ALAsset

获得的ALAsset对象就是相片对象：其中有相片的缩略图，全屏图，高清图，url等属性。

ALAsset *result = [assets objectAtIndex:index];

获取url：

String类型：

NSString *url = [[[result

defaultRepresentation]url]description];

URL类型：

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

获取缩略图：

CGImageRef ref = [result thumbnail];

UIImage *img = [[UIImage alloc]initWithCGImage:ref];

获取全屏相片：

CGImageRef ref = [[result defaultRepresentation]fullScreenImage];

UIImage *img = [[UIImage alloc]initWithCGImage:ref];

获取高清相片：

CGImageRef ref = [[result defaultRepresentation]fullResolutionImage];

UIImage *img = [[UIImage alloc]initWithCGImage:ref];