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iOS-UICollectionView

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本章通过先总体介绍UICollectionView及其常用方法，再结合一个实例，了解如何使用UICollectionView。

UICollectionView 和 UICollectionViewController 类是iOS6 新引进的API，用于展示集合视图，布局更加灵活，可实现多列布局，用法类似于UITableView 和 UITableViewController 类。

使用UICollectionView 必须实现UICollectionViewDataSource,UICollectionViewDelegate,UICollectionViewDelegateFlowLayout这三个协议。

下面先给出常用到的一些方法。（只给出常用的，其他的可以查看相关API）

#pragma mark -- UICollectionViewDataSource

//定义展示的UICollectionViewCell的个数
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
return 30;
}

//定义展示的Section的个数
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return 1;
}

//每个UICollectionView展示的内容
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString * CellIdentifier = @"GradientCell";
UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
cell.backgroundColor = [UIColor colorWithRed:((10 * indexPath.row) / 255.0) green:((20 * indexPath.row)/255.0) blue:((30 * indexPath.row)/255.0) alpha:1.0f];
return cell;
}

#pragma mark --UICollectionViewDelegateFlowLayout

//定义每个UICollectionView 的大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
return CGSizeMake(96, 100);
}

//定义每个UICollectionView 的 margin
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
return UIEdgeInsetsMake(5, 5, 5, 5);
}

#pragma mark --UICollectionViewDelegate

//UICollectionView被选中时调用的方法
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell * cell = (UICollectionViewCell *)[collectionView cellForItemAtIndexPath:indexPath];
cell.backgroundColor = [UIColor whiteColor];
}

//返回这个UICollectionView是否可以被选择
-(BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
return YES;
}

下面通过一个例子具体介绍下。（例子来自网络。但是是通过第三方获得的，无法取得链接。还望见谅。）

iOS CollectionView的出现是一大福利，再也不用用TableView来定义复杂的多栏表格了，用法与Table类似，只是Cell必须自己添加，无默认模式

由于CollectionView没有默认的Cell布局，所以一般还是自定义方便又快捷

一、自定义Cell

1、新建类CollectionCell继承自UICollectionViewCell

2、新建Xib，命名为CollectionCell.xib

a.选中CollectionCell.xib删掉默认的View，从控件中拖一个Collection View Cell（图3）到画布中，设置大小为95*116；

b.选中刚刚添加的Cell，更改类名为CollectionCell，如图4

c.在CollectionCell.xib的CollectionCell中添加一个ImageView和一个Label（图5）

d.创建映射, 图6，图7

e.选中CollectionCell.m , 重写init方法

- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
// 初始化时加载collectionCell.xib文件
NSArray *arrayOfViews = [[NSBundle mainBundle] loadNibNamed:@"CollectionCell" owner:self options:nil];
// 如果路径不存在，return nil
if (arrayOfViews.count < 1)
{
return nil;
}
// 如果xib中view不属于UICollectionViewCell类，return nil
if (![[arrayOfViews objectAtIndex:0] isKindOfClass:[UICollectionViewCell class]])
{
return nil;
}
// 加载nib
self = [arrayOfViews objectAtIndex:0];
}
return self;
}

f.选中CollectionCell.xib 修改其identifier为CollectionCell。

二、定义UICollectionView；

1、拖动一个Collection View到指定ViewController的View上

2、连线dataSource和delegate，并创建映射，命名为CollectionView

3、选中CollectionView的标尺，将Cell Size的Width和Height改成与自定义的Cell一样的95*116,图8

4、选中CollectionView的属性,可以修改其属性，比如是垂直滑动，还是水平滑动，选择Vertical或Horizontal

5、选中CollectionViewCell，修改Class，继承自CollectionCell

5、在ViewDidLoad方法中声明Cell的类，在ViewDidLoad方法中添加，此句不声明，将无法加载，程序崩溃

其中,CollectionCell是这个Cell的标识（之前几步已经定义过了。）

[self.collectionView registerClass:[CollectionCell class] forCellWithReuseIdentifier:@"CollectionCell"];

6、在ViewController.h中声明代理

@interface ViewController : UIViewController<UICollectionViewDataSource,UICollectionViewDelegate>

7、在.m文件中实现代理方法

//每个section的item个数
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
return 12;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CollectionCell *cell = (CollectionCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"CollectionCell" forIndexPath:indexPath];
//图片名称
NSString *imageToLoad = [NSString stringWithFormat:@"%d.png", indexPath.row];
//加载图片
cell.imageView.image = [UIImage imageNamed:imageToLoad];
//设置label文字
cell.label.text = [NSString stringWithFormat:@"{%ld,%ld}",(long)indexPath.row,(long)indexPath.section];
return cell;
}

8 。效果如图10

点击某项后跳转事件与UITableView类似，实现代理方法

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath  

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UICollectionView基础

初始化部分：

UICollectionViewFlowLayout *flowLayout= [[UICollectionViewFlowLayout alloc]init];
self.myCollectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(20, 20, 250, 350) collectionViewLayout:flowLayout];
self.myCollectionView.backgroundColor = [UIColor grayColor];
[self.myCollectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@“myCell"];
self.myCollectionView.delegate = self;
self.myCollectionView.dataSource = self;

[self.view addSubview:self.myCollectionView];

UICollectionViewLayout

UICollectionViewLayout决定了UICollectionView如何显示在界面上，Apple提供了一个最简单的默认layout对象：UICollectionViewFlowLayout。

Flow Layout是一个Cells的线性布局方案，并具有页面和页脚。其可定制的内容如下：

itemSize属性

设定全局的Cell尺寸，如果想要单独定义某个Cell的尺寸，可以使用下面方法：

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath

minimumLineSpacing属性

设定全局的行间距，如果想要设定指定区内Cell的最小行距，可以使用下面方法：

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section

minimumInteritemSpacing属性

设定全局的Cell间距，如果想要设定指定区内Cell的最小间距，可以使用下面方法：

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section;

scrollDirection属性

设定滚动方向，有UICollectionViewScrollDirectionVertical和UICollectionViewScrollDirectionHorizontal两个值。

headerReferenceSize属性与footerReferenceSize属性

设定页眉和页脚的全局尺寸，需要注意的是，根据滚动方向不同，header和footer的width和height中只有一个会起作用。如果要单独设置指定区内的页面和页脚尺寸，可以使用下面方法：

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section

sectionInset属性

设定全局的区内边距，如果想要设定指定区的内边距，可以使用下面方法：

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;

然后需要实现三种类型的委托：UICollectionViewDataSource, UICollectionViewDelagate和UICollectionViewDelegateFlowLayout。

@interface ViewController : UIViewController <UICollectionViewDelegateFlowLayout, UICollectionViewDataSource>

因为UICollectionViewDelegateFlowLayout实际上是UICollectionViewDelegate的一个子协议，它继承了UICollectionViewDelegate，所以只需要在声明处写上UICollectionViewDelegateFlowLayout就行了。

UICollectionViewDataSource

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView

返回collection view里区(section)的个数，如果没有实现该方法，将默认返回1：

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 2;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section

返回指定区(section)包含的数据源条目数(number of items)，该方法必须实现：

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 7;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

返回某个indexPath对应的cell，该方法必须实现：

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"myCell" forIndexPath:indexPath];
    if(indexPath.section==0)
    {
        cell.backgroundColor = [UIColor redColor];
    }
    else if(indexPath.section==1)
    {
        cell.backgroundColor = [UIColor greenColor];
    }
    return cell;
}

UICollectionViewCell结构上相对比较简单，由下至上：

首先是cell本身作为容器view
然后是一个大小自动适应整个cell的backgroundView，用作cell平时的背景
再其次是selectedBackgroundView，是cell被选中时的背景
最后是一个contentView，自定义内容应被加在这个view上

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString*)kind atIndexPath:(NSIndexPath *)indexPath

为collection view添加一个补充视图(页眉或页脚)

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section

设定页眉的尺寸

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section

设定页脚的尺寸

- (void)registerClass:(Class)viewClass forSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString*)identifier

添加页眉和页脚以前需要注册类和标识：

添加补充视图的代码示例：

[self.myCollectionView registerClass:[MyHeadView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"hxwHeader"];
[self.myCollectionView registerClass:[MyHeadView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"hxwHeader"];

-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{
    CGSize size = {240,25};
    return size;
}

-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section
{
    CGSize size = {240,25};
    return size;
}

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    MyHeadView *headView;
    
    if([kind isEqual:UICollectionElementKindSectionHeader])
    {
         headView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"hxwHeader" forIndexPath:indexPath];
        [headView setLabelText:[NSString stringWithFormat:@"section %d's header",indexPath.section]];
    }
    else if([kind isEqual:UICollectionElementKindSectionFooter])
    {
        headView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"hxwHeader" forIndexPath:indexPath];
        [headView setLabelText:[NSString stringWithFormat:@"section %d's footer",indexPath.section]];
    }
    return headView;
}

MyHeadView.h

#import <UIKit/UIKit.h>

@interface MyHeadView : UICollectionReusableView
- (void) setLabelText:(NSString *)text;
@end

MyHeadView.m

#import "MyHeadView.h"

@interface MyHeadView()

@property (strong, nonatomic) UILabel *label;

@end

@implementation MyHeadView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
        self.label = [[UILabel alloc] init];
        self.label.font = [UIFont systemFontOfSize:18];
        [self addSubview:self.label];
    }
    return self;
}

- (void) setLabelText:(NSString *)text
{
    self.label.text = text;
    [self.label sizeToFit];
}

@end

在注册Cell和补充视图时，也可以用新建xib文件的方式：

[self.myCollectionView registerNib:[UINib nibWithNibName:@"MyCollectionCell" bundle:nil] forCellWithReuseIdentifier:@"hxwCell"];

[self.myCollectionView registerNib:[UINib nibWithNibName:@"MySupplementaryView" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"hxwHeader"];
    
[self.myCollectionView registerNib:[UINib nibWithNibName:@"MySupplementaryView" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"hxwFooter"];

用这种方式注册后，甚至可以不用新建类去绑定这个xib，直接通过viewWithTag的方式获取xib里的控件：

UICollectionReusableView *view =  [collectionView dequeueReusableSupplementaryViewOfKind :kind withReuseIdentifier:@"hxwHeader" forIndexPath:indexPath];

UILabel *label = (UILabel *)[view viewWithTag:1];

label.text = @"empty";

UICollectionViewDelegateFlowLayout

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath

设定指定Cell的尺寸

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    if(indexPath.section==0 && indexPath.row==1)
    {
        return CGSizeMake(50, 50);
    }
    else
    {
        return CGSizeMake(75, 30);
    }
}

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;

设定collectionView(指定区)的边距

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    if(section==0)
    {
        return UIEdgeInsetsMake(35, 25, 15, 25);
    }
    else
    {
        return UIEdgeInsetsMake(15, 15, 15, 15);
    }
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section

设定指定区内Cell的最小行距，也可以直接设置UICollectionViewFlowLayout的minimumLineSpacing属性

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    if(section==0)
    {
        return 10.0;
    }
    else
    {
        return 20.0;
    }
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section;

设定指定区内Cell的最小间距，也可以直接设置UICollectionViewFlowLayout的minimumInteritemSpacing属性

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    if(section==0)
    {
        return 10.0;
    }
    else
    {
        return 20.0;
    }
}

UICollectionViewDelegate

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath

当指定indexPath处的item被选择时触发

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
[self.myArray removeObjectAtIndex:indexPath.row];

[collectionView deleteItemsAtIndexPaths:[NSArray arrayWithObject:indexPath]];
}

P.s. 当你删除或添加元素时，一定要更新numberOfItemsInSection的返回情况。

- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath

当指定indexPath处的item被取消选择时触发，仅在允许多选时被调用

下面是三个和高亮有关的方法：

- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath

- (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath

- (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath

事件的处理顺序如下：

手指按下
shouldHighlightItemAtIndexPath (如果返回YES则向下执行，否则执行到这里为止)
didHighlightItemAtIndexPath (高亮)
手指松开
didUnhighlightItemAtIndexPath (取消高亮)
shouldSelectItemAtIndexPath (如果返回YES则向下执行，否则执行到这里为止)
didSelectItemAtIndexPath (执行选择事件)

如果只是简单实现点击后cell改变显示状态，只需要在cellForItemAtIndexPath方法里返回cell时，指定cell的selectedBackgroundView：

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"myCell" forIndexPath:indexPath];
    
    UIView* selectedBGView = [[UIView alloc] initWithFrame:cell.bounds];
    selectedBGView.backgroundColor = [UIColor blueColor];
    cell.selectedBackgroundView = selectedBGView;
    
    return cell;
}

如果要实现点击时(手指未松开)的显示状态与点击后(手指松开)的显示状态，则需要通过上面提到的方法来实现：

- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath
{
    return YES;
}

- (void)collectionView:(UICollectionView *)colView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell* cell = [colView cellForItemAtIndexPath:indexPath];
    
    [cell setBackgroundColor:[UIColor purpleColor]];
}

- (void)collectionView:(UICollectionView *)colView  didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell* cell = [colView cellForItemAtIndexPath:indexPath];
    
    [cell setBackgroundColor:[UIColor yellowColor]];
}
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3

iOS UICollectionView的实现

ios的UICollectionView并不能在iOS6之前的版本中使用，为了兼容之前的版本需要自定义UICollectionView。写完之后发现人家已经有开源了，下过来看了看发现我是用UIScrollerView的委托真是多此一举，完全可以用layout来实现嘛。我在判断重用的时候用了一大堆if没有别人写的简洁明了。

首先是定义委托，需要用户传入collection总item的总数与每一行中item的个数。其余的与UITableView的委托基本一致。

isNeedRefreshOrMore方法用来判断用户使用需要下拉刷新上拉更多的功能，返回YES就使用。

doCollectionRefresh即为响应下拉刷新事件。更多同样。。

 1 #pragma mark -
 2 #pragma mark 委托
 3 @protocol CustomCollectionDataSource<NSObject>
 4 @required
 5 //item的总个数
 6 -(NSInteger)numberOfItemsInCollection;
 7 //每一行的个数
 8 -(NSInteger)numberOfItemsInRow;
 9 @end
10 
11 @protocol CustomCollectionDelegate<NSObject>
12 @required
13 -(CustomCollectionItem *)itemInCollectionAtPoint:(CGPoint)point collectionView:(CustomCollectionView *)collection;
14 @optional
15 -(void)itemDidSelectedAtPoint:(CGPoint)point;
16 -(BOOL)isNeedRefreshOrMore;
17 -(void)doCollectionRefresh;
18 -(void)doCollectionMore;
19 
20 -(UIView *)collectionViewForHeader;
21 @end

在同文件中定义了页面状态的枚举，用来区分Collcetion的状态。同时定义了一些public方法

#import <UIKit/UIKit.h>

typedef enum {
    CS_Init,
    CS_More,
    CS_Refresh
}CollectionState;

@class CustomCollectionItem;
@protocol CustomCollectionDataSource;
@protocol CustomCollectionDelegate;

@interface CustomCollectionView : UIScrollView<UIScrollViewDelegate>
@property (weak, nonatomic) id<CustomCollectionDataSource> dataSource;
@property (weak, nonatomic) id<CustomCollectionDelegate> customDelegate;

-(CustomCollectionItem *)dequeueReusableItemWithIdentifier:(NSString *)identifier;
-(void)addItemsIntoDic;
-(void)itemClickedAtPoint:(CGPoint)point;
-(void)reloadData;
-(CustomCollectionItem *)getItemAtPoint:(CGPoint)point;

@property (strong,nonatomic) UIView *headerView;
@end

#import "CustomCollectionView.h"
#import "CustomCollectionItem.h"
#import "BaseRMView.h"
@interface CustomCollectionView()
//重用池--原谅这个名字
@property (strong, nonatomic) NSMutableDictionary *contentItemDictionary;
//能够显示的item数量（以行计）
@property(assign,nonatomic) NSInteger showCount;
@property (assign,nonatomic) NSInteger offRowIndex;
//分割线--没有用到 默认成了10px
@property (assign,nonatomic) CGFloat itemSpliteWidth;
//总行数
@property (assign,nonatomic) NSInteger rows;
//item个数
@property (assign, nonatomic) NSInteger numberOfItemsInCollection;
//每行item个数
@property (assign,nonatomic) NSInteger numberOfItemsInRow;
//每一行的高度
@property (assign, nonatomic) CGFloat heightOfRow;
//
@property (assign, nonatomic) CGRect viewFrame;
//是否第一次加载
@property (assign,nonatomic) BOOL isFirstLoad;
//上一次scrollview的offsetY，用来判断是向上滑动还是向下滑动
@property (assign,nonatomic) CGFloat lastOffsetY;
//当前最后一行的index，从0开始
@property (assign,nonatomic) NSInteger lastRowIndex;
//当前最上一行的index，从0开始
@property (assign,nonatomic) NSInteger topRowIndex;
//没用
@property (assign,nonatomic) NSInteger numberOfMore;
//是否需要显示刷新更多页面标志
@property (assign,nonatomic) BOOL isNeedShowMoreTag;
//刷新view
@property (strong,nonatomic) BaseRMView *refreshView;
//更多view
@property (strong,nonatomic) BaseRMView *moreView;

@property (assign,nonatomic) CGFloat baseOffsetY;
@property (assign,nonatomic) CGFloat baseCanMove;
//reload之前的行数，上拉更多的时候如果用户滑动的距离超过行高会出错，用beforeRowCount来比较rows来判断新增的item需要添加的坐标
@property (assign,nonatomic) NSInteger beforeRowCount;

//@property (assign,nonatomic) NSInteger firstShowCount;
@end

#pragma mark -
#pragma mark 页面初始化
-(id)init{
    CGRect frame=[UIScreen mainScreen].applicationFrame;
    self=[self initWithFrame:frame];
    if(self){
        
    }
    return self;
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        _viewFrame=frame;
        self.delegate=self;
        _isFirstLoad=YES;
        _contentItemDictionary=[[NSMutableDictionary alloc] init];
        _isNeedShowMoreTag=NO;
    }
    return self;
}

#pragma mark -
#pragma mark 数据初始化
-(void)loadData{
    if ([_dataSource respondsToSelector:@selector(numberOfItemsInCollection)]) {
        _numberOfItemsInCollection=[_dataSource numberOfItemsInCollection];
    }else{
        _numberOfItemsInCollection=0;
    }
    if([_dataSource respondsToSelector:@selector(numberOfItemsInRow)]){
        _numberOfItemsInRow=[_dataSource numberOfItemsInRow];
        _heightOfRow=((300.0-(_numberOfItemsInRow-1)*10)/_numberOfItemsInRow);
        _itemSpliteWidth=10;
    }else{
        _numberOfItemsInRow=3;//默认为3
        _heightOfRow=88;
        _itemSpliteWidth=18;
    }
    if ([_dataSource respondsToSelector:@selector(numberofMore)]) {
        _numberOfMore=[_dataSource numberofMore];
    }
    if ([_customDelegate respondsToSelector:@selector(isNeedRefreshOrMore)]) {
        _isNeedShowMoreTag=[_customDelegate isNeedRefreshOrMore];
    }
    if ([_customDelegate respondsToSelector:@selector(collectionViewForHeader)]) {
        _headerView=[_customDelegate collectionViewForHeader];
        if (![self.subviews containsObject:_headerView]) {
            [self addSubview:_headerView];
        }
    }
    //计算行数
    _rows=ceil((float)_numberOfItemsInCollection/_numberOfItemsInRow);
    CGFloat contentHeight=(_rows*_heightOfRow + (_rows+1)*10+_headerView.frame.size.height);
    CGFloat scrollContentHeight=contentHeight>_viewFrame.size.height?contentHeight:_viewFrame.size.height;
    //计算一页能显示多少行
    _showCount=  (NSInteger)ceil((self.frame.size.height/(_heightOfRow+10)));
    [self setContentSize:CGSizeMake(320, scrollContentHeight)];
    //判断是否有新增行，如果有当前最上义行index+1
    if (_rows!=_beforeRowCount&&_beforeRowCount!=0) {
        _topRowIndex++;
    }
　　//从当前最上一行开始增加showcount行的item
    for (int i=_topRowIndex; i<_topRowIndex+_showCount; i++) {
        [self creatItem:i];
    }
    if (_isNeedShowMoreTag==YES) {
        if (![self.subviews containsObject:_refreshView]) {
            _refreshView=[[BaseRMView alloc] initWithState:Refresh];
            [_refreshView setFrame:CGRectMake(0, -50, 320, 50)];
            [_refreshView setBackgroundColor:[UIColor grayColor]];
            [self addSubview:_refreshView];
        }

if (![self.subviews containsObject:_moreView]) {
            _moreView=[[BaseRMView alloc] initWithState:More];
            [_moreView setFrame:CGRectMake(0, self.contentSize.height, 320, 50)];
            [_moreView setBackgroundColor:[UIColor grayColor]];
            [self addSubview:_moreView];
        }else{
            [_moreView setFrame:CGRectMake(0, self.contentSize.height, 320, 50)];
        }
    }
}

-(void)layoutSubviews{
//第一次加载时初始化数据，之后不需要重新计算
    if (_isFirstLoad) {
        [self loadData];
        //offsetY基数 只在第一次移动时候，10为默认的分割线高度
        _baseOffsetY=(10*(_showCount+1)+_heightOfRow*_showCount)-self.frame.size.height;
        //移动基数
        _baseCanMove=10+_heightOfRow;
        _isFirstLoad=NO;
        _lastRowIndex=_showCount-1;
        _topRowIndex=0;
    }
}

//重新加载数据，记录加载前的行数
-(void)reloadData{
    _beforeRowCount=_rows;
    [self loadData];
}

#pragma mark -
#pragma mark Item相关
-(void)creatItem:(NSInteger)rowIndex{
    if ([_customDelegate respondsToSelector:@selector(itemInCollectionAtPoint:collectionView:)]) {
        for (int j=0; j<_numberOfItemsInRow; j++) {
            //判断当前个数是否超过了总个数（单数情况下）
            if (!(((rowIndex)*_numberOfItemsInRow+j+1)>_numberOfItemsInCollection)) {
                //根据委托创建item
                CustomCollectionItem *item=[_customDelegate itemInCollectionAtPoint:CGPointMake(rowIndex, j) collectionView:self];
                //设置item的大小
                [item setFrame:CGRectMake(10+_heightOfRow*j+_itemSpliteWidth*j, 10+_heightOfRow*rowIndex+10*rowIndex+_headerView.frame.size.height, _heightOfRow, _heightOfRow)];
                //设置item的point坐标
                item.point=CGPointMake(rowIndex, j);
                //在view中加入item
                [self addSubview:item];
            }
        }
    }
}

//根据重用标志（reuseidentifier）从重用池中获取item
-(CustomCollectionItem *)dequeueReusableItemWithIdentifier:(NSString *)identifier{
    NSArray *cellArray=[self.contentItemDictionary objectForKey:identifier];
    if (cellArray.count==0) {
        return nil;
    }else{
        id firstObject=[cellArray objectAtIndex:0];
        if([firstObject isKindOfClass:[CustomCollectionItem class]]){
            //获取item后从重用池中删除item;
            CustomCollectionItem *item=firstObject;
            [[self.contentItemDictionary objectForKey:identifier] removeObject:firstObject];
            [item reset];
            return item;
        }else{
            return nil;
        }
    }
}

//根据point坐标从当前item数组中获取item
-(CustomCollectionItem *)getItemAtPoint:(CGPoint)point{
    CustomCollectionItem *result=nil;
    for (id item in self.subviews) {
        if ([item isKindOfClass:[CustomCollectionItem class]]) {
            if (((CustomCollectionItem *)item).point.x==point.x
                && ((CustomCollectionItem *)item).point.y==point.y) {
                result=item;
            }
        }
    }
    return result;
}

-(void)addItemToPool:(CustomCollectionItem *)item{
    if([[self.contentItemDictionary allKeys] containsObject:item.reuseIdentifier]){
        [[self.contentItemDictionary objectForKey:item.reuseIdentifier] addObject:item];
    }else{
        NSMutableArray *cellArray=[NSMutableArray arrayWithObject:item];
        [self.contentItemDictionary setObject:cellArray forKey:item.reuseIdentifier];
    }
}

#pragma mark -
#pragma mark 页面滚动
//topRowIndex   ---> 当前最上一行的index(从0开始);
//lastRowIndex  ---> 当前最后一行的index
//removeIndex   ---> 当前被移除的最后一行的行数(从1开始)
//addIndex      ---> 在showcount基础上增加的行数
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
    @try {
        //手指向上移动移动基数后将显示下一页面
        //手指向下移动移动基数将移除最下一行
        BOOL isMoveUp=TRUE;//是否向下滑
        if (scrollView.contentOffset.y-_lastOffsetY>0) {
            isMoveUp=FALSE;
        }else{
            isMoveUp=TRUE;
        }
        _lastOffsetY=scrollView.contentOffset.y;
        
        //刷新更多
        if (scrollView.contentOffset.y==0) {
            if ([self.subviews containsObject:_refreshView]) {
                [_refreshView changeState:Refresh];
            }
        }else if(scrollView.contentOffset.y==scrollView.contentSize.height-scrollView.frame.size.height){
            if ([self.subviews containsObject:_moreView]) {
                [_moreView changeState:More];
            }
        }else if (scrollView.contentOffset.y>(scrollView.contentSize.height-scrollView.frame.size.height) ||
            scrollView.contentOffset.y<0) {
            if (scrollView.contentOffset.y>=(scrollView.contentSize.height-scrollView.frame.size.height+50)) {
                if ([self.subviews containsObject:_moreView]&&_moreView.viewState==More) {
                    [_moreView changeState:ToMore];
                }
            }else if (scrollView.contentOffset.y<-50){
                if ([self.subviews containsObject:_refreshView]&&_refreshView.viewState==Refresh) {
                    [_refreshView changeState:ToRefresh];
                }
            }
        }else{
            //判断重用
            if (scrollView.contentOffset.y>_headerView.frame.size.height) {
                CGFloat realMove=scrollView.contentOffset.y-_headerView.frame.size.height;
                //增加的row坐标 初始为0 移动一个移动基数后加/减1
                NSInteger addIndex=ceil((realMove-_baseOffsetY)/_baseCanMove);
                //删除的row坐标 初始为0 移动一个移动基数后加/减1
                NSInteger removeIndex=(realMove/_baseCanMove);
                
                //手指向上移动
                if (!isMoveUp) {
                    //如果最后一行编号==增加的row坐标+1&&增加的row坐标<总行数-1
                    if (_lastRowIndex==addIndex+_showCount-2&&addIndex<_rows-1) {
                        //最后一行坐标++
                        _lastRowIndex++;
                        //如果最后一行坐标！=总行数；如果相等则为最后一行不需要增加
                        if (_lastRowIndex!=_rows) {
                            [self creatItem:_lastRowIndex];
                        }
                    }
                    //如果删除的row坐标！=0&&删除的row坐标！=最上一行坐标&&最上一行坐标<总行数-显示行数
                    if (removeIndex!=0&&removeIndex!=_topRowIndex&&_topRowIndex<_rows-_showCount) {
                        for (int i=0; i<_numberOfItemsInRow; i++) {
                            CustomCollectionItem *item=[self getItemAtPoint:CGPointMake(removeIndex-1, i)];
                            if (item!=nil) {
                                [self addItemToPool:item];
                                [item removeFromSuperview];
                            }
                        }
                        _topRowIndex++;
                    }
                }else{//remove-->add add-->remove
                    if (removeIndex==_topRowIndex-1) {
                        [self creatItem:removeIndex];
                        _topRowIndex--;
                    }
                    if (addIndex!=0&&addIndex!=_lastRowIndex-_showCount+1) {
                        if (_lastRowIndex==_rows) {
                            _lastRowIndex--;
                        }else{
                            for (int i=0; i<_numberOfItemsInRow; i++) {
                                CustomCollectionItem *item=[self getItemAtPoint:CGPointMake(_lastRowIndex, i)];
                                if (item!=nil) {
                                    [self addItemToPool:item];
                                    [item removeFromSuperview];
                                }
                            }
                            _lastRowIndex--;
                        }
                    }
                }
            }
        }
    }
    @catch (NSException *exception) {
        NSLog(@"customCollectionView exception %@",exception.reason);
    }
}

#pragma mark-
#pragma mark item点击
-(void)itemClickedAtPoint:(CGPoint)point{
    if ([_customDelegate respondsToSelector:@selector(itemDidSelectedAtPoint:)]) {
        [_customDelegate itemDidSelectedAtPoint:point];
    }
}

#pragma mark-
#pragma mark 刷新更多

-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
    if (scrollView.contentOffset.y<-50) {
        if (_isNeedShowMoreTag==YES&&[self.subviews containsObject:_refreshView]) {
            if ([_customDelegate respondsToSelector:@selector(doCollectionRefresh)]) {
                [_customDelegate doCollectionRefresh];
            }
            [_refreshView changeState:EndRefresh];
        }
    }else if (scrollView.contentOffset.y>scrollView.contentSize.height-scrollView.frame.size.height+50){
        if (_isNeedShowMoreTag==YES&&[self.subviews containsObject:_moreView]) {
            if ([_customDelegate respondsToSelector:@selector(doCollectionMore)]) {
                [_customDelegate doCollectionMore];
            }
            [_moreView changeState:EndMore];
        }
    }
}

#import <UIKit/UIKit.h>
#import <objc/runtime.h>
#import <Foundation/Foundation.h>
@interface CustomCollectionItem : UIView<UIGestureRecognizerDelegate,NSCoding>
@property (strong,nonatomic) UIImageView *backgroundImage;
@property (strong,nonatomic) NSString *reuseIdentifier;
@property (assign,nonatomic) CGPoint point;
-(id)initWithReuseIdentifier:(NSString *)identifier;
-(void)itemTaped;
-(void)reset;
@end

#import "CustomCollectionItem.h"
#import "CustomCollectionView.h"

@interface CustomCollectionItem()
@property(strong,nonatomic) UIView *contentView;
@end

@implementation CustomCollectionItem

-(id)initWithReuseIdentifier:(NSString *)identifier{
    self=[super init];
    if (self) {
        _reuseIdentifier=identifier;
        [self setUserInteractionEnabled:YES];
        _backgroundImage= [[UIImageView alloc] init];
    }
    return self;
}

-(void)setFrame:(CGRect)frame {
    [super setFrame:frame];
    [_backgroundImage setFrame:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
    _backgroundImage.tag=10099;
}

-(void)layoutSubviews {
    [super layoutSubviews];
    if([self viewWithTag:10099]== nil)   {
        [self addSubview:_backgroundImage];
        [self sendSubviewToBack:_backgroundImage];
    }
    UITapGestureRecognizer *tapGR=[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(itemTaped)];
    [self addGestureRecognizer:tapGR];
}

-(void)itemTaped{
    [(CustomCollectionView *)[self superview] itemClickedAtPoint:self.point];
}

-(void)setBackgroundImage:(UIImageView *)backgroundImage {
    _backgroundImage=backgroundImage;
}

#pragma override
-(void)reset{
    
}

- (void)encodeWithCoder:(NSCoder*)coder
{
    Class clazz = [self class];
    u_int count;
    
    objc_property_t* properties = class_copyPropertyList(clazz, &count);
    NSMutableArray* propertyArray = [NSMutableArray arrayWithCapacity:count];
    for (int i = 0; i < count ; i++)
    {
        const char* propertyName = property_getName(properties[i]);
        [propertyArray addObject:[NSString  stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
    }
    free(properties);
    
    
    for (NSString *name in propertyArray)
    {
        id value = [self valueForKey:name];
        [coder encodeObject:value forKey:name];
    }
}

- (id)initWithCoder:(NSCoder*)decoder
{
    if (self = [super init])
    {
        if (decoder == nil)
        {
            return self;
        }
        
        Class clazz = [self class];
        u_int count;
        
        objc_property_t* properties = class_copyPropertyList(clazz, &count);
        NSMutableArray* propertyArray = [NSMutableArray arrayWithCapacity:count];
        for (int i = 0; i < count ; i++)
        {
            const char* propertyName = property_getName(properties[i]);
            [propertyArray addObject:[NSString  stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
        }
        free(properties);
        
        
        for (NSString *name in propertyArray)
        {
            id value = [decoder decodeObjectForKey:name];
            [self setValue:value forKey:name];
        }
    }
    return self;
}
@end

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原文地址：https://www.cnblogs.com/LifeTechnologySupporter/p/5037806.html