColor whiteColor];
[self addSubview:scrollView];
self.imgW = frame.size.width;
self.imgH = frame.size.height;
[self setNeedsLayout];
UIPageControl *pageControl = [[UIPageControl alloc] initWithFrame:CGRectMake(frame.size.width - 50, frame.size.height - 10, 0, 0)];
self.pageControl = pageControl;
self.pageControl.numberOfPages = 1;
[self addSubview:pageControl];
self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(nextImage) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}
return self;
}
- (void)nextImage{
NSInteger page = self.pageControl.currentPage;
page = self.pageControl.currentPage + 1;
CGPoint offset = CGPointMake((1 + page) * self.imgW, 0);
[self.scrollView setContentOffset:offset animated:YES];
}
- (void)setupImageViews{
for (int i = 0; i < self.images.count + 2; i++) {
UIImageView *imageView = [[UIImageView alloc] init];
CGFloat imageX = i * self.imgW;
CGFloat imageY = 0;
CGFloat imageW = self.imgW;
CGFloat imageH = self.imgH;
imageView.frame = CGRectMake(imageX, imageY, imageW,imageH);
[self.scrollView insertSubview:imageView atIndex:0];
}
}
- (NSArray *)imageViews{
if (_imageViews == nil) {
NSMutableArray *arr = [NSMutableArray array];
for (int i = 0; i < self.images.count + 2; i++) {
UIImageView *imageView = [[UIImageView alloc] init];
CGFloat imageX = i * self.imgW;
CGFloat imageY = 0;
CGFloat imageW = self.imgW;
CGFloat imageH = self.imgH;
imageView.frame = CGRectMake(imageX, imageY, imageW,imageH);
[self.scrollView insertSubview:imageView atIndex:0];
[arr addObject:imageView];
}
_imageViews = arr;
}
return _imageViews;
}
- (void)setImages:(NSArray *)images{
_images = images;
self.imageCount = images.count;
self.pageControl.numberOfPages = self.imageCount;
[self addPics];
}
- (void)addPics{
for (int i = 0; i < self.images.count + 2; i++) {
UIImageView *imageView = self.imageViews[i];
if (i == 0) {
imageView.image = [self.images lastObject];
}else if(i == self.images.count + 1){
imageView.image = [self.images firstObject];
}else{
imageView.image = self.images[i - 1];
}
}
}
- (void)layoutSubviews{
[super layoutSubviews];
self.scrollView.frame = self.bounds;
self.scrollView.contentSize = CGSizeMake((self.imageCount + 2) * self.imgW, 0);
[self.scrollView setContentOffset:CGPointMake(self.imgW, 0) animated:NO];
}
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
[self.timer invalidate];
self.timer = nil;
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(nextImage) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop ] addTimer:self.timer forMode:NSRunLoopCommonModes];
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
if (scrollView.contentOffset.x == self.imgW * (self.imageCount + 1)) {
[self.scrollView setContentOffset:CGPointMake(self.imgW, 0) animated:NO];
}else if(scrollView.contentOffset.x == 0){
[self.scrollView setContentOffset:CGPointMake(self.imgW * (self.imageCount), 0) animated:NO];
}
self.pageControl.currentPage = (self.scrollView.contentOffset.x + self.imgW * 0.5f) / self.imgW - 1;
}
@end