UIScrollView的无限左滑轮播一点也不难

UIScrollView的轮播在如今的app中用得十分广泛，最初实现的时候方式比较拙劣，滚动到最后一个视图时再返回到第一个看起来非常的不连贯。

今天查询UIScrollView轮播资料，总结两种比较喜欢也易于理解的方法：

1、UIScrollView显示的子视图左右各放一个多出来的子视图，如本来有A/B/C三张图片，在A前面放一个ImageView显示C，在C后天放一个ImageView显示A，即C/A/B/C/A。

初始化ScrollView的时候，contentoffset 从A开始，然后 setContentOffset:offSetanimated:YES 依次轮播，当播放到C之后，跳转到A后，在

- (void)scrollViewDidScroll:(UIScrollView *)scrollView 中替换其contentoffset为第一个A的contentoffset。

代码如下：

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(10, 0, 300, 300)];
    _scrollView.frame = CGRectMake(10, 0, 300, 300);
    _scrollView.contentSize = CGSizeMake(300*5, 300);
    _scrollView.contentOffset = CGPointMake(300, 0);
    _scrollView.delegate = self;
    
    [self.view addSubview:_scrollView];
    
    UIImageView *imageView1 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 300, 300)];
    imageView1.image = [UIImage imageNamed:@"3.jpg"];
    [_scrollView addSubview:imageView1];
    
    UIImageView *imageView2 = [[UIImageView alloc] initWithFrame:CGRectMake(300, 0, 300, 300)];
    imageView2.image = [UIImage imageNamed:@"1.jpg"];
    [_scrollView addSubview:imageView2];
    
    UIImageView *imageView3 = [[UIImageView alloc] initWithFrame:CGRectMake(300*2, 0, 300, 300)];
    imageView3.image = [UIImage imageNamed:@"2.jpg"];
    [_scrollView addSubview:imageView3];
 
    UIImageView *imageView4 = [[UIImageView alloc] initWithFrame:CGRectMake(300*3, 0, 300, 300)];
    imageView4.image = [UIImage imageNamed:@"3.jpg"];
    [_scrollView addSubview:imageView4];
    
    UIImageView *imageView5 = [[UIImageView alloc] initWithFrame:CGRectMake(300*4, 0, 300, 300)];
    imageView5.image = [UIImage imageNamed:@"1.jpg"];
    [_scrollView addSubview:imageView5];
    
    //  设置时钟动画 定时器
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(update:) userInfo:nil repeats:YES];
    //  将定时器添加到主线程
    [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
}

- (void)update:(NSTimer *)timer{
    CGPoint offSet = self.scrollView.contentOffset;
    offSet.x += 300;
    [self.scrollView setContentOffset:offSet animated:YES];
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat X = self.scrollView.contentOffset.x;
    if (X == 0) {
        self.scrollView.contentOffset = CGPointMake(300*3, 0);
    }
    if (X == 300*4) {
         self.scrollView.contentOffset = CGPointMake(300, 0);
    }
}

这是方法1。里面的图片是随意在网上找的。

2、方法二是用固定的三个UIImageView控件，然后替换其图片来实现。

具体思路：先初始化三个图片控件，然后第一个控件放最后一张图，第二个图片放第一张图，第三个控件放第2张图。如轮播A/B/三个图片时，显示顺序是C/A/B。

后面的思路与上面类似，只不过要进行image替换。直接上代码：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIScrollView *scrollView =[[UIScrollView alloc] init];
    scrollView.frame = CGRectMake(0, 0, width, height);
    [self.view addSubview:scrollView];
    self.scrollView = scrollView;
    [self.scrollView setContentSize:CGSizeMake(width * 3, height)];
    //  设置隐藏横向条
    self.scrollView.showsHorizontalScrollIndicator = NO;
    //  设置自动分页
    self.scrollView.pagingEnabled = YES;
    //  设置代理
    self.scrollView.delegate = self;
    //  设置当前点
    self.scrollView.contentOffset = CGPointMake(width, 0);
    //  设置是否有边界
    self.scrollView.bounces = NO;
    
    
    //  初始化当前视图
    UIImageView *currentImageView =[[UIImageView alloc] init];
    currentImageView.image = [UIImage imageNamed:@"1.jpg"];
    [self.scrollView addSubview:currentImageView];
    self.currentImageView = currentImageView;
    self.currentImageView.frame = CGRectMake(width, 0, width, height);
    self.currentImageView.contentMode = UIViewContentModeScaleAspectFill;
    //  初始化下一个视图
    UIImageView *nextImageView = [[UIImageView alloc] init];
    nextImageView.image = [UIImage imageNamed:@"2.jpg"];
    [self.scrollView addSubview:nextImageView];
    self.nextImageView = nextImageView;
    self.nextImageView.frame = CGRectMake(width * 2, 0, width, height);
    self.nextImageView.contentMode = UIViewContentModeScaleAspectFill;
    //  初始化上一个视图
    UIImageView *preImageView =[[UIImageView alloc] init];
    preImageView.image = [UIImage imageNamed:@"3.jpg"];
    preImageView.frame = CGRectMake(0, 0, width, height);
    [self.scrollView addSubview:preImageView];
    self.preImageView = preImageView;
    self.preImageView.contentMode =UIViewContentModeScaleAspectFill;
    
    //  设置时钟动画 定时器
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(update:) userInfo:nil repeats:YES];
    //  将定时器添加到主线程
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
    
}

- (void)update:(NSTimer *)timer{
    //定时移动
    if (_isDragging == YES) {
        return ;
    }
    CGPoint offSet = self.scrollView.contentOffset;
    offSet.x +=offSet.x;
    [self.scrollView setContentOffset:offSet animated:YES];
     
}

// 开始拖动
- (void) scrollViewDidScroll:(UIScrollView *)scrollView{
    static int i =1; //   当前展示的是第几张图片
    float offset = self.scrollView.contentOffset.x;
    if (self.nextImageView.image == nil || self.preImageView.image == nil) {
        //  加载下一个视图
        NSString *imageName1 = [NSString stringWithFormat:@"%d.jpg",i == KOUNT ? 1:i +1];
        _nextImageView.image = [UIImage imageNamed:imageName1];
        // 加载上一个视图
        NSString *imageName2 = [NSString stringWithFormat:@"%d.jpg",i==1 ? KOUNT :i-1];
        _preImageView.image = [UIImage imageNamed:imageName2];
    }
    if(offset ==0){
        _currentImageView.image = _preImageView.image;
        scrollView.contentOffset = CGPointMake(width, 0);
        _preImageView.image = nil;
        if (i == 1) {
            i =KOUNT;
        } else{
            i-=1;
        }
    }
    if (offset == width * 2) {
        _currentImageView.image = _nextImageView.image;
        scrollView.contentOffset = CGPointMake(width, 0);
        _nextImageView.image = nil;
        if (i == KOUNT) {
            i  =1 ;
        }else{
            i +=1 ;
        }
    }
    
}

主要思路都是在滑动的动画执行完毕后，在用非动画方法移动的相同区域。