ios - Objective-C/ALAssetLibrary - 如何读取和保存有关图像的信息

Question

我使用 ALAssetLibrary 在我的模拟器中找到了一些关于图像的信息。我可以使用 NSLog 正确显示这些信息，但我不知道如何将这些信息保存在列表中。我使用的代码是这样的:

NSMutableArray *list = [[NSMutableArray alloc] init];
ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    if (group) {
        [group setAssetsFilter:[ALAssetsFilter allPhotos]];
        [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop){
            if (asset){
                NSString *description = [asset description];
                NSRange first = [description rangeOfString:@"URLs:"];
                NSRange second = [description rangeOfString:@"?id="];
                NSString *path = [description substringWithRange: NSMakeRange(first.location + first.length, second.location - (first.location + first.length))];
                NSLog(@"Path: %@", path);
                [list addObject:path];
                NSDictionary *data = [[asset defaultRepresentation] metadata];
                NSNumber *width = [[[asset defaultRepresentation] metadata] objectForKey:@"PixelWidth"];
                NSString *widthString = [NSString stringWithFormat:@"%@", width];
            }
        }];
    }
} failureBlock:^(NSError *error) {
    NSLog(@"error enumerating AssetLibrary groups %@\n", error);
}];
NSLog(@"LIST: %@", list);

据我所知，这些操作是异步进行的，所以我不知道如何保存它们。有什么想法吗？

谢谢

Answer 1

为什么不直接创建一个可变数组，并在每次通过枚举时将您关心的值导出到数组中。这样，您将拥有一个易于访问的项目索引列表。这是一个例子:

NSMutableArray *myContainerArray = [NSMutableArray new];

ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    if (group) {
        [group setAssetsFilter:[ALAssetsFilter allPhotos]];
        [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop){
            if (asset){
                NSString *description = [asset description];
                NSRange first = [description rangeOfString:@"URLs:"];
                NSRange second = [description rangeOfString:@"?id="];
                NSString *path = [description substringWithRange: NSMakeRange(first.location + first.length, second.location - (first.location + first.length))];
                NSLog(@"Path: %@", path);

                NSNumber *width = [[[asset defaultRepresentation] metadata] objectForKey:@"PixelWidth"];
                NSString *widthString = [NSString stringWithFormat:@"%@", width];

                [myContainerArray addObject:widthString];
            }
        }];
    }
} failureBlock:^(NSError *error) {
    NSLog(@"error enumerating AssetLibrary groups %@\n", error);
}];

现在请记住，我已经为此示例创建了一个局部变量，您需要创建一个更大范围的变量才能在其他地方访问该数组。然后，您可以使用 [array objectAtIndex:i]; 或现代 Objective C 语法 array[i]; 通过索引访问数组的元素。