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.