UICollectionView简单使用用法

- (UICollectionView *)collectionView {
    if (!_collectionView) {
        UICollectionViewFlowLayout *layout = [UICollectionViewFlowLayout new];
        layout.scrollDirection = UICollectionViewScrollDirectionVertical;
        layout.minimumLineSpacing = 8;
        layout.minimumInteritemSpacing = 8;
        layout.sectionInset = UIEdgeInsetsMake(self.cellTopMargin, 15, 12, 24);//section set
        CGFloat itemCellWidth = (ScreenWidth-15-24-3*8)/4;
        layout.itemSize = CGSizeMake(itemCellWidth, 30);
        layout.headerReferenceSize = CGSizeMake(ScreenWidth, self.sectionHeaderHeight);
        
        _collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
        _collectionView.dataSource = self;
        _collectionView.delegate = self;
        _collectionView.scrollsToTop = NO;
        _collectionView.showsVerticalScrollIndicator = NO;
        _collectionView.showsHorizontalScrollIndicator = NO;
        [_collectionView registerClass:[FHMatchFilterHeader class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:kCollectionHeaderIdentifier];
        
        [_collectionView registerClass:[FHMatchFilterCell class] forCellWithReuseIdentifier:kCollectionCellIdentifier];
        _collectionView.backgroundColor = [UIColor clearColor];
    }
    return _collectionView;
}

#pragma mark - UICollectionViewDelegate & UICollectionViewDataSource
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return self.cityList.count;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    NSDictionary *cityDict = [self.cityList objectAtIndex:section];
    NSArray *cityGroup = [cityDict valueForKey:[self.indexData objectAtIndex:section]];
    return cityGroup.count;
}

//下面注释的内容被上面的layout属性替换，就可以省略不写
//- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
//{
//    return UIEdgeInsetsMake(self.cellTopMargin, 15, 12, 24);
//}
//- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
//{
//    return 8;
//}
//
//- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
//{
//    return 8;
//}
//- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
//{
//    float itemCellWidth = (ScreenWidth-15-24-3*8)/4;
//    return CGSizeMake(itemCellWidth, 30);
//
//}

//cell
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    FHMatchFilterCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:kCollectionCellIdentifier forIndexPath:indexPath];
    NSDictionary *cityDict = [self.cityList objectAtIndex:indexPath.section];
    NSArray *cityGroup = [cityDict valueForKey:[self.indexData objectAtIndex:indexPath.section]];
    [cell updateCityName:[cityGroup objectAtIndex:indexPath.row]];
    return cell;
}

//section 头部高度
//- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section {
//    return CGSizeMake(ScreenWidth, self.sectionHeaderHeight);
//}

//section 头部view
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        FHMatchFilterHeader *header = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:kCollectionHeaderIdentifier forIndexPath:indexPath];
        NSString *title = self.indexData[indexPath.section];
        [header updateCityIndex:title];
        return header;
    }
    return nil;
}