ALAssetsLibrary从ALAssetsGroupAll加载单张照片

Question

我试图构建一个类似于iOS 7的照片应用的自定义图像选择器。我能够从相机胶卷中挑选一张照片（ALAssetsGroupSavedPhotos），但我很难从另一张相册中加载单张图像 - 我为测试目的而创建的一张相册。

下面是我使用的加载从相机胶卷照片的代码：

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init]; 

[library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) { 

    [group setAssetsFilter:[ALAssetsFilter allPhotos]]; 
    numberOfPhotos = [group numberOfAssets]; 

    [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:index] options:0 usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) { 


          if (alAsset) { 

           ALAssetRepresentation *representation = [alAsset defaultRepresentation]; 
           UIImage *lastImage = [UIImage imageWithCGImage:[representation fullScreenImage]]; 


          } 

         }]; 

} 
        failureBlock: ^(NSError *error2) { 


        }]; 

我试图取代ALAssetsGroupSavedPhotos与ALAssetsGroupAll但它返回以下错误：

Terminating app due to uncaught exception 'NSRangeException', reason: 'indexSet count or lastIndex must not exceed -numberOfAssets'

Answer 1

你正在枚举库中的所有文件夹并试图从每个文件夹中获取照片。这是错误的。首先你必须得到你的文件夹。

__block ALAssetsGroup* folder; 
NSString *yourFolderName = ...; 

[library enumerateGroupsWithTypes:ALAssetsGroupAlbum 
          usingBlock:^(ALAssetsGroup *group, BOOL *stop) 
{ 
     if ([[group valueForProperty:ALAssetsGroupPropertyName] isEqualToString:yourFolderName]) 
     { 
      folder = group; 
     } 
} 
          failureBlock:^(NSError* error) 
{ 
    // Error handling.  
}]; 

然后，从文件夹中获得的图像：

[group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:index] 
         options:0 
        usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) 
{ 
    if (alAsset) 
    { 
     ALAssetRepresentation *representation = [alAsset defaultRepresentation]; 
     UIImage *lastImage = [UIImage imageWithCGImage:[representation fullScreenImage]]; 
    } 
}]; 

但要确保index是正确的。