UICollectionView具体解释

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怎样显示在界面上，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。其可定制的内容例如以下：

itemSize属性

设定全局的Cell尺寸。假设想要单独定义某个Cell的尺寸，能够使用以下方法：

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

minimumLineSpacing属性

设定全局的行间距，假设想要设定指定区内Cell的最小行距，能够使用以下方法：

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

minimumInteritemSpacing属性

设定全局的Cell间距，假设想要设定指定区内Cell的最小间距，能够使用以下方法：

- (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，须要注意的是，依据滚动方向不同，header和footer的width和height中仅仅有一个会起作用。假设要单独设置指定区内的页面和页脚尺寸，能够使用以下方法：

- (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。假设想要设定指定区的内边距，能够使用以下方法：

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

---

然后须要实现三种类型的托付：UICollectionViewDataSource, UICollectionViewDelagate和UICollectionViewDelegateFlowLayout。

@interface ViewController : UIViewController <UICollectionViewDelegateFlowLayout, UICollectionViewDataSource>

由于UICollectionViewDelegateFlowLayout实际上是UICollectionViewDelegate的一个子协议。它继承了UICollectionViewDelegate。所以仅仅须要在声明处写上UICollectionViewDelegateFlowLayout即可了。

---

UICollectionViewDataSource

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView

返回collection view里区(section)的个数，假设没有实现该方法，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)包括的数据源条目数(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相应的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结构上相对照较简单。由下至上：

• 首先是cell本身作为容器view
• 然后是一个大小自己主动适应整个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，自己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加入一个补充视图(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

加入页眉和页脚曾经须要注冊类和标识：

---

加入补充视图的代码演示样例：

[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

在注冊Cell和补充视图时。也能够用新建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"];

用这样的方式注冊后，甚至能够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。也能够直接设置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，也能够直接设置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. 当你删除或加入元素时。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，仅在同意多选时被调用

以下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

事件的处理顺序例如以下：

1. 手指按下
2. shouldHighlightItemAtIndexPath (假设返回YES则向下运行。否则运行到这里为止)
3. didHighlightItemAtIndexPath (高亮)
4. 手指松开
5. didUnhighlightItemAtIndexPath (取消高亮)
6. shouldSelectItemAtIndexPath (假设返回YES则向下运行，否则运行到这里为止)
7. didSelectItemAtIndexPath (运行选择事件)

假设仅仅是简单实现点击后cell改变显示状态，仅仅须要在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;
}

假设要实现点击时(手指未松开)的显示状态与点击后(手指松开)的显示状态。则须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]];
}