UICollectionViewFlowLayout懶加載

- (UICollectionViewFlowLayout *)flowLayout {
    if (!_flowLayout) {
        _flowLayout = [[UICollectionViewFlowLayout alloc] init];
        //每個(gè)item大小
        _flowLayout.itemSize = CGSizeMake(165, 250);
        //間距
//        CGFloat spacing = (kScreenWidth - 300) / 4.0;
        //最小行間距
        _flowLayout.minimumLineSpacing = 15;
        //最小列間距
        _flowLayout.minimumInteritemSpacing = 30;
        //上下左右四個(gè)邊緣的間距
        //每個(gè)區(qū)的上下左右
        _flowLayout.sectionInset = UIEdgeInsetsMake(15, 15, 15, 15);
        
    }
    return _flowLayout;
}

UICollectionView懶加載

- (UICollectionView *)collectionView {
    if (!_collectionView) {
        _collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:self.flowLayout];
        _collectionView.backgroundColor = [UIColor clearColor];
        //代理
        _collectionView.dataSource = self;
        _collectionView.delegate = self;
    }
    return _collectionView;
}

注冊(cè)item

    //注冊(cè)item
    [self.collectionView registerClass:[customCell class] forCellWithReuseIdentifier:@"Cell"];

代理方法
簽訂協(xié)議<UICollectionViewDataSource, UICollectionViewDelegate>

//item個(gè)數(shù)
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return self.dataSource.count;
}
//分區(qū)數(shù)
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 2;
}
//item
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    customCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    cell.backgroundColor = [UIColor yellowColor];
    //獲取cell對(duì)應(yīng)的圖片
    NSDictionary *URLDic = self.dataSource[indexPath.item];
    //獲取字典內(nèi)的圖片網(wǎng)址
    NSString *imageURL = URLDic[@"thumbURL"];
    NSString *imageWidth = [NSString stringWithFormat:@"%@", URLDic[@"width"]];
    cell.widthLabel.text = imageWidth;
    //居中
    cell.widthLabel.textAlignment = NSTextAlignmentCenter;
    NSURL *imageurl = [NSURL URLWithString:imageURL];
    //獲取圖片
    [cell.imageView sd_setImageWithURL:imageurl placeholderImage:[UIImage imageNamed:@"placeholder"]];
    //圖片失真解決方法
    cell.imageView.contentMode = UIViewContentModeScaleAspectFit;
    return cell;
}
//item點(diǎn)擊方法
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
        NSLog(@"點(diǎn)擊");
}

注冊(cè)分區(qū)頭和分區(qū)尾

    //注冊(cè)分區(qū)頭
    [self.collectionView registerClass:[UICollectionViewCell class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"header"];
    //注冊(cè)分區(qū)尾
    [self.collectionView registerClass:[UICollectionViewCell class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"footer"];

分區(qū)頭分區(qū)尾代理方法

//分區(qū)尾大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section {
    return CGSizeMake(0, 30);
}
//分區(qū)頭大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section {
    return CGSizeMake(0, 30);
}
//分區(qū)頭部尾部協(xié)議方法
//分區(qū)頭部尾部共用一個(gè)協(xié)議方法
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        //獲取分區(qū)頭是從重用隊(duì)列去取的雹顺，而不是alloc init 的的
        UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"header" forIndexPath:indexPath];
        headerView.backgroundColor = [UIColor lightGrayColor];
        UILabel *headerLabel = [[UILabel  alloc] init];
        headerLabel.frame = CGRectMake(0, 0, 150, 30);
        headerLabel.text = @"header--美女";
        headerLabel.backgroundColor = [UIColor redColor];
        [headerView addSubview:headerLabel];
        
        return headerView;
    }else {
        UICollectionReusableView *footerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"footer" forIndexPath:indexPath];
        footerView.backgroundColor = [UIColor lightGrayColor];
        UILabel *footerLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 150, 30)];
        footerLabel.text = @"footer--漂亮";
        footerLabel.backgroundColor = [UIColor greenColor];
        [footerView addSubview:footerLabel];
        
        return footerView;
    }
    
}