UICollectionView基础

初始化部分：

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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];
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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：

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-(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;
}
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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：

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[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;
}
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MyHeadView.h

#import <UIKit/UIKit.h>

@interface MyHeadView : UICollectionReusableView

• (void) setLabelText:(NSString *)text;
  @end

  MyHeadView.m

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  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
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  在注册Cell和补充视图时，也可以用新建xib文件的方式：

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  [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"];
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  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

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  -(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);
  }

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

  设定collectionView(指定区)的边距

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  -(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);
  }

  }
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  -(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

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

  if(section==0)
  {
      return 10.0;
  }
  else
  {
      return 20.0;
  }

  }
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  -(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

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

  if(section==0)
  {
      return 10.0;
  }
  else
  {
      return 20.0;
  }

  }
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  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：

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  -(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;

  }
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  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：

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  -(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]];

  }