最近在准备毕业论文和毕业设计的事情，也是比较忙，许久未写博客了。之前一直想写一个自己的无限轮播，于是乎写出来和大家分享一下。

思路

总体思路很简单，重写了个scrollview。里面设置三个imageview，显示的是中间那个imageView的图像。当滚动结束后，把当前显示的imageView的image转给中间的imageView，并且设置好两边的imageView。
设置了两个style，一个是给string，本地图片，一个是传url，结合SDwebImage，显示网络图片。

typedef NS_ENUM(NSInteger, LpScrollViewStyle){
LpSCrollVIewUrlStyle ,
LpSCrollVIewStringStyle};

初始化三个imageView，设置好位置和大小（用懒加载的方式）。

- (UIImageView *)leftImageView{
if (_leftImageView == nil) {
    _leftImageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, SCREENWIDTH, IMAGEHEIGHT)];
}
return _leftImageView;
}
- (UIImageView *)midImageView{
if (_midImageView == nil) {
    _midImageView = [[UIImageView alloc] initWithFrame:CGRectMake(SCREENWIDTH, 0, SCREENWIDTH, IMAGEHEIGHT)];
}
return _midImageView;
}
- (UIImageView *)rightImageView{
if (_rightImageView == nil) {
    _rightImageView = [[UIImageView alloc] initWithFrame:CGRectMake(SCREENWIDTH * 2, 0, SCREENWIDTH, IMAGEHEIGHT)];
}
return _rightImageView;
}

根据传入的数组初始化每个imageView的image。
- (void)set_imageWithString{
NSInteger count = self.imageArray.count;
if (count == 1) {
self.midImageView.image = [UIImage imageNamed:self.imageArray[0]];
self.leftImageView.image = [UIImage imageNamed:self.imageArray[0]];
self.rightImageView.image = [UIImage imageNamed:self.imageArray[0]];
}else if(count == 2){
self.midImageView.image = [UIImage imageNamed:self.imageArray[0]];
self.leftImageView.image = [UIImage imageNamed:self.imageArray[1]];
self.rightImageView.image = [UIImage imageNamed:self.imageArray[1]];
}else{
self.midImageView.image = [UIImage imageNamed:self.imageArray[0]];
self.leftImageView.image = [UIImage imageNamed:self.imageArray[count - 1]];
self.rightImageView.image = [UIImage imageNamed:self.imageArray[1]];
}
}
- (void)set_imageWithUrl{
NSInteger count = self.imageArray.count;
if (count == 1) {
[self.midImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[0]] placeholderImage:[UIImage imageNamed:@""]];
[self.leftImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[0]] placeholderImage:[UIImage imageNamed:@""]];
[self.rightImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[0]] placeholderImage:[UIImage imageNamed:@""]];
}else if(count == 2){
[self.midImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[0]] placeholderImage:[UIImage imageNamed:@""]];
[self.leftImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[1]] placeholderImage:[UIImage imageNamed:@""]];
[self.rightImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[1]] placeholderImage:[UIImage imageNamed:@""]];
}else{
[self.midImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[0]] placeholderImage:[UIImage imageNamed:@""]];
[self.leftImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[count - 1]] placeholderImage:[UIImage imageNamed:@""]];
[self.rightImageView sd_setImageWithURL:[NSURL URLWithString:self.imageArray[1]] placeholderImage:[UIImage imageNamed:@""]];
}

}

设置好定时器，用于计时作用，由于有时候人为的拖动需要重置定时器，所以设置了isTimeUp布尔类型的成员变量对他进行控制。
- (void)set_timer{
if (self.imageArray.count != 1) {
self.timer = [NSTimer scheduledTimerWithTimeInterval:changeImageTime target:self selector:@selector(imageViewMoved) userInfo:nil repeats:YES];
isTimeUp = NO;
}
}

- (void)imageViewMoved{
[self setContentOffset:CGPointMake(SCREENWIDTH * 2, 0) animated:YES];
isTimeUp = YES;
[NSTimer scheduledTimerWithTimeInterval:0.4f target:self selector:@selector(scrollViewDidEndDecelerating:) userInfo:nil repeats:NO];
}

定时器方法调用的是UIScrollViewDelegate里的方法，当滑动结束后，会自动去更新imageView显示的内容，并且把scrollview的contentoffset设置到中间的imageView

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
if (self.contentOffset.x == SCREENWIDTH * 2) {
    if (index == self.imageArray.count - 1) {
        index = 0;
    }else{
        index = index + 1;
    }
}else{
    if (index == 0) {
        index = self.imageArray.count - 1;
    }else{
        index = index - 1;
    }
    }

self.pageControl.currentPage = index % 3;

if (self.lpStyle == LpSCrollVIewStringStyle) {
    [self string_Decelerating];
}else{
    [self url_decelerating];
}

self.contentOffset = CGPointMake(SCREENWIDTH, 0);

if (!isTimeUp) {
    [self.timer setFireDate:[NSDate dateWithTimeIntervalSinceNow:changeImageTime]];
}
isTimeUp = NO;
}

- (void)string_Decelerating{
NSInteger count = self.imageArray.count;
if (index == 0) {
    _leftImageView.image = [UIImage imageNamed:_imageArray[(count - 1)%count]];
    _midImageView.image = [UIImage imageNamed:_imageArray[(index )%count]];
    _rightImageView.image = [UIImage imageNamed:_imageArray[(index + 1)%count]];
}else{
    _leftImageView.image = [UIImage imageNamed:_imageArray[(index - 1)%count]];
    _midImageView.image = [UIImage imageNamed:_imageArray[(index )%count]];
    _rightImageView.image = [UIImage imageNamed:_imageArray[(index + 1)%count]];
}
}

- (void)url_decelerating{
NSInteger count = self.imageArray.count;
if (index == 0) {
    [_leftImageView sd_setImageWithURL:self.imageArray[(count-1)%count]];
    [_midImageView sd_setImageWithURL:self.imageArray[index%count]];
    [_rightImageView sd_setImageWithURL:self.imageArray[(index+1)%count]];
}else{
    [_leftImageView sd_setImageWithURL:self.imageArray[(index-1)%count]];
    [_midImageView sd_setImageWithURL:self.imageArray[index%count]];
    [_rightImageView sd_setImageWithURL:self.imageArray[(index+1)%count]];
}
}

结束语

非常感谢各位的观看，欢迎交流，附上demo地址：https://github.com/ioscick/LpScrollview-Demo