iOS 实现无缝滚动

头文件：

#import @class ArticleViewController;@interface ArticleScrollViewController : UIViewController  {        //不使用数组，看起来更明了，为了节省内存同时还要看起来无缝，3个view最好ArticleViewController*article1;ArticleViewController*article2;ArticleViewController*article3;}@end

实现：

#import "ArticleScrollViewController.h"#import "ArticleViewController.h"#import "ViewSwitcher.h"@implementation ArticleScrollViewController// vieDidLoad函数不重要，只要初始化了三个view并放在uiscrollview里面，正确设定uiscrollview的content size就行了- (void)viewDidLoad {    [super viewDidLoad];    UIScrollView *scrollView = (UIScrollView *)self.view;    scrollView.contentSize = CGSizeMake(self.view.frame.size.width*3, self.view.frame.size.height);    CGRect frame = self.view.frame;    frame.origin.y = 0.0f;    NSInteger article2Index = [ViewSwitcher getInstance].currentArticleIndex;    NSInteger article1Index = article2Index - 1;    article1Index = article1Index < 0 ? [ViewSwitcher getInstance].articleCount - 1 : article1Index;    article1Index = article1Index >= [ViewSwitcher getInstance].articleCount ? 0 : article1Index;    NSInteger article3Index = article2Index + 1;    article3Index = article3Index < 0 ? [ViewSwitcher getInstance].articleCount - 1 : article3Index;    article3Index = article3Index >= [ViewSwitcher getInstance].articleCount ? 0 : article3Index;    article1 = [[ArticleViewController alloc] initWithArticleIndex:article1Index];    [article1.view setFrame:frame];    article2 = [[ArticleViewController alloc] initWithArticleIndex:article2Index];    frame.origin.x += self.view.frame.size.width;    [article2.view setFrame:frame];    article3 = [[ArticleViewController alloc] initWithArticleIndex:article3Index];    frame.origin.x += self.view.frame.size.width;    [article3.view setFrame:frame];    [scrollView addSubview:article1.view];    [scrollView addSubview:article2.view];    [scrollView addSubview:article3.view];    CGPoint p = CGPointZero;    p.x = scrollView.frame.size.width;    [scrollView setContentOffset:p animated:NO];    [article2 reloadData];}#pragma mark -#pragma mark UIScrollViewDelegate#define SET_FRAME(ARTICLEX) x = ARTICLEX.view.frame.origin.x + increase;\                            if(x < 0) x = pageWidth * 2;\                            if(x > pageWidth * 2) x = 0.0f;\                            [ARTICLEX.view setFrame:CGRectMake(x, \                                ARTICLEX.view.frame.origin.y,\                                ARTICLEX.view.frame.size.width,\                                ARTICLEX.view.frame.size.height)]//将三个view都向右移动，并更新三个指针的指向，article2永远指向当前显示的view，article1是左边的，article3是右边的- (void)allArticlesMoveRight:(CGFloat)pageWidth {    //上一篇    article3.articleIndex = article1.articleIndex - 1;    if (article3.articleIndex < 0) {        article3.articleIndex = [ViewSwitcher getInstance].articleCount - 1;    }    [article1 reloadData];    ArticleViewController *tmpArticleViewController = article3;    article3 = article2;    article2 = article1;    article1 = tmpArticleViewController;    float increase = pageWidth;    CGFloat x = 0.0f;    SET_FRAME(article3);    SET_FRAME(article1);    SET_FRAME(article2);}- (void)allArticlesMoveLeft:(CGFloat)pageWidth {    article1.articleIndex = article3.articleIndex + 1;    if (article1.articleIndex >= [ViewSwitcher getInstance].articleCount) {        article1.articleIndex = 0;    }    [article3 reloadData];//[article2 resetView];[article3 resetView];    ArticleViewController *tmpArticleViewController = article1;    article1 = article2;    article2 = article3;    article3 = tmpArticleViewController;    float increase = -pageWidth;    CGFloat x = 0.0f;    SET_FRAME(article2);    SET_FRAME(article3);    SET_FRAME(article1);}/* 循环滚动 每次滚动后都将scrollview的offset设置为中间的一页 若本次滚动是向前一页滚动，则把三页都向后放置，最后一页放到开头 若本次滚动是向后一页滚动，则把三页都向前放置，第一页放到末尾 */- (void)scrollViewDidEndDecelerating:(UIScrollView *)theScrollView{    CGFloat pageWidth = theScrollView.frame.size.width;    // 0 1 2    int page = floor((theScrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;    if(page == 1) {        //用户拖动了，但是滚动事件没有生效        return;    } else if (page == 0) {        [self allArticlesMoveRight:pageWidth];    } else {        [self allArticlesMoveLeft:pageWidth];    }    CGPoint p = CGPointZero;    p.x = pageWidth;    [theScrollView setContentOffset:p animated:NO];    [article1 resetView];    [article3 resetView];}#pragma mark -#pragma mark dealloc- (void)didReceiveMemoryWarning {    // Releases the view if it doesn't have a superview.    [super didReceiveMemoryWarning];    // Release any cached data, images, etc. that aren't in use.}- (void)viewDidUnload {    [super viewDidUnload];    // Release any retained subviews of the main view.    // e.g. self.myOutlet = nil;    [article1    release];article1 = nil;    [article2    release];article2 = nil;    [article3    release];article3 = nil;}- (void)dealloc {    [article1    release];    [article2    release];    [article3    release];    [super dealloc];}@end

这里的雕虫小技主要在于：

以手指向右拖动为例，【屏幕】指的是scorllview的显示区域

  article1 article2 article3           【屏幕】

  拖动以后成这样：

 article1 article2 article3【屏幕】

将article3放到第一个去（设定article3的frame），这是屏幕还显示的是article1的内容

article3 article1 article2【屏幕】

将屏幕移到中间：使用setContentOffset，禁用动画，这样骗过人眼

article3 article1 article2          【屏幕】

最后更新指针顺序：

article1 article2 article3          【屏幕】

无缝循环实现了。