dengwanli/SDK/UI/CarouselView/TXCarouselViewLayout.m

//
//  TXCarouselViewLayout.m
//  HJCarouselDemo
//
//  Created by 新华龙mac on 2018/1/17.
//  Copyright © 2018年 新华龙mac. All rights reserved.
//

#import "TXCarouselViewLayout.h"

#define INTERSPACEPARAM  0.90
@interface TXCarouselViewLayout ()
@property (nonatomic, assign) CGFloat collectionViewWidth;
@property (nonatomic, assign) CGFloat itemWidth;
@property (nonatomic, assign) CGFloat lastDirectionIndex;
@property (nonatomic, assign) CGFloat slidDistance;
@property (nonatomic, strong) NSIndexPath *lastIndexOne;
@end

@implementation TXCarouselViewLayout

/**
 * 当collectionView的显示范围发生改变的时候，是否需要重新刷新布局
 * 一旦重新刷新布局，就会重新调用下面的方法
 1.prepareLayout
 2.layoutAttributesForElementsInRect:方法
 */
- (void)prepareLayout{
    [super prepareLayout];
    self.visibleCount = 9;
    self.collectionViewWidth = CGRectGetWidth(self.collectionView.frame);
    self.itemWidth = self.itemSize.width;
//    self.itemWidth = self.itemSize.width;
}

- (CGSize)collectionViewContentSize{
    NSInteger cellCount = [self.collectionView numberOfItemsInSection:0];
    if (self.scrollDirection == UICollectionViewScrollDirectionVertical){
        return CGSizeMake(CGRectGetWidth(self.collectionView.frame), cellCount * self.itemWidth);
    }
    return CGSizeMake(cellCount * self.itemWidth, CGRectGetHeight(self.collectionView.frame));
}

/**
 * 这个方法的返回值是一个数组（数组里面存放着rect范围内所有元素的布局属性）
 * 这个数组中存放的都是UICollectionViewLayoutAttributes对象
 * 这个方法的返回值决定了rect范围内所有元素的排布（frame）
 * */
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
    
    NSInteger cellCount = [self.collectionView numberOfItemsInSection:0];
    CGFloat centerX =  self.collectionView.contentOffset.x + self.collectionViewWidth / 2;
    NSInteger totalCount = centerX / self.itemWidth;
    NSInteger count = (self.visibleCount) / 2;
    NSInteger minIndex = MAX(0, (totalCount - count));
    NSInteger maxIndex = MIN((cellCount - 1), (totalCount + count));
//    NSLog(@"minIndex = %ld  maxIndex = %ld",minIndex,maxIndex);
    NSMutableArray *array = [NSMutableArray array];
    for (NSInteger i = minIndex; i <= maxIndex; i++){
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
        UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];
        [array addObject:attributes];
    }
    return array;
    //
    
}

//返回每个cell的中心值和 缩放系数
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
    
    UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    attributes.size = self.itemSize;
    CGFloat cX = self.collectionView.contentOffset.x + self.collectionViewWidth / 2;
    CGFloat attributesX = self.itemWidth * indexPath.row + self.itemWidth / 2;//
    attributes.zIndex = -ABS(attributesX - cX);
    CGFloat delta = cX - attributesX;
    CGFloat ratio =  - delta / (self.itemWidth * 2);
    CGFloat scale = 0.6 - ABS(delta) / (self.itemWidth * 6.0) * cos(ratio * M_2_PI*0.9);
    attributes.transform = CGAffineTransformMakeScale(scale, scale);
    CGFloat centerY = attributesX;
//    NSLog(@"scale= %f",scale);
//    NSLog(@"indexPath = %ld",(long)indexPath.row);
//    NSLog(@"self.lastIndexOne = %ld",(long)self.lastIndexOne.row);
//    NSLog(@"scale ======== %f",scale);
    if (scale>0.999){//滑动到最前面时， 交换持有者
         self.lastIndexOne = indexPath;
    }
    if (self.lastIndexOne == indexPath){
        CGFloat index1 = 0.0f;
        if ([self judgeDirection:centerY]){
            index1 = 2;
        }else{
            index1 = -2;
        }
        centerY = cX + sin(ratio * 1.31) * self.itemWidth * INTERSPACEPARAM*2.2+index1;
        //双保险，如果滑动急快的情况下，方法没有获取到最高点的坐标会导致判断失败scale>0.999 实效，
        //所以启用判断scale <= 0.84加以纠正。(且只有在上述方法实效的情况下调用，所以不能使用|| ，不然有冲突，)
        if (scale <= 0.84){
            if ([self judgeDirection:centerY]){
                NSIndexPath *indexNext = [NSIndexPath indexPathForRow:self.lastIndexOne.row+1 inSection:0];
                self.lastIndexOne = indexNext;
            }else{
                NSIndexPath *indexNext = [NSIndexPath indexPathForRow:self.lastIndexOne.row-1 inSection:0];
                self.lastIndexOne = indexNext;
            }
        }
        if (scale <=0.9172) {
            CGFloat sinIndex = sin(ratio * 1.31) * self.itemWidth * INTERSPACEPARAM*2.7+index1;
            if ([self judgeDirection:centerY]) {
                centerY = centerY-(sinIndex+(self.itemSize.width*96/124));
            }else{
                centerY = centerY-(sinIndex-(self.itemSize.width*96/124));
            }
        }
        self.lastDirectionIndex = centerY;
    }else{
        centerY = cX + sin(ratio * 1.217) * self.itemWidth * INTERSPACEPARAM;
    }
    attributes.center = CGPointMake(centerY, CGRectGetHeight(self.collectionView.frame) / 2);
    return attributes;
    
}

/**
 * 这个方法的返回值，就决定了collectionView停止滚动时的偏移量
 * 这个方法在滚动松手的那一刻调用
 */
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity{
    
//    NSLog(@"proposedContentOffset = (%f,%f)",proposedContentOffset.x,proposedContentOffset.y);
//    NSLog(@"velocity = (%f,%f)",velocity.x,velocity.y);

    CGFloat index = roundf((proposedContentOffset.x + self.collectionViewWidth / 2 - self.itemWidth / 2) / self.itemWidth);
//    NSLog(@"test1 = %f",proposedContentOffset.x + self.collectionViewWidth / 2 - self.itemWidth / 2);
//    NSLog(@"test2 = %f",(proposedContentOffset.x + self.collectionViewWidth / 2 - self.itemWidth / 2) / self.itemWidth);
//    [index intVelue];
//    NSLog(@"self.collectionViewWidth = %f",self.collectionViewWidth);
//    NSLog(@"self.itemWidth = %f",self.itemWidth);
//    NSLog(@"indexindexindexindex = %f",index);
    proposedContentOffset.x = self.itemWidth * index + self.itemWidth / 2 - self.collectionViewWidth / 2;
    // proposedContentOffset 预计的位置（滚动结束时）
    
    NSInteger i = (NSInteger)index;
    [[NSNotificationCenter defaultCenter] postNotificationName:@"ThisIsANoticafication" object:@{@"parameter":@(i)}];
    
//    //leon 回调i值
//    NSInteger i = (NSInteger)index;
//    if (self.TargetScrollEnd){
//        self.TargetScrollEnd(i);
//    }
    
    return proposedContentOffset;
    
}

//判断滑动的方向(yes往左，no为右)；
-(BOOL)judgeDirection:(CGFloat)index{
    
    if (self.lastDirectionIndex>index){
        NSLog(@"滑动 = YES");
        return YES;
    }else{
        NSLog(@"滑动 = NO");
        return NO;
    }

}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
    return YES;
}

@end