[笔记][08723] 使用 AssetsLibrary 得到 Camera Roll 中的 Assets

源代码下载：https://github.com/1992chenlu/AssetsLibraryDemo

这个demo主要针对作业的第一个要求： showing all the multimedia files from Photo Album in a table view。需要用到 AssetsLibrary 来得到当前 Camera Roll 中所有的Asset，然后显示在 TableView 里面。

（注意：在这个demo里TableView 中显示的是所有的 video，而苏菲的要求是 all the multimedia files，也就是要包括 photos，实现方法见代码注释，友情建议：测试photo显示时，请先清一清自己之前的自拍，泪奔T_T）

另外，最好将 TableViewController 嵌在 Navigation Controller 里面使用（之前 第一版 里面没有这么做，现在补上了），因为后面加segue跳转到下一屏显示video或image的时候，必须要有 Navigation Controller才能实现跳转，只使用 TableViewController 是无法实现页面跳转的。

效果图：

步骤：

1. 新建一个工程，删掉 storyboard 中 default 的 ViewController，加入一个NavigationController，并设为 initial view controller。

2. 新建一个  UITableViewController 的 subclass，命名为 MyTableViewController。并将MyTableViewController 设为 Storyboard 中刚刚添加的 Root View Controller 的 Custom Class。

3. 不废话了，码代码。

//
//  MyTableViewController.h
//  AssetLibraryDemo
//
//  Created by 鲁辰 on 7/5/15.
//  Copyright (c) 2015 ChenLu. All rights reserved.
//

#import <UIKit/UIKit.h>
#import <AssetsLibrary/AssetsLibrary.h>
#import <AVFoundation/AVFoundation.h>

@interface MyTableViewController : UITableViewController<UITableViewDataSource, UITableViewDelegate>

@property (nonatomic, strong) ALAssetsLibrary *assetsLibrary;
@property (nonatomic, strong) NSMutableArray *videoTitleArray;
@property (nonatomic, strong) NSMutableArray *videoURLArray;
@property (nonatomic, strong) NSMutableArray *videoImageArray;

@end

//
//  MyTableViewController.m
//  AssetLibraryDemo
//
//  Created by 鲁辰 on 7/5/15.
//  Copyright (c) 2015 ChenLu. All rights reserved.
//

#import "MyTableViewController.h"

@implementation MyTableViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
}

- (void) viewWillAppear:(BOOL)animated  {
    _videoTitleArray = [[NSMutableArray alloc] init];
    _videoURLArray = [[NSMutableArray alloc] init];
    _videoImageArray = [[NSMutableArray alloc] init];
    [self buildAssetsLibrary];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table View Data source
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:
(NSInteger)section{
    return _videoTitleArray.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:
(NSIndexPath *)indexPath{
    static NSString *cellIdentifier = @"cellID";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:
                             cellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc]initWithStyle:
                UITableViewCellStyleValue1 reuseIdentifier:cellIdentifier];
    }
    
    NSString *stringForCell;
    stringForCell= [_videoTitleArray objectAtIndex:indexPath.row];
    [cell.textLabel setText:stringForCell];
    cell.imageView.image = [_videoImageArray objectAtIndex:indexPath.row];
    return cell;
}

#pragma mark - Show Video List Methods
- (void)buildAssetsLibrary
{
    _assetsLibrary = [[ALAssetsLibrary alloc] init];
    ALAssetsLibrary *notificationSender = nil;
    
    NSString *minimumSystemVersion = @"4.1";
    NSString *systemVersion = [[UIDevice currentDevice] systemVersion];
    if ([systemVersion compare:minimumSystemVersion options:NSNumericSearch] != NSOrderedAscending)
        notificationSender = _assetsLibrary;
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(assetsLibraryDidChange:) name:ALAssetsLibraryChangedNotification object:notificationSender];
    [self updateAssetsLibrary];
}

- (void)assetsLibraryDidChange:(NSNotification*)changeNotification
{
    [self updateAssetsLibrary];
}

- (void)updateAssetsLibrary
{
    ALAssetsLibrary *assetLibrary = _assetsLibrary;
    
    [assetLibrary enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop)
     {
         if (group)
         {
             [group setAssetsFilter:[ALAssetsFilter allVideos]];
             //Please see: https://developer.apple.com/library/ios/documentation/AssetsLibrary/Reference/ALAssetsFilter_Class/
             //To get all assets (photos and videos), use allAssets as filter.
             
             [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop)
              {
                  if (asset)
                  {
                      ALAssetRepresentation *defaultRepresentation = [asset defaultRepresentation];
                      NSString *uti = [defaultRepresentation UTI];
                      NSURL *videoURL = [[asset valueForProperty:ALAssetPropertyURLs] valueForKey:uti];
                      
                      NSString *title = [NSString stringWithFormat:@"%@", NSLocalizedString(@"Video", nil)];
                      [_videoTitleArray addObject:title];
                      [_videoURLArray addObject:videoURL];
                      
                      CGImageRef thumbnailImageRef = [asset thumbnail];
                      UIImage *thumbnail = [UIImage imageWithCGImage:thumbnailImageRef];
                      [_videoImageArray addObject:thumbnail];
                      [self.tableView reloadData];
                  }
              } ];
         }
     }
                              failureBlock:^(NSError *error)
     {
         NSLog(@"error enumerating AssetLibrary groups %@\n", error);
     }];
}

@end

Reference：

http://stackoverflow.com/questions/17585908/how-can-i-get-the-list-of-all-video-files-from-library-in-ios-sdk