iOS如何使用UICollectionView如何实现列表头部拉伸效果

//
// CustomCollectionViewFlowLayout.m
// 
//
// Created by GongHui_YJ on 16/8/4.
// Copyright © 2016年 Yangjian. All rights reserved.
//

#import "CustomCollectionViewFlowLayout.h"

@implementation CustomCollectionViewFlowLayout

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

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {

  UICollectionView *collectionView = [self collectionView];
  UIEdgeInsets insets = [collectionView contentInset];
  CGPoint offset = [collectionView contentOffset];
  CGFloat minY = -insets.top;

  NSArray *attributes = [super layoutAttributesForElementsInRect:rect];

  if (offset.y < minY) {

    CGSize headerSize = [self headerReferenceSize];
    CGFloat deltaY = fabsf(offset.y - minY);

    for (UICollectionViewLayoutAttributes *attrs in attributes) {

      if ([attrs representedElementKind] == UICollectionElementKindSectionHeader) {

        CGRect headerRect = [attrs frame];
        headerRect.size.height = MAX(minY, headerSize.height + deltaY);
        headerRect.origin.y = headerRect.origin.y - deltaY;
        [attrs setFrame:headerRect];
        break;
      }
    }
  }

  return attributes;
}

@end

// 创建collectionView
  CustomCollectionViewFlowLayout *flowLayout=[[CustomCollectionViewFlowLayout alloc] init];
  [flowLayout setSectionInset:UIEdgeInsetsMake(0, 0, 10, 0)];
  [flowLayout setItemSize:CGSizeMake(kScreenWidth / collectionCellW, kScreenWidth / collectionCellW)];
  [flowLayout setHeaderReferenceSize:CGSizeMake(kScreenWidth, userInfoImageViewH)];
  [flowLayout setFooterReferenceSize:CGSizeMake(kScreenWidth, 83)];
  [flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
  [flowLayout setMinimumInteritemSpacing:0.0];
  [flowLayout setMinimumLineSpacing:0.0];

  self.homeCollectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, kScreenWidth, kScreenHeight - 44)collectionViewLayout:flowLayout];
  self.homeCollectionView.backgroundColor = kViewBackgroundColor;
  self.homeCollectionView.alwaysBounceVertical = YES;
  self.homeCollectionView.showsVerticalScrollIndicator = NO;
  //设置代理
  self.homeCollectionView.delegate = self;
  self.homeCollectionView.dataSource = self;
  [self.view addSubview:self.homeCollectionView];

  // 注册表头
  [self.homeCollectionView registerClass:[YJHeaderCollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:kCollectionHeaderView];

  // 注册表尾
  [self.homeCollectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:kCollectionFooterView];

//
// CustomCollectionViewFlowLayout.swift
// 
//
// Created by GongHui_YJ on 16/8/4.
// Copyright © 2016年YangJian. All rights reserved.
//

import UIKit

class CustomCollectionViewFlowLayout: UICollectionViewFlowLayout {

  override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
    return true
  }

  override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    let collectionView = self.collectionView
    let insets = collectionView?.contentInset
    let offset = collectionView?.contentOffset
    let minY = -((insets?.top)!)

    let attributesArray = super.layoutAttributesForElementsInRect(rect)
    if offset!.y < minY {
      let headerSize = self.headerReferenceSize
      let deltaY = CGFloat(fabsf(Float((offset?.y)! - CGFloat(minY))))

      for attrs:UICollectionViewLayoutAttributes in attributesArray! {

        if attrs.representedElementKind == UICollectionElementKindSectionHeader {
          var headerRect = attrs.frame
          headerRect.size.height = max(minY, headerSize.height + deltaY)
          headerRect.origin.y = headerRect.origin.y - deltaY
          attrs.frame = headerRect
          break
        }
      }
    }

    return attributesArray
  }

}

let customFlowLayout = CustomCollectionViewFlowLayout()
  customFlowLayout.headerReferenceSize = CGSizeMake(kScreenWidth, 203)
  customFlowLayout.footerReferenceSize = CGSizeMake(kScreenWidth, 83)
  customFlowLayout.minimumInteritemSpacing = 0
  customFlowLayout.minimumLineSpacing = 0
  customFlowLayout.itemSize = CGSizeMake(kScreenWidth / 3.000006, kScreenWidth / 3.00006)
  customFlowLayout.sectionInset = UIEdgeInsetsMake(0, 0, 10, 0)

  self.homeCollectionView.setCollectionViewLayout(customFlowLayout, animated: true)
  self.homeCollectionView.backgroundColor = kViewBackgroundColor
  self.homeCollectionView.alwaysBounceVertical = true
  let nib = UINib(nibName: "CommonCollectionViewCell", bundle: nil)
  self.homeCollectionView.registerNib(nib, forCellWithReuseIdentifier: cellId)

  // 注册表头表尾
  let headerNib = UINib(nibName: "HeaderCollectionReusableView", bundle: nil)
  self.homeCollectionView.registerNib(headerNib, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, withReuseIdentifier: collectionHeaderId)

  self.homeCollectionView.registerClass(UICollectionReusableView.classForCoder(), forSupplementaryViewOfKind: UICollectionElementKindSectionFooter, withReuseIdentifier: collectionFooterId)