通过创建ALAssetsLibrary 的实例可以访问系统Photos里的图片与视频。这个库包括了保存的图片，从iTunes导入的和从其他设备里面导入的图片，你可以访问所有的分类和保存图片视频。

用普通的alloc和init就可以创建ALAssetsLibrary的实例，所有你从这个实例中获取得到的对象的生命周期和ALAssetsLibrary这个实例的生命周期一致。

大多数的函数，都是异步处理的，所有的成功失败的回调都是使用block传入的，因为有可能需要用户点击授权。在iOS4至iOS5的版本中，会提示要访问用户的地理位置。到iOS6会提示访问用户的照片信息，这一点需要注意。

可以遍历Group,创建Group，创建图片，添加信息等，可以进行大多数的访问与操作。

可以通过valueForProperty获取到图片的信息，包括类型， Location , 时长，方向，日期，格式 ， URL地址。

NSString * nsALAssetPropertyType = [ asset valueForProperty:ALAssetPropertyType ] ;

NSString * nsALAssetPropertyLocation = [ asset valueForProperty:ALAssetPropertyLocation ] ;

NSString * nsALAssetPropertyDuration = [ asset valueForProperty:ALAssetPropertyDuration ] ;

NSString * nsALAssetPropertyOrientation = [ asset valueForProperty:ALAssetPropertyOrientation ] ;

NSString * nsALAssetPropertyDate = [ asset valueForProperty:ALAssetPropertyDate ] ;

NSString * nsALAssetPropertyRepresentations = [ asset valueForProperty:ALAssetPropertyRepresentations ] ;

NSString * nsALAssetPropertyURLs = [ asset valueForProperty:ALAssetPropertyURLs ] ;

NSString * nsALAssetPropertyAssetURL = [ asset valueForProperty:ALAssetPropertyAssetURL ] ;

获取全部图片的示例：

//View Controller header(.h) file..

#import <UIKit/UIKit.h>

#include<AssetsLibrary/AssetsLibrary.h>

@interface getPhotoLibViewController : UIViewController

{

ALAssetsLibrary *library;

NSArray *imageArray;

NSMutableArray *mutableArray;

}

-(void)allPhotosCollected:(NSArray*)imgArray;

@end

//implementation file

declare global count variable as

static int count=0;

@implementation getPhotoLibViewController

-(void)getAllPictures

{

imageArray=[[NSArray alloc] init];

mutableArray =[[NSMutableArray alloc]init];

NSMutableArray* assetURLDictionaries = [[NSMutableArray alloc] init];

library = [[ALAssetsLibrary alloc] init];

void (^assetEnumerator)( ALAsset *, NSUInteger, BOOL *) = ^(ALAsset *result, NSUInteger index, BOOL *stop) {

if(result != nil) {

if([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto]) {

[assetURLDictionaries addObject:[result valueForProperty:ALAssetPropertyURLs]];

NSURL *url= (NSURL*) [[result defaultRepresentation]url];

[library assetForURL:url

resultBlock:^(ALAsset *asset) {

[mutableArray addObject:[UIImage imageWithCGImage:[[asset defaultRepresentation] fullScreenImage]]];

if ([mutableArray count]==count)

{

imageArray=[[NSArray alloc] initWithArray:mutableArray];

[self allPhotosCollected:imageArray];

}

}

failureBlock:^(NSError *error){ NSLog(@"operation was not successfull!"); } ];

}

}

};

NSMutableArray *assetGroups = [[NSMutableArray alloc] init];

void (^ assetGroupEnumerator) ( ALAssetsGroup *, BOOL *)= ^(ALAssetsGroup *group, BOOL *stop) {

if(group != nil) {

[group enumerateAssetsUsingBlock:assetEnumerator];

[assetGroups addObject:group];

count=[group numberOfAssets];

}

};

assetGroups = [[NSMutableArray alloc] init];

[library enumerateGroupsWithTypes:ALAssetsGroupAll

usingBlock:assetGroupEnumerator

failureBlock:^(NSError *error) {NSLog(@"There is an error");}];

}

-(void)allPhotosCollected:(NSArray*)imgArray

{

//write your code here after getting all the photos from library...

NSLog(@"all pictures are %@",imgArray);

}

@end

Use getAllPicture method to get photos from photo library.