站在别人的肩膀上——iOS UIScrollView实现轮播

UIScrollView实现图片轮播有许多思路，当年刚做oc，找了许多demo学习，都不是太理想，一直想要一个高效精简的，后来偶然看到一位前辈的实现，觉得基本符合我的设想思路，于是整理使用至今。今天得空mark下，以备日后遗忘。

思路是只在UIScrollView上创建三个视图，通过轮播复用可以实现无限循环。

.h实现

@protocol JWHAdvertLoopViewDelegate;

@interface JWHAdvertLoopView : UIView 

@property (nonatomic, assign) id  delegate;
//当前页标记
@property (nonatomic, assign) NSInteger currentImageIndex;
//图像数组
@property (nonatomic, strong) NSMutableArray *imageAry;
/**
 *  开启自动翻页
 *
 *  @param shouldStart 开启自动翻页
 */
-(void)shouldAutoShow:(BOOL)shouldStart;
@end
@protocol JWHAdvertLoopViewDelegate 

@optional
//点击回调代理方法
- (void)didClickPage:(JWHAdvertLoopView *)view atIndex:(NSInteger)index;
@end

两个属性，一个控制自动翻页的方法加一个点击代理，基本够用了。

.m实现

先加几个私有的属性 以及核心视图UIScrollView

@interface JWHAdvertLoopView ()
{
    UIImageView *_leftView;
    UIImageView *_middleView;
    UIImageView *_rightView;
    
    CGFloat _viewWidth;
    CGFloat _viewHeight;
    
    NSTimer *_autoScrollTimer;
    
    UITapGestureRecognizer *_tap;
}
@property (nonatomic, readonly) UIScrollView *scrollView;

@end

@implementation JWHAdvertLoopView

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        
        _viewWidth = self.bounds.size.width;
        _viewHeight = self.bounds.size.height;
        
        //设置scrollview
        _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, _viewWidth, _viewHeight)];
        _scrollView.delegate = self;
        _scrollView.contentSize = CGSizeMake(_viewWidth * 3, _viewHeight);
        _scrollView.showsHorizontalScrollIndicator = NO;
        _scrollView.pagingEnabled = YES;
        _scrollView.delegate = self;
        _scrollView.contentOffset = CGPointMake(_viewWidth, 0);
        [self addSubview:_scrollView];
        
        //设置三个view的frame，加到scrollview上
        _leftView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, _viewWidth, _viewHeight)];
//        _leftView.contentMode = UIViewContentModeScaleAspectFit;
        [_scrollView addSubview:_leftView];
        
        _middleView = [[UIImageView alloc] initWithFrame:CGRectMake(_viewWidth, 0, _viewWidth, _viewHeight)];
//        _middleView.contentMode = UIViewContentModeScaleAspectFit;
        [_scrollView addSubview:_middleView];
        
        _rightView = [[UIImageView alloc] initWithFrame:CGRectMake(_viewWidth*2, 0, _viewWidth, _viewHeight)];
//        _rightView.contentMode = UIViewContentModeScaleAspectFit;
        [_scrollView addSubview:_rightView];
        
        //设置单击手势
        _tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(handleTap:)];
        _tap.numberOfTapsRequired = 1;
        _tap.numberOfTouchesRequired = 1;
        [_scrollView addGestureRecognizer:_tap];
    
    }
    return self;
}


#pragma mark 单击手势
-(void)handleTap:(UITapGestureRecognizer*)sender {
    if ([_delegate respondsToSelector:@selector(didClickPage:atIndex:)]) {
        [_delegate didClickPage:self atIndex:_currentImageIndex];
    }
}

#pragma mark 设置imageViewAry
-(void)setImageAry:(NSMutableArray *)imageAry {
    if (imageAry) {
        _imageAry = imageAry;
        _currentImageIndex = 0; //默认为第0页
        [self setInfoByCurrentImageIndex:_currentImageIndex];
    }
}

- (void)setInfoByCurrentImageIndex:(NSUInteger)currentImageIndex {
    _middleView.image = [_imageAry objectAtIndex:currentImageIndex];
    _leftView.image = [_imageAry objectAtIndex:(currentImageIndex - 1 + _imageAry.count)%_imageAry.count];
    _rightView.image = [_imageAry objectAtIndex:(currentImageIndex + 1)%_imageAry.count];

}

#pragma mark 刷新view页面
-(void)reloadData {
    CGPoint contentOffset = [_scrollView contentOffset];
    if (contentOffset.x > _viewWidth) { //向左滑动
        _currentImageIndex = (_currentImageIndex + 1) % _imageAry.count;
    } else if (contentOffset.x < _viewWidth) { //向右滑动
        _currentImageIndex = (_currentImageIndex - 1 + _imageAry.count)%_imageAry.count;
    }
    
    [self setInfoByCurrentImageIndex:_currentImageIndex];
    _scrollView.contentOffset = CGPointMake(_viewWidth, 0.0);
}

#pragma mark - UIScrollViewDelegate
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    if (self.imageAry.count == 1) {
        _scrollView.contentSize = CGSizeMake(_viewWidth, _viewHeight);
        return;
    }
    
    [self stopTimer];
    
    [self reloadData];
    
    [self startTimer];
}

#pragma mark 自动滚动
-(void)shouldAutoShow:(BOOL)shouldStart {
    if (self.imageAry.count == 1) {
        _scrollView.contentSize = CGSizeMake(_viewWidth, _viewHeight);
        return;
    }
    if (shouldStart) {  //开启自动翻页
        [self startTimer];
    }else {   //关闭自动翻页
        [self stopTimer];
    }
}

- (void)startTimer {
    if (!_autoScrollTimer) {
        _autoScrollTimer = [NSTimer scheduledTimerWithTimeInterval:1.5f target:self selector:@selector(autoShowNextImage) userInfo:nil repeats:YES];
    }
}

- (void)stopTimer {
    if (_autoScrollTimer.isValid) {
        [_autoScrollTimer invalidate];
        _autoScrollTimer = nil;
    }
}

#pragma mark 展示下一页
-(void)autoShowNextImage {
    [_scrollView scrollRectToVisible:CGRectMake(_viewWidth * 2, 0, _viewWidth, _viewHeight) animated:YES];
    [self reloadData];
}

- (void)dealloc {
    [_autoScrollTimer invalidate];
    _autoScrollTimer = nil;
    _scrollView.delegate = nil;
}

@end