• UICollectionView使用注意點(diǎn)

• 創(chuàng)建UICollectionView必須要有布局參數(shù)

• cell必須通過(guò)注冊(cè)

• cell必須自定義,系統(tǒng)cell沒(méi)有任何子控件

• 示例

#import "ViewController.h"
#import "PhotoCell.h"
@interface ViewController ()<UICollectionViewDataSource>

@end
static NSString * const ID = @"cell";

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //函數(shù)式編程思想(高聚合):把很多功能放在一個(gè)函數(shù)塊(block塊)去處理 多見(jiàn)于swift
    UICollectionViewFlowLayout *layout = ({
        UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc]init];
        //設(shè)置水平滾動(dòng)
        layout.scrollDirection  =  UICollectionViewScrollDirectionHorizontal;
        //設(shè)置cell的尺寸
        layout.itemSize = CGSizeMake(160, 160);
        CGFloat margin = ([UIScreen mainScreen].bounds.size.width - 160) *0.5;
        //設(shè)置內(nèi)邊距
        layout.sectionInset = UIEdgeInsetsMake(0, margin, 0, margin);
        //設(shè)置最小行間距
        layout.minimumLineSpacing = 50;
        layout;
    });
    UICollectionView *collectionView = ({
        UICollectionView *collectionView = [[UICollectionView alloc]initWithFrame:CGRectZero collectionViewLayout:layout];
        collectionView.backgroundColor = [UIColor blueColor];
        collectionView.center = self.view.center;
        collectionView.bounds =CGRectMake(0, 0, self.view.bounds.size.width, 200);
        [self.view addSubview:collectionView];
        collectionView;
        
    });
    
    //關(guān)閉水平滾動(dòng)條
    collectionView.showsHorizontalScrollIndicator = NO;
    collectionView.dataSource = self;
    //注冊(cè)nib
    [collectionView registerNib:[UINib nibWithNibName:NSStringFromClass([PhotoCell class]) bundle:nil] forCellWithReuseIdentifier:ID];
    
}
//有多少個(gè)cell
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 10;
}
//cell樣式
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    PhotoCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:ID forIndexPath:indexPath];
    NSString *imageName = [NSString stringWithFormat:@"%ld",indexPath.item + 1];
    cell.image = [UIImage imageNamed:imageName];
    return cell;
}
@end

• UICollectionViewFlowLayout自定義布局

  • UICollectionViewFlowLayout自定義布局必須知道的5個(gè)方法

// 何時(shí)調(diào)用:collectionView第一次布局,collectionView刷新的時(shí)候也會(huì)調(diào)用
// 作用:計(jì)算cell的布局,條件:cell的位置是固定不變
 - (void)prepareLayout
{
    [super prepareLayout];

}
// 作用:指定一段區(qū)域給你這段區(qū)域內(nèi)cell的尺寸
// 可以一次性返回所有cell尺寸,也可以每隔一個(gè)距離返回cell
/**
 UICollectionViewLayoutAttributes:確定cell的尺寸
 一個(gè)UICollectionViewLayoutAttributes對(duì)象就對(duì)應(yīng)一個(gè)cell
 拿到UICollectionViewLayoutAttributes相當(dāng)于拿到cell
 */
- (nullable NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *attrs = [super layoutAttributesForElementsInRect:CGRectMake(0, 0, MAXFLOAT, MAXFLOAT)];
    return attrs;
    
}
// 何時(shí):用戶(hù)手指一松開(kāi)就會(huì)調(diào)用
// 作用:確定最終偏移量
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity{

    // 拖動(dòng)比較快 最終偏移量 不等于 手指離開(kāi)時(shí)偏移量
    
    // 最終偏移量
    CGPoint targetP = [super targetContentOffsetForProposedContentOffset:proposedContentOffset withScrollingVelocity:velocity];
    
    // 獲取collectionView偏移量
    NSLog(@"%@ %@",NSStringFromCGPoint(targetP),NSStringFromCGPoint(self.collectionView.contentOffset));
    
    return CGPointZero;
}

// Invalidate:刷新
// 在滾動(dòng)的時(shí)候是否允許刷新布局
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
    return YES;
}
// 計(jì)算collectionView滾動(dòng)范圍
- (CGSize)collectionViewContentSize{
    return [super collectionViewContentSize];
}

demo