UICollectionView基礎

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決定了UICollectionView如何顯示在界面上，Apple提供了一個最簡單的默認layout對象：UICollectionViewFlowLayout。

Flow Layout是一個Cells的線性佈局方案，並具備頁面和頁腳。其可定製的內容以下：

itemSize屬性

設定全局的Cell尺寸，若是想要單獨定義某個Cell的尺寸，可使用下面方法：

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

minimumLineSpacing屬性

設定全局的行間距，若是想要設定指定區內Cell的最小行距，可使用下面方法：

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

minimumInteritemSpacing屬性

設定全局的Cell間距，若是想要設定指定區內Cell的最小間距，可使用下面方法：

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

scrollDirection屬性

設定滾動方向，有UICollectionViewScrollDirectionVertical和UICollectionViewScrollDirectionHorizontal兩個值。

headerReferenceSize屬性與footerReferenceSize屬性

設定頁眉和頁腳的全局尺寸，須要注意的是，根據滾動方向不一樣，header和footer的width和height中只有一個會起做用。若是要單獨設置指定區內的頁面和頁腳尺寸，可使用下面方法：

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

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

sectionInset屬性

設定全局的區內邊距，若是想要設定指定區的內邊距，可使用下面方法：

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

 

而後須要實現三種類型的委託：UICollectionViewDataSource, UICollectionViewDelagate和UICollectionViewDelegateFlowLayout。

@interface ViewController : UIViewController <UICollectionViewDelegateFlowLayout, UICollectionViewDataSource>
由於UICollectionViewDelegateFlowLayout其實是UICollectionViewDelegate的一個子協議，它繼承了UICollectionViewDelegate，因此只須要在聲明處寫上UICollectionViewDelegateFlowLayout就好了。

 

UICollectionViewDataSource

-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView

返回collection view裏區(section)的個數，若是沒有實現該方法，將默認返回1：

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

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

返回指定區(section)包含的數據源條目數(number of items)，該方法必須實現：

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

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

返回某個indexPath對應的cell，該方法必須實現：

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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結構上相對比較簡單，由下至上：

首先是cell自己做爲容器view
而後是一個大小自動適應整個cell的backgroundView，用做cell平時的背景
再其次是selectedBackgroundView，是cell被選中時的背景
最後是一個contentView，自定義內容應被加在這個view上
 

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

爲collection view添加一個補充視圖(頁眉或頁腳)

 

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

設定頁眉的尺寸

 

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

設定頁腳的尺寸

 

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

添加頁眉和頁腳之前須要註冊類和標識：

 

添加補充視圖的代碼示例：

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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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  在註冊Cell和補充視圖時，也能夠用新建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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  用這種方式註冊後，甚至能夠不用新建類去綁定這個xib，直接經過viewWithTag的方式獲取xib裏的控件：

  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

  設定指定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;

  設定collectionView(指定區)的邊距

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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

  設定指定區內Cell的最小行距，也能夠直接設置UICollectionViewFlowLayout的minimumLineSpacing屬性

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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;

  設定指定區內Cell的最小間距，也能夠直接設置UICollectionViewFlowLayout的minimumInteritemSpacing屬性

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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

  當指定indexPath處的item被選擇時觸發

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

  [collectionView deleteItemsAtIndexPaths:[NSArray arrayWithObject:indexPath]];
  }
  P.s. 當你刪除或添加元素時，必定要更新numberOfItemsInSection的返回狀況。

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

  當指定indexPath處的item被取消選擇時觸發，僅在容許多選時被調用

  下面是三個和高亮有關的方法：

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

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

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

  事件的處理順序以下：

  手指按下
  shouldHighlightItemAtIndexPath (若是返回YES則向下執行，不然執行到這裏爲止)
  didHighlightItemAtIndexPath (高亮)
  手指鬆開
  didUnhighlightItemAtIndexPath (取消高亮)
  shouldSelectItemAtIndexPath (若是返回YES則向下執行，不然執行到這裏爲止)
  didSelectItemAtIndexPath (執行選擇事件)
  若是隻是簡單實現點擊後cell改變顯示狀態，只須要在cellForItemAtIndexPath方法裏返回cell時，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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  若是要實現點擊時(手指未鬆開)的顯示狀態與點擊後(手指鬆開)的顯示狀態，則須要經過上面提到的方法來實現：

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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]];

  }