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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]];}
UICollectionView基础