iOS UICollectionView预加载

基类

//
//  WGBasePreloadCollectionView.m
//  weGood
//
//  Created by 黄龙山 on 2019/8/28.
//  Copyright © 2019 changdaokeji. All rights reserved.
//

#import "WGBasePreloadCollectionView.h"
#import "WGNetWorkUtil.h"

@implementation WGBasePreloadCollectionView
#pragma mark - refresh
- (void)hideFooter {
    self.mj_footer.hidden = YES;
}

- (void)showFooter {
    self.mj_footer.hidden = NO;
}

- (void)endRefreshNoMoreData {
    [self.mj_footer endRefreshing];
    self.mj_footer.state = MJRefreshStateNoMoreData;
}

- (void)endRefresh {
    [self.mj_header endRefreshing];
    [self.mj_footer endRefreshing];
}

- (void)beginRefresh {
    [self.mj_header beginRefreshing];
}

#pragma mark - 上拉加载更多
- (void)setLoadMoreData:(void (^)(void))loadMoreData {
    _loadMoreData = loadMoreData;
    __weak typeof(self)weakSelf = self;
    MJRefreshAutoNormalFooter *footer = [MJRefreshAutoNormalFooter footerWithRefreshingBlock:^{
        weakSelf.loadMoreData();
    }];
    self.mj_footer = footer;
}

#pragma mark - 下拉刷新
- (void)setLoadNewData:(void (^)(void))loadNewData {
    if (@available(iOS 11.0, *)) {
        self.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    }
    _loadNewData = loadNewData;
    __weak typeof(self)weakSelf = self;
    
    MJRefreshNormalHeader *header = [MJRefreshNormalHeader headerWithRefreshingBlock:^{
        weakSelf.isPreLoadRefreshing = NO;
        weakSelf.isPreLoadLastPage = NO;
        weakSelf.loadNewData();
    }];
    self.mj_header = header;
}
#pragma mark - 预加载功能的封装
- (void)preLoadDataThreshold4WithPageSize:(CGFloat)pageSize initialPage:(int)initialPage curPage:(NSUInteger)curPage preLoadFetchBlk:(void(^)(void))preLoadFetchBlk noNetWorkBlk:(void(^)(void))noNetWorkBlk{
    [self preLoadDataWithThreshold:(pageSize-4)/(pageSize*1.0) pageSize:pageSize initialPage:initialPage curPage:curPage preLoadFetchBlk:preLoadFetchBlk noNetWorkBlk:noNetWorkBlk];
}

- (void)preLoadDataWithThreshold:(CGFloat)threshold pageSize:(CGFloat)pageSize initialPage:(int)initialPage curPage:(NSUInteger)curPage preLoadFetchBlk:(void(^)(void))preLoadFetchBlk noNetWorkBlk:(void(^)(void))noNetWorkBlk{
    
    self.threshold = threshold;
    self.pageSize = pageSize;
    self.initialPage = initialPage;
    self.curPage = curPage;
    self.preLoadFetchBlk = preLoadFetchBlk;
    
    __weak typeof(self) weakSelf = self;
    self.preLoadFooter = [MJRefreshAutoNormalFooter footerWithRefreshingBlock:^{
        if (![WGNetWorkUtil isNetConnected]) {
            [weakSelf.mj_footer endRefreshing];
            if (noNetWorkBlk) {
                noNetWorkBlk();
            }
            NSLog(@"似乎已断开与互联网的连接!");
        }
    }];
    self.mj_footer = self.preLoadFooter;
    
    self.isHavePreLoad = YES;
    [self addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:nil];
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{
    
    CGPoint pointNew = [change[NSKeyValueChangeNewKey]CGPointValue];
    CGPoint pointOld = [change[NSKeyValueChangeOldKey]CGPointValue];
    
    
    if ([keyPath isEqualToString:@"contentOffset"] && (pointNew.y > pointOld.y)) {
        if (pointNew.y > 0) {
            [self preLoadMethodWithScrollView:self threshold:self.threshold pageSize:self.pageSize initialPage:self.initialPage curPage:self.curPage preLoadFetchBlk:self.preLoadFetchBlk];
        }
    }
}

- (void)preLoadMethodWithScrollView:(UIScrollView *)scrollView threshold:(CGFloat )threshold pageSize:(CGFloat)pageSize initialPage:(int) initialPage curPage:(NSUInteger)curPage preLoadFetchBlk:(void(^)(void))preLoadFetchBlk{
    
    CGFloat current = scrollView.contentOffset.y + scrollView.frame.size.height;
    CGFloat total = scrollView.contentSize.height;
    CGFloat ratio = current / total;
    
    int pageCur = 0;
    if (initialPage == 1) {
        pageCur = initialPage - 1;
    }
    
    CGFloat needRead = pageSize * threshold + pageCur * pageSize;
    CGFloat totalItem = pageSize * (pageCur + 1);
    CGFloat newThreshold = needRead / totalItem;
    
    __block BOOL isNoNetwork = NO;
    if (![WGNetWorkUtil isNetConnected]) {
        //没有网络
        isNoNetwork = YES;
    }
    
    if ((ratio >= newThreshold && isNoNetwork == NO) && (self.isPreLoadRefreshing == NO && self.isPreLoadLastPage == NO)) {
        self.isPreLoadRefreshing = YES;
        
        if (preLoadFetchBlk) {
            curPage += 1;
            preLoadFetchBlk();
        }
    }
}

- (void)dealloc{
    if (self.isHavePreLoad) {
        [self removeObserver:self forKeyPath:@"contentOffset"];
    }
}
@end

重写父类实现自定义

//
//  WGPreloadCollectionView.m
//  weGood
//
//  Created by 黄龙山 on 2019/8/28.
//  Copyright © 2019 changdaokeji. All rights reserved.
//

#import "WGPreloadCollectionView.h"

@implementation WGPreloadCollectionView

- (void)awakeFromNib{
    [super awakeFromNib];
}
- (instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if (self) {
    }
    return self;
}
#pragma mark - 重写父类实现自定义
//预加载功能样式
- (void)preLoadDataWithThreshold:(CGFloat)threshold pageSize:(CGFloat)pageSize initialPage:(int)initialPage curPage:(NSUInteger)curPage preLoadFetchBlk:(void(^)(void))preLoadFetchBlk noNetWorkBlk:(void(^)(void))noNetWorkBlk{
    
    [super preLoadDataWithThreshold:threshold pageSize:pageSize initialPage:initialPage curPage:curPage preLoadFetchBlk:preLoadFetchBlk noNetWorkBlk:noNetWorkBlk];
    [self.preLoadFooter setTitle:@"" forState:MJRefreshStateIdle];
    [self.preLoadFooter setTitle:@"" forState:MJRefreshStatePulling];
    [self.preLoadFooter setTitle:@"正在寻找你心水的宝贝" forState:MJRefreshStateRefreshing];
    [self.preLoadFooter setTitle:@"没有数据了" forState:MJAJRefreshStateNoMoreData];
}

- (void)preLoadDataThreshold4WithPageSize:(CGFloat)pageSize initialPage:(NSUInteger)initialPage curPage:(NSUInteger)curPage preLoadFetchBlk:(void (^)(void))preLoadFetchBlk{
    [super preLoadDataThreshold4WithPageSize:pageSize initialPage:initialPage curPage:curPage preLoadFetchBlk:preLoadFetchBlk noNetWorkBlk:^{
        [self makeToast:@"似乎已断开与互联网的连接!"];
    }];
    [self.preLoadFooter setTitle:@"没有数据了" forState:MJAJRefreshStateNoMoreData];
}

@end

网络请求函数需要加的设置

self.collectionView.isPreLoadLastPage=true;//是否最后一笔数据
self.collectionView.isPreLoadRefreshing = NO;//是否进行预加载中

调用

[self.collectionView preLoadDataThreshold4WithPageSize:20 initialPage:self.pageNum curPage:self.pageNum preLoadFetchBlk:^{
        weakSelf.pageNum++;
        [weakSelf getGoodsBrowsingData];
    }];

-----end.