选中系统照片库中多张照片的方法

//
//  ViewController.m
//  SelectMorePhoto
//
//  Created by phc on 16/7/17.
//  Copyright © 2016年 phc. All rights reserved.
//

#import "ViewController.h"
#import <AssetsLibrary/AssetsLibrary.h>
#import <Photos/Photos.h>
@interface ViewController ()<UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>
@property(nonatomic,strong)NSMutableArray *imgArr;
@property (strong, nonatomic) UICollectionView *collectionView;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    
    _imgArr = [NSMutableArray array];
    //1.创建资源库对象(资源库中包含所有的视频和照片)
      ALAssetsLibrary * library = [[ALAssetsLibrary alloc] init];
     //遍历资源库
      [library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
          //ALAssetsGroup代表资源库中的一个相册
          if (group) {//如果存在,在遍历
               //遍历相册中的所有的资源(包括照片,和视频)
              [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                  /*
                  if (index == 3) {
                      
                      *stop = YES;
                  }
                  */
                 //ALAsset代表一个照片
                //获取图片的缩略图
                 CGImageRef cimg = [result thumbnail];
                 UIImage *img = [UIImage imageWithCGImage:cimg];
                  //容错
                  if (img) {
                      
                      [_imgArr addObject:img];
                  }
              }];
          }
      [_collectionView reloadData];
          
      } failureBlock:^(NSError *error) {
          
          NSLog(@"访问失败");
      }];
    
    [self creactCollection];
    
}

- (void)creactCollection{
    
    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    
    //设置单元格尺寸
    flowLayout.itemSize = CGSizeMake(70, 70);
    _collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:flowLayout];
    _collectionView.backgroundColor = [UIColor greenColor];
    //设置代理方法和数据源方法
    _collectionView.delegate = self;
    _collectionView.dataSource = self;
    
    [self.view addSubview:_collectionView];
    
    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cell"];
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    
    return _imgArr.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
    
    UIImageView *imgView = [[UIImageView alloc] initWithFrame:cell.bounds];
    imgView.backgroundColor = [UIColor redColor];
    [cell.contentView addSubview:imgView];
    imgView.image = _imgArr[indexPath.row];
    
    return cell;
       
}


@end