erpsuiteios/common/InfinitePhoto/Controller/RAPhotoPreviewController.m

//
//  NewPhotoPreviewController.m
//  RA Image
//
//  Created by Jack on 2017/6/14.
//  Copyright © 2017年 USAI. All rights reserved.
//

#import "RAPhotoPreviewController.h"
#import "PhotoPreviewCell.h"

@interface RAPhotoItemPlaceHolder : NSObject <RAPhotoItemDelegate>

@property (nonatomic,weak) id<RAPhotoItemDelegate> model;
@property (nonatomic,weak) id<RAPhotoItemUIDelegate> delegate;
@property (nonatomic,strong) UIImage *image;

@end

@implementation RAPhotoItemPlaceHolder

- (instancetype)initWithModel:(id<RAPhotoItemDelegate>)model {
    if (self = [super init]) {
        self.model = model;
    }
    return self;
}

- (UIImage *)image {
    return self.model.image;
}

@end

#pragma mark - VC

@interface RAPhotoPreviewController ()<UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>

@property (nonatomic,assign) NSUInteger currentIndex;
@property (strong, nonatomic) IBOutlet UILabel *indicator;
@property (strong, nonatomic) IBOutlet UICollectionView *previewContainer;


@property (nonatomic,strong) NSArray<id<RAPhotoItemDelegate>> *photos;
@property (nonatomic,assign) NSUInteger offset;

@property (nonatomic,assign) BOOL hideNavigationBar;
@property (nonatomic,assign) BOOL initialized;

@end

@implementation RAPhotoPreviewController

+ (instancetype)ra_photoPreviewControllerWithPhotoItems:(NSArray<id<RAPhotoItemDelegate>> *)items offset:(NSUInteger)offset {
    
    RAPhotoPreviewController *vc = [[UIStoryboard storyboardWithName:@"PhotoList" bundle:nil] instantiateViewControllerWithIdentifier:@"RAPhotoPreviewController"];
    
    //  只有一张图片时，滑动会将View 和 Model 解绑，并且刷新View，导致看到黑色。
    if (items.count == 1) {
        NSMutableArray<id<RAPhotoItemDelegate>> *tmpArr = [NSMutableArray arrayWithArray:items];
        id<RAPhotoItemDelegate> item = items[0];
        RAPhotoItemPlaceHolder *placeHolder = [[RAPhotoItemPlaceHolder alloc] initWithModel:item];
        [tmpArr addObject:placeHolder];
        
        items = tmpArr;
    }
    
    if (offset == 0 || offset >= items.count) {
        vc.photos = items;
    } else {
        NSMutableArray<id<RAPhotoItemDelegate>> *tmpArr = [NSMutableArray array];
        [tmpArr addObjectsFromArray:[items subarrayWithRange:NSMakeRange(offset, items.count - offset)]];
        for (int i = 0; i < offset; i++) {
            id<RAPhotoItemDelegate> model = [items objectAtIndex:i];
            [tmpArr addObject:model];
        }
        items = [tmpArr copy];
        vc.photos = items;
    }
    vc.offset = offset;
    vc.currentIndex = 0;
    
    return vc;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    if (@available(iOS 11, *)) {
        self.previewContainer.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    } else {
        self.automaticallyAdjustsScrollViewInsets = NO;
    }
    
    self.indicator.layer.cornerRadius = 20;
    self.indicator.layer.masksToBounds = YES;
    self.previewContainer.pagingEnabled = YES;
    self.hideNavigationBar = self.navigationController.isNavigationBarHidden;
    self.navigationController.navigationBarHidden = YES;
    
    [self updateIndicator];
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

   [self.previewContainer setContentOffset:CGPointMake((self.currentIndex + 1) * CGRectGetWidth(self.previewContainer.frame), 0) animated:YES];
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    
    // 隐藏初始化时滚动效果
    self.initialized = YES;
    [self.previewContainer reloadItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:self.currentIndex + 1 inSection:0]]];

}

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
    [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];

    [coordinator animateAlongsideTransitionInView:self.previewContainer animation:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {

        // 重新布局 Item 大小
        [self.previewContainer.collectionViewLayout invalidateLayout];
        
    } completion:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
        
        [self.previewContainer reloadData];
    }];
}

- (BOOL)prefersStatusBarHidden {
    return YES;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - FlowLayout Delegate

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    return collectionView.bounds.size;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 0;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    return 0;
}

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    return UIEdgeInsetsZero;
}

#pragma mark - CollectionView Delegate

- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath {

    if (self.initialized) {
        
        NSUInteger idx = [self contentOffsetForIndexPath:indexPath];
        PhotoPreviewCell *preCell = (PhotoPreviewCell *)cell;
        id<RAPhotoItemDelegate> model = [self.photos objectAtIndex:idx];
        preCell.model = model;
    }
}

- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath {
    
    PhotoPreviewCell *preCell = (PhotoPreviewCell *)cell;
    [preCell reset];
}

#pragma mark - CollectionView DataSource

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    if ([self.photos count] == 0) {
        return 0;
    }
    return self.photos.count + 2;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    
    PhotoPreviewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"PhotoPreviewCell" forIndexPath:indexPath];
    cell.scrollView.delegate = self;
    return cell;
}

#pragma mark - ScrollView Delegate

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    if (scrollView == self.previewContainer) {
        
        CGFloat offsetX = scrollView.contentOffset.x;
        float idxf = offsetX / CGRectGetWidth(scrollView.frame);
        int idxi = (int)(offsetX / CGRectGetWidth(scrollView.frame));
        
        if (idxf == idxi) {
            if (idxi == 0) {
                self.currentIndex = self.photos.count - 1;
            } else if (idxi == self.photos.count + 1) {
                self.currentIndex = 0;
            } else {
                self.currentIndex = idxi - 1;
            }
            
            [self updateIndicator];
        } else {
            
        }
        
        if (idxi == 0) {
            [self scrollToIndex:self.photos.count];
        }
        
        if (idxi == self.photos.count + 1) {
            [self scrollToIndex:1];
        }
        
    }
    
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    if (scrollView != self.previewContainer) {
        return scrollView.subviews.firstObject;
    }
    return nil;
}

#pragma mark - Private

- (void)updateIndicator {

    /**
     
            x

    0 1 2 3 4 5 6 7 8 9

    4 5 6 7 8 9 0 1 2 3
     
     */
    NSUInteger index = (self.currentIndex + self.offset) % self.photos.count + 1;
    NSString *offset = [NSString stringWithFormat:@"%lu / %lu",index,(unsigned long)self.photos.count];
    self.indicator.text = offset;
}

- (NSUInteger)contentOffsetForIndexPath:(NSIndexPath *)indexPath {
    NSUInteger idx = indexPath.row;
    if (idx == 0) {
        idx = self.photos.count - 1;
    }else if (idx == self.photos.count + 1) {
        idx = 0;
    } else {
        idx = idx - 1;
    }
    return idx;
}

- (void)scrollToIndex:(NSUInteger)index { // 不会出现肉眼可见的滚动效果
    self.previewContainer.contentOffset = CGPointMake(index * CGRectGetWidth(self.previewContainer.frame), 0);
}

- (IBAction)closeBtnClick:(UIButton *)sender {
    
    if (self.navigationController) {
        self.navigationController.navigationBarHidden = self.hideNavigationBar;
        [self.navigationController popViewControllerAnimated:YES];
    } else {
        [self dismissViewControllerAnimated:YES completion:nil];
    }
    
}


@end