封装了一个中间放大效果的iOS轮播视图

效果图

计算逻辑

设定在中间展示的size，即正常size，然后设置水平和竖直方向上的margin, 在view的origin和scrollView的contentoffset相等的时候，即
视图处在正中间的时候，最大，然后通过计算其他视图的origin和scrollView.contentoffset 的距离设置大小，和contentoffset这个位置的frame的距离为一个视图宽度的时候，达到最小size,即最大size减去margin。然后通过计算该视图的origin和 contentffset的差的绝对值，即距离 占 视图宽度的比例，计算需要缩小的size

核心代码

//
//  LBHorizontalLoopView.m
//  LBHorizontalLoopView
//
//  Created by liubo on 2021/8/29.
//#import "LBMiddleExpandLoopView.h"@interface LBMiddleExpandLoopView ()<UIScrollViewDelegate>@property (nonatomic, strong, readwrite) LBMiddleExpandLoopViewBaseCell *currentCell;@property (nonatomic, assign, readwrite) NSInteger currentSelectIndex;// 实际的个数
@property (nonatomic, assign) NSInteger realCount;// 显示的个数
@property (nonatomic, assign) NSInteger showCount;// 定时器
@property (nonatomic, weak) NSTimer     *timer;
@property (nonatomic, assign) NSInteger timerIndex;// 当前显示的cell大小
@property (nonatomic, assign) CGSize cellSize;@property (nonatomic, strong) NSMutableDictionary *viewClsDict;
@property (nonatomic, strong) NSMutableArray *visibleCells;
@property (nonatomic, strong) NSMutableArray *reusableCells;
@property (nonatomic, assign) NSRange        visibleRange;// 处理xib加载时导致的尺寸不准确问题
@property (nonatomic, assign) CGSize        originSize;@end@implementation LBMiddleExpandLoopView#pragma mark - Life Cycle
- (instancetype)initWithFrame:(CGRect)frame {if (self = [super initWithFrame:frame]) {[self initialization];}return self;
}- (instancetype)initWithCoder:(NSCoder *)aDecoder {if (self = [super initWithCoder:aDecoder]) {[self initialization];}return self;
}- (void)layoutSubviews {[super layoutSubviews];if (CGSizeEqualToSize(self.originSize, CGSizeZero)) return;// 解决xib加载时导致的布局错误问题if (!CGSizeEqualToSize(self.bounds.size, self.originSize)) {[self updateScrollViewAndCellSize];}
}// 解决当父视图释放时，当前视图因为NSTimer强引用而导致的不能释放
- (void)willMoveToSuperview:(UIView *)newSuperview {if (!newSuperview) {[self stopTimer];}
}- (void)dealloc {[self stopTimer];self.scrollView.delegate = nil;
}// 重新此方法是为了解决当cell超出UIScrollView时不能点击的问题
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {if ([self pointInside:point withEvent:event]) {// 判断点击的点是否在cell上for (UIView *cell in self.scrollView.subviews) {// 将cell的frame转换到当前视图上CGRect convertFrame = CGRectZero;convertFrame.size = cell.frame.size;convertFrame.origin.x = cell.frame.origin.x + self.scrollView.frame.origin.x - self.scrollView.contentOffset.x;convertFrame.origin.y = self.scrollView.frame.origin.y + cell.frame.origin.y;// 判断点击的点是否在cell上if (CGRectContainsPoint(convertFrame, point)) {// 修复cell上添加其他点击事件无效的bugUIView *view = [super hitTest:point withEvent:event];if (view == self || view == cell || view == self.scrollView) return cell;return view;}}// 判断点击的点是否在UIScrollView上CGPoint newPoint = CGPointZero;newPoint.x = point.x - self.scrollView.frame.origin.x + self.scrollView.contentOffset.x;newPoint.y = point.y - self.scrollView.frame.origin.y + self.scrollView.contentOffset.y;if ([self.scrollView pointInside:newPoint withEvent:event]) {return [self.scrollView hitTest:newPoint withEvent:event];}// 系统处理return [super hitTest:point withEvent:event];}return nil;
}#pragma mark - Public Methods
- (void)reloadData {// 移除所有cell[self.scrollView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];// 停止定时器[self stopTimer];// 加载数据if (self.dataSource && [self.dataSource respondsToSelector:@selector(numberOfCellsInCycleScrollView:)]) {// 实际个数self.realCount = [self.dataSource numberOfCellsInCycleScrollView:self];// 展示个数if (self.isInfiniteLoop) {self.showCount = self.realCount == 1 ? 1 : self.realCount * 3;}else {self.showCount = self.realCount;}}// 清除原始数据[self.visibleCells removeAllObjects];[self.reusableCells removeAllObjects];self.visibleRange = NSMakeRange(0, 0);//cell数量为1或defaultSelectIndex超过了当前数量if(self.defaultSelectIndex >= self.realCount) {self.defaultSelectIndex = 0;}if(self.realCount == 1) {self.timerIndex = 0;}for (NSInteger i = 0; i < self.showCount; i++){[self.visibleCells addObject:[NSNull null]];}__weak __typeof(self) weakSelf = self;[self refreshSizeCompletion:^{[weakSelf initialScrollViewAndCellSize];}];
}- (void)refreshSizeCompletion:(void(^)(void))completion {if (self.bounds.size.width == 0 || self.bounds.size.height == 0) {[self layoutIfNeeded];// 此处做延时处理是为了解决使用Masonry布局时导致的view的大小不能及时更新的bugdispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.0f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{if (self.bounds.size.width == 0 || self.bounds.size.height == 0) {[self refreshSizeCompletion:completion];}else {!completion ? : completion();}});}else {!completion ? : completion();}
}- (void)registerClass:(nonnull Class)cellClass forViewReuseIdentifier:(NSString *)identifier
{[self.viewClsDict setObject:NSStringFromClass(cellClass) forKey:identifier];
}- (__kindof LBMiddleExpandLoopViewBaseCell *)dequeueReusableCellWithIdentifier:(NSString *)identifier
{LBMiddleExpandLoopViewBaseCell *cell;for (LBMiddleExpandLoopViewBaseCell *cellReusable in self.reusableCells){if ([cellReusable.reuseIdentifier isEqualToString:identifier]) {cell = cellReusable;}}if (!cell) {Class cellCls = NSClassFromString(self.viewClsDict[identifier]);cell = [[cellCls alloc] initWithReuseIdentifier:identifier];cell.userInteractionEnabled = NO;} else {[self.reusableCells removeObject:cell];}return cell;
}- (void)scrollToCellAtIndex:(NSInteger)index animated:(BOOL)animated {if (index < self.realCount) {[self stopTimer];if (self.isInfiniteLoop) {self.timerIndex = self.realCount + index;[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(startTimer) object:nil];[self performSelector:@selector(startTimer) withObject:nil afterDelay:0.5];} else {self.timerIndex = index;}[self.scrollView setContentOffset:CGPointMake(self.cellSize.width * self.timerIndex, 0) animated:animated];[self setupCellsWithContentOffset:self.scrollView.contentOffset];[self updateVisibleCellAppearance];}
}- (void)adjustCurrentCell {if (self.isAutoScroll && self.realCount > 0) {self.scrollView.contentOffset = CGPointMake(self.cellSize.width * self.timerIndex, 0);}
}- (void)startTimer {if (self.realCount > 1 && self.isAutoScroll) {[self stopTimer];//        NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:self.autoScrollTime target:self selector:@selector(timerUpdate) userInfo:nil repeats:YES];
//        [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];//  self.timer = timer;}
}- (void)stopTimer {if (self.timer) {[self.timer invalidate];self.timer = nil;}
}#pragma mark Private Methods
- (void)initialization {// 初始化默认数据self.clipsToBounds      = YES;self.isAutoScroll       = YES;self.isInfiniteLoop     = YES;self.minimumCellAlpha   = 1.0f;self.autoScrollTime     = 3.0f;// 添加scrollView[self addSubview:self.scrollView];
}- (void)initialScrollViewAndCellSize {self.originSize = self.bounds.size;[self updateScrollViewAndCellSize];// 默认选中if (self.defaultSelectIndex >= 0 && self.defaultSelectIndex < self.realCount) {[self handleCellScrollWithIndex:self.defaultSelectIndex];}
}- (void)updateScrollViewAndCellSize {if (self.bounds.size.width <= 0 || self.bounds.size.height <= 0) return;// 设置cell尺寸self.cellSize = CGSizeMake(self.bounds.size.width - 2 * self.leftRightMargin, self.bounds.size.height);if (self.delegate && [self.delegate respondsToSelector:@selector(sizeForCellInCycleScrollView:)]) {self.cellSize = [self.delegate sizeForCellInCycleScrollView:self];}// 设置scrollView大小self.scrollView.frame = CGRectMake(0, 0, self.cellSize.width, self.cellSize.height);self.scrollView.contentSize = CGSizeMake(self.cellSize.width * self.showCount,0);self.scrollView.center = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));if (self.realCount > 1) {CGPoint offset = CGPointZero;if (self.isInfiniteLoop) { // 开启无限轮播// 滚动到第二组offset = CGPointMake(self.cellSize.width * (self.realCount + self.defaultSelectIndex), 0);self.timerIndex = self.realCount + self.defaultSelectIndex;}else {offset = CGPointMake(self.cellSize.width * self.defaultSelectIndex, 0);self.timerIndex = self.defaultSelectIndex;}[self.scrollView setContentOffset:offset animated:NO];// 自动轮播if (self.isAutoScroll) {[self startTimer];}}// 根据当前scrollView的offset设置显示的cell[self setupCellsWithContentOffset:self.scrollView.contentOffset];// 更新可见cell的显示[self updateVisibleCellAppearance];
}- (void)setupCellsWithContentOffset:(CGPoint)offset {if (self.showCount == 0) return;if (self.cellSize.width <= 0 || self.cellSize.height <= 0) return;//计算_visibleRangeCGFloat originX = self.scrollView.frame.origin.x == 0 ? 0.01 : self.scrollView.frame.origin.x;CGFloat originY = self.scrollView.frame.origin.y == 0 ? 0.01 : self.scrollView.frame.origin.y;CGPoint startPoint = CGPointMake(offset.x - originX, offset.y - originY);CGPoint endPoint = CGPointMake(offset.x + self.scrollView.frame.size.width + originX, offset.y + self.scrollView.frame.size.height + originY);NSInteger startIndex = 0;for (NSInteger i = 0; i < self.visibleCells.count; i++) {if (self.cellSize.width * (i + 1) > startPoint.x) {startIndex = i;break;}}NSInteger endIndex = startIndex;for (NSInteger i = self.visibleCells.count - 1; i >= startIndex; i --) {if (self.cellSize.width * i < endPoint.x) {endIndex = i;break;}}// 可见页分别向前向后扩展一个，提高效率startIndex = MAX(startIndex, 0);endIndex = MIN(endIndex, self.visibleCells.count - 1);self.visibleRange = NSMakeRange(startIndex, endIndex - startIndex + 1);for (NSInteger i = startIndex; i <= endIndex; i++) {[self addCellAtIndex:i];}for (NSInteger i = 0; i < startIndex; i ++) {[self removeCellAtIndex:i];}for (NSInteger i = endIndex + 1; i < self.visibleCells.count; i ++) {[self removeCellAtIndex:i];}
}- (void)updateVisibleCellAppearance {if (self.showCount == 0) return;if (self.cellSize.width <= 0 || self.cellSize.height <= 0) return;CGFloat offsetX = self.scrollView.contentOffset.x;for (NSInteger i = self.visibleRange.location; i < NSMaxRange(self.visibleRange); i++) {LBMiddleExpandLoopViewBaseCell *cell = self.visibleCells[i];CGFloat originX = cell.frame.origin.x;CGFloat delta = fabs(originX - offsetX);CGRect originCellFrame = (CGRect){{self.cellSize.width * i, 0}, self.cellSize};CGFloat leftRightInset = 0;CGFloat topBottomInset = 0;CGFloat alpha = 0;if (delta < self.cellSize.width) {alpha = (delta / self.cellSize.width) * self.minimumCellAlpha;CGFloat adjustLeftRightMargin = self.leftRightMargin == 0 ? 0 : self.leftRightMargin + 1;CGFloat adjustTopBottomMargin = self.topBottomMargin == 0 ? 0 : self.topBottomMargin;leftRightInset = adjustLeftRightMargin * delta / self.cellSize.width;topBottomInset = adjustTopBottomMargin * delta / self.cellSize.width;NSInteger index = self.realCount == 0 ? 0 : i % self.realCount;if (index == self.currentSelectIndex) {[self.scrollView bringSubviewToFront:cell];}} else {alpha = self.minimumCellAlpha;leftRightInset = self.leftRightMargin;topBottomInset = self.topBottomMargin;[self.scrollView sendSubviewToBack:cell];}if (self.leftRightMargin == 0 && self.topBottomMargin == 0) {cell.frame = originCellFrame;}else {CGFloat scaleX = (self.cellSize.width - leftRightInset * 2) / self.cellSize.width;CGFloat scaleY = (self.cellSize.height - topBottomInset * 2) / self.cellSize.height;UIEdgeInsets insets = UIEdgeInsetsMake(topBottomInset, leftRightInset - 0.1, topBottomInset, leftRightInset);cell.layer.transform = CATransform3DMakeScale(scaleX, scaleY, 1.0);cell.frame = UIEdgeInsetsInsetRect(originCellFrame, insets);}// 获取当前cellif (cell.tag == self.currentSelectIndex) {self.currentCell = cell;}}
}- (void)addCellAtIndex:(NSInteger)index {NSParameterAssert(index >= 0 && index < self.visibleCells.count);LBMiddleExpandLoopViewBaseCell *cell = self.visibleCells[index];if ((NSObject *)cell == [NSNull null]) {cell = [self.dataSource cycleScrollView:self cellForViewAtIndex:index % self.realCount];if (cell) {[self.visibleCells replaceObjectAtIndex:index withObject:cell];cell.tag = index % self.realCount;__weak __typeof(self) weakSelf = self;cell.didCellClick = ^(NSInteger index) {[weakSelf handleCellSelectWithIndex:index];};cell.frame = CGRectMake(self.cellSize.width * index, 0, self.cellSize.width, self.cellSize.height);if (!cell.superview) {[self.scrollView addSubview:cell];}}}
}- (void)removeCellAtIndex:(NSInteger)index{LBMiddleExpandLoopViewBaseCell *cell = [self.visibleCells objectAtIndex:index];if ((NSObject *)cell == [NSNull null]) return;[self.reusableCells addObject:cell];if (cell.superview) {[cell removeFromSuperview];}[self.visibleCells replaceObjectAtIndex:index withObject:[NSNull null]];
}- (void)handleCellSelectWithIndex:(NSInteger)index {if ([self.delegate respondsToSelector:@selector(cycleScrollView:didSelectCellAtIndex:)]) {[self.delegate cycleScrollView:self didSelectCellAtIndex:index];}
}- (void)handleCellScrollWithIndex:(NSInteger)index {self.currentSelectIndex = index;// 获取当前cellfor (NSInteger i = self.visibleRange.location; i < NSMaxRange(self.visibleRange); i++) {LBMiddleExpandLoopViewBaseCell *cell = self.visibleCells[i];if (cell.tag == index) {self.currentCell = cell;}}if ([self.delegate respondsToSelector:@selector(cycleScrollView:didScrollCellToIndex:)]) {[self.delegate cycleScrollView:self didScrollCellToIndex:index];}
}- (void)timerUpdate {self.timerIndex++;// bug fixed：解决反向滑动停止后，可能出现的自动滚动错乱问题if (self.timerIndex > self.realCount * 2) {self.timerIndex = self.realCount * 2;}if (!self.isInfiniteLoop) {if (self.timerIndex >= self.realCount) {self.timerIndex = 0;}}[self.scrollView setContentOffset:CGPointMake(self.cellSize.width * self.timerIndex, 0) animated:YES];
}#pragma mark UIScrollView Delegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{if (self.realCount == 0) return;if (self.cellSize.width <= 0 || self.cellSize.height <= 0) return;NSInteger index = 0;index = (NSInteger)round(self.scrollView.contentOffset.x / self.cellSize.width) % self.realCount;if (self.isInfiniteLoop) {if (self.realCount > 1) {CGFloat horIndex = scrollView.contentOffset.x / self.cellSize.width;if (horIndex >= 2 * self.realCount) {scrollView.contentOffset = CGPointMake(self.cellSize.width * self.realCount, 0);self.timerIndex = self.realCount;}if (horIndex <= (self.realCount - 1)) {scrollView.contentOffset = CGPointMake(self.cellSize.width * (2 * self.realCount - 1), 0);self.timerIndex = 2 * self.realCount - 1;}}}else {index = 0;}[self setupCellsWithContentOffset:scrollView.contentOffset];[self updateVisibleCellAppearance];if (index >= 0 && self.currentSelectIndex != index) {[self handleCellScrollWithIndex:index];}[self handleScrollViewDidScroll:scrollView];
}- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {[self stopTimer];if ([self.delegate respondsToSelector:@selector(cycleScrollView:willBeginDragging:)]) {[self.delegate cycleScrollView:self willBeginDragging:scrollView];}
}// 结束拖拽时调用，decelerate是否有减速
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {if (!decelerate) {[self startTimer];}if ([self.delegate respondsToSelector:@selector(cycleScrollView:didEndDragging:willDecelerate:)]) {[self.delegate cycleScrollView:self didEndDragging:scrollView willDecelerate:decelerate];}
}// 结束减速是调用
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {[self startTimer];if ([self.delegate respondsToSelector:@selector(cycleScrollView:didEndDecelerating:)]) {[self.delegate cycleScrollView:self didEndDecelerating:scrollView];}
}- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {if (self.realCount > 1 && self.isAutoScroll) {NSInteger index = round(targetContentOffset->x / self.cellSize.width);self.timerIndex = index;}
}- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {[self updateVisibleCellAppearance];if ([self.delegate respondsToSelector:@selector(cycleScrollView:didEndScrollingAnimation:)]) {[self.delegate cycleScrollView:self didEndScrollingAnimation:scrollView];}
}- (void)handleScrollViewDidScroll:(UIScrollView *)scrollView {if ([self.delegate respondsToSelector:@selector(cycleScrollView:didScroll:)]) {[self.delegate cycleScrollView:self didScroll:scrollView];}if ([self.delegate respondsToSelector:@selector(cycleScrollView:scrollingFromIndex:toIndex:ratio:)]) {BOOL isFirstRevirse = NO; // 是否在第一个位置反向滑动CGFloat ratio = 0;   // 滑动百分比CGFloat offsetX = scrollView.contentOffset.x;CGFloat maxW = self.realCount * scrollView.bounds.size.width;CGFloat changeOffsetX = self.isInfiniteLoop ? (offsetX - maxW) : offsetX;if (changeOffsetX < 0) {changeOffsetX = -changeOffsetX;isFirstRevirse = YES;}ratio = (changeOffsetX / scrollView.bounds.size.width);if (ratio > self.realCount || ratio < 0) return; // 越界，不作处理ratio = MAX(0, MIN(self.realCount, ratio));NSInteger baseIndex = floor(ratio);if (baseIndex + 1 > self.realCount) {// 右边越界了baseIndex = 0;}CGFloat remainderRatio = ratio - baseIndex;if (remainderRatio <= 0 || remainderRatio >= 1) return;NSInteger toIndex = 0;if (isFirstRevirse) {baseIndex = self.realCount - 1;toIndex = 0;remainderRatio = 1 - remainderRatio;}else if (baseIndex == self.realCount - 1) {toIndex = 0;}else {toIndex = baseIndex + 1;}[self.delegate cycleScrollView:self scrollingFromIndex:baseIndex toIndex:toIndex ratio:remainderRatio];}
}#pragma mark - 懒加载
- (UIScrollView *)scrollView {if (!_scrollView) {_scrollView = [[UIScrollView alloc] initWithFrame:self.bounds];_scrollView.scrollsToTop = NO;_scrollView.delegate = self;_scrollView.pagingEnabled = YES;_scrollView.clipsToBounds = NO;_scrollView.showsHorizontalScrollIndicator = NO;_scrollView.showsVerticalScrollIndicator = NO;}return _scrollView;
}- (NSMutableArray *)visibleCells {if (!_visibleCells) {_visibleCells = [NSMutableArray new];}return _visibleCells;
}- (NSMutableDictionary *)viewClsDict
{if (!_viewClsDict) {_viewClsDict = [NSMutableDictionary dictionary];}return _viewClsDict;
}- (NSMutableArray *)reusableCells {if (!_reusableCells) {_reusableCells = [NSMutableArray new];}return _reusableCells;
}@end