iOS利用余弦函数实现卡片浏览工具

//
// CardSwitchView.m
// CardSwitchDemo
//
// Created by Apple on 2016/11/9.
// Copyright © 2016年 Apple. All rights reserved.
//
 
#import "CardSwitchView.h"
#import "Card.h"
 
//播放器界面的的宽度所占的比例
static float viewScale = 0.70f;
 
@interface CardSwitchView ()<UIScrollViewDelegate>
{
 //用于切换的ScrollView
 UIScrollView *_scrollView;
 //用于保存各个视图
 NSMutableArray *_cards;
 //滚动之前的位置
 CGFloat _startPointX;
 //滚动之后的位置
 CGFloat _endPointX;
 //需要居中显示的index
 NSInteger _currentIndex;
}
@end
 
@implementation CardSwitchView
 
-(instancetype)initWithFrame:(CGRect)frame
{
 if (self = [super initWithFrame:frame]) {
 [self buildLayout];
 }
 return self;
}
 
 
-(void)buildLayout
{
 //初始化ScrollView
 _scrollView = [[UIScrollView alloc] initWithFrame:self.bounds];
 _scrollView.delegate = self;
 _scrollView.showsHorizontalScrollIndicator = false;
 [self addSubview:_scrollView];
 
 //初始化其他参数
 _cards = [[NSMutableArray alloc] init];
 _currentIndex = 0;
}
 
#pragma mark -
#pragma mark 视图Frame配置
 
//卡片宽度
-(float)cardWidth
{
 return viewScale*self.bounds.size.width;
}
 
//卡片间隔
-(float)margin
{
 return (self.bounds.size.width - [self cardWidth])/4;
}
//卡片起始位置
-(float)startX
{
 return (self.bounds.size.width - [self cardWidth])/2.0f;
}
 
#pragma mark -
#pragma mark 配置轮播图片
-(void)setCardNumber:(NSInteger)cardNumber
{
 _cardNumber = cardNumber;
 //初始化各个播放器位置
 for (NSInteger i = 0; i<cardNumber; i++ ) {
 //第一步 在ScrollView上添加卡片
 float viewX = [self startX] + i*([self cardWidth] + [self margin]);
 Card* card = [[Card alloc] initWithFrame:CGRectMake(viewX, 0, [self cardWidth], self.bounds.size.height)];
 card.layer.borderWidth = 1.0f;
 card.index = i;
 [_scrollView addSubview:card];
 [_cards addObject:card];
 [_scrollView setContentSize:CGSizeMake(card.frame.origin.x + [self cardWidth] + 2*[self margin], 0)];
 }
 //更新卡片的大小
 [self updateCardTransform];
}
 
#pragma mark -
#pragma mark ScrollView代理方法
//开始拖动时保存起始位置
-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
 _startPointX = scrollView.contentOffset.x;
}
 
//当ScrollView拖动时 变换每个view的大小，并保证居中屏幕的view高度最高
-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
 [self updateCardTransform];
}
 
//滚动结束，自动回弹到居中卡片
-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
 //滚动到视图中间位置
 dispatch_async(dispatch_get_main_queue(), ^{
 [self scrollToCurrentCard];
 });
}
 
//卡片自动居中
-(void)scrollToCurrentCard
{
 _endPointX = _scrollView.contentOffset.x;
 //设置滚动最小生效范围，滚动超过scrollMiniDistance 即视为有切换卡片的意向
 float scrollMiniDistance = self.bounds.size.width/30.0f;
 if (_startPointX - _endPointX > scrollMiniDistance) {
 NSLog(@"向右滑动屏幕");
 if (_currentIndex != 0) {
  _currentIndex -= 1;
 }
 }else if (_endPointX - _startPointX > scrollMiniDistance)
 {
 NSLog(@"向左滑动屏幕");
 if (_currentIndex != _cards.count - 1) {
  _currentIndex += 1;
 }
 }
 float viewX = [self startX] + _currentIndex*([self cardWidth] + [self margin]);
 float needX = viewX - [self startX];
 [_scrollView setContentOffset:CGPointMake(needX, 0) animated:true];
}
 
 
//更新每个卡片的大小
-(void)updateCardTransform
{
 for (Card *card in _cards) {
 //获取卡片所在index
 //获取ScrollView滚动的位置
 CGFloat scrollOffset = _scrollView.contentOffset.x;
 //获取卡片中间位置滚动的相对位置
 CGFloat cardCenterX = card.center.x - scrollOffset;
 //获取卡片中间位置和父视图中间位置的间距，目标是间距越大卡片越短
 CGFloat apartLength = fabs(self.bounds.size.width/2.0f - cardCenterX);
 //移动的距离和屏幕宽度的的比例
 CGFloat apartScale = apartLength/self.bounds.size.width;
 //把卡片移动范围固定到 -π/4到 +π/4这一个范围内
 CGFloat scale = fabs(cos(apartScale * M_PI/4));
 //设置卡片的缩放
 card.transform = CGAffineTransformMakeScale(1.0, scale);
 }
}
 
@end