UICollectionViewController在使用之前必须要做的两件事:

一. 为UICollectionViewController指定布局方式

二. 为UICollectionViewController注册单元格

流式布局小例子:

#import "SZMProductCollectionViewController.h"#import "SZMProductModel.h"#import "SZMProductCell.h"@interface SZMProductCollectionViewController ()@property (nonatomic,strong)NSArray *products;@end@implementation SZMProductCollectionViewControllerstatic NSString * const reuseIdentifier = @"Cell";- (NSArray *)products{    if (!_products) {        //加载数据                //获取json文件路径        NSString *path = [[NSBundle mainBundle]pathForResource:@"more_project.json" ofType:nil];        //把json文件加载到一个NSData对象中        NSData *jsonData = [NSData dataWithContentsOfFile:path];        //把NSData转换为一个字典数组        NSArray *arrayDicts = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:nil];        //把字典数组转换为一个模型数组        NSMutableArray *modelArray = [NSMutableArray array];        for (NSDictionary *dict in arrayDicts) {            SZMProductModel *modle = [SZMProductModel productWithDict:dict];            [modelArray addObject:modle];        }        _products = modelArray;    }    return _products;}- (instancetype)init{    //创建一个流式布局对象    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc]init];    //设置每个cell的大小    layout.itemSize = CGSizeMake(80, 80);    //设置每个cell间的最小水平间距    layout.minimumInteritemSpacing = 0;    //设置每个cell间的行间距    layout.minimumLineSpacing = 5;    //设置每一组距离四周的内边距    layout.sectionInset = UIEdgeInsetsMake(5, 0, 0, 0);        //返回    return [super initWithCollectionViewLayout:layout];    }- (void)viewDidLoad {    [super viewDidLoad];    //注册类:注册单元格:告诉系统(UICollectionView),当缓存池中没有现成的cell对象以后,要创建哪个类的对象作为cell来使用    //[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:reuseIdentifier];        //注册xib    UINib *nib = [UINib nibWithNibName:@"SZMProductCell" bundle:nil];    [self.collectionView registerNib:nib forCellWithReuseIdentifier:reuseIdentifier];        [self.collectionView setBackgroundColor:[UIColor colorWithPatternImage:[UIImage imageNamed:@"bg"]]];    }- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{        SZMProductModel *model = self.products[indexPath.row];    NSLog(@"%@",model.title);}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}#pragma mark 
     
      //返回多少组- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {    return 1;}//每组返回多少格子- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {    return self.products.count;}//每个格子返回什么内容- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {        //1.获取数据    SZMProductModel *model = self.products[indexPath.row];    //2.创建cell    SZMProductCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];    //3.为cell设置数据    cell.product = model;            return cell;}@end