如何在保持成员之间的链接的同时访问 NSDictionary 的另一个成员中的成员
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【中文标题】如何在保持成员之间的链接的同时访问 NSDictionary 的另一个成员中的成员【英文标题】：How do I access a member inside another member of NSDictionary while keeping a link between members 【发布时间】：2014-03-30 22:14:11 【问题描述】：NSDictionary 让我很困惑。它有点像我收集的结构和数组的混合体。我正在阅读 ios 编程书，它让我们将 JSON 对象放入 NSDictionary。对于返回键“标题”的对象来说一切都很好，但对于upcoming 类，upcoming 中有变量。在我的脑海中，这就是 NSDictionary 的构建方式。
struct classes
NSString *title;
struct upcoming[]
NSString *end_date;
NSString *start_date;
NSString *instructor;
我一直在尝试使用以下变体在for 循环中检索start_date：
NSLog(@"%@", [course objectForKey:@"upcoming.start_date"]);
我这样做的目的是将title 的字符串附加在upcoming 类中具有值的start_date。比如……
NSString *value = course[@"title"];
if ([course objectForKey@"upcoming"] [value stringByAppendingString:
@" course[@"upcoming.start_date"];
NSLog(@"%@", value);
我该如何做到，如果upcoming 有一个或多个值，那么它将通过附加显示的字符串来显示这些 start_date 值，否则它不会做任何事情？显然@ 987654336@不是办法！而start_date 本身没有指向相关title 的链接。我需要将它们都链接起来以附加适当的字符串。
解决办法：
NSString *title = [course objectForKey:@"title"];
NSArray *upcomingCourses = [course objectForKey:@"upcoming"];
if (upcomingCourses.count > 0
NSString *showDate = [NSString stringWithFormat:@"%@. Next Class Date: %@"
title, [[upcomingCourses objectAtIndex:0] objectForKey:@"start_date"]];
NSLog(@"%@", showDate);
else NSLog(@"%@", title);
从NSLog发布NSDictionary：
courses = (
title = "Advanced iOS Bootcamp";
upcoming = (
"end_date" = "2014-04-04";
instructors = Blocksom;
location = "BNR West, California";
"start_date" = "2014-03-31";
,
"end_date" = "2014-05-16";
instructors = Dalrymple;
location = "BNR West, California";
"start_date" = "2014-05-12";
,
"end_date" = "2014-06-20";
instructors = Ward;
location = "Atlanta, Georgia";
"start_date" = "2014-06-16";
);
url = "https://training.bignerdranch.com/classes/advanced-ios-bootcamp";
,
title = "Beginning iOS (iPhone/iPad)";
upcoming = (
"end_date" = "2014-04-18";
instructors = Mathias;
location = "BNR West, California";
"start_date" = "2014-04-12";
,
"end_date" = "2014-05-02";
instructors = "Keur, Ward";
location = "Atlanta, Georgia";
"start_date" = "2014-04-26";
,
"end_date" = "2014-05-23";
instructors = Christopher;
location = "Atlanta, Georgia";
"start_date" = "2014-05-17";
,
"end_date" = "2014-06-06";
instructors = Christopher;
location = "BNR West, California";
"start_date" = "2014-05-31";
,
"end_date" = "2014-07-25";
instructors = Ritchie;
location = "BNR West, California";
"start_date" = "2014-07-19";
,
"end_date" = "2014-08-01";
instructors = "Usiyan, Keur";
location = "Atlanta, Georgia";
"start_date" = "2014-07-26";
,
"end_date" = "2014-09-19";
instructors = Ritchie;
location = "BNR West, California";
"start_date" = "2014-09-13";
);
url = "https://training.bignerdranch.com/classes/beginning-ios";
,
title = "Mobile Design Bootcamp";
upcoming = (
"end_date" = "2014-06-13";
instructors = "Harper, Porter";
location = "BNR West, California";
"start_date" = "2014-06-09";
);
url = "https://training.bignerdranch.com/classes/mobile-design-bootcamp";
,
title = "Python Programming";
upcoming = (
"end_date" = "2014-04-24";
instructors = Cassell;
location = "Atlanta, Georgia";
"start_date" = "2014-04-21";
,
"end_date" = "2014-06-19";
instructors = Cassell;
location = "BNR West, California";
"start_date" = "2014-06-16";
);
url = "https://training.bignerdranch.com/classes/python-programming";
,
title = "Beginning iOS Game Development";
upcoming = (
"end_date" = "2014-06-20";
instructors = Strougo;
location = "BNR West, California";
"start_date" = "2014-06-16";
,
"end_date" = "2014-09-26";
instructors = Strougo;
location = "BNR West, California";
"start_date" = "2014-09-22";
);
url = "https://training.bignerdranch.com/classes/beginning-ios-game-development";
,
title = "android Bootcamp";
upcoming = (
"end_date" = "2014-05-16";
instructors = Phillips;
location = "Atlanta, Georgia";
"start_date" = "2014-05-12";
,
"end_date" = "2014-06-20";
instructors = Marsicano;
location = "Atlanta, Georgia";
"start_date" = "2014-06-16";
,
"end_date" = "2014-07-11";
instructors = Stewart;
location = "BNR West, California";
"start_date" = "2014-07-07";
,
"end_date" = "2014-10-03";
instructors = Phillips;
location = "BNR West, California";
"start_date" = "2014-09-29";
);
url = "https://training.bignerdranch.com/classes/android-bootcamp";
,
title = "html5 Apps with jQuery";
upcoming = (
"end_date" = "2014-05-16";
instructors = Aquino;
location = "Atlanta, Georgia";
"start_date" = "2014-05-12";
,
"end_date" = "2014-06-13";
instructors = Gandee;
location = "Atlanta, Georgia";
"start_date" = "2014-06-09";
,
"end_date" = "2014-08-01";
instructors = Aquino;
location = "BNR West, California";
"start_date" = "2014-07-28";
);
url = "https://training.bignerdranch.com/classes/html5-apps-with-jquery";
,
title = "Ruby on the Server";
upcoming = (
"end_date" = "2014-06-13";
instructors = Stewart;
location = "Atlanta, Georgia";
"start_date" = "2014-06-09";
);
url = "https://training.bignerdranch.com/classes/ruby-on-the-server";
,
title = "iOS Bootcamp - Fast Track";
upcoming = (
"end_date" = "2014-07-11";
instructors = Usiyan;
location = "Atlanta, Georgia";
"start_date" = "2014-07-07";
);
url = "https://training.bignerdranch.com/classes/ios-bootcamp-fast-track";
,
title = "Cocoa I Bootcamp";
upcoming = (
"end_date" = "2014-07-25";
instructors = Preble;
location = "Atlanta, Georgia";
"start_date" = "2014-07-21";
);
url = "https://training.bignerdranch.com/classes/cocoa-i-bootcamp";
,
title = "OpenGL ES Bootcamp";
upcoming = (
"end_date" = "2014-07-25";
instructors = Blocksom;
location = "Atlanta, Georgia";
"start_date" = "2014-07-21";
);
url = "https://training.bignerdranch.com/classes/opengl-es-bootcamp";
);
【问题讨论】：
NSDictionary 是 set（不重复）键和值集合之间的映射。根据您熟悉的其他语言，您可能将其结构称为“associative array”、“哈希表”或“映射”。每个键对应一个值；它们是成对的，并且这些对是无序的。
你能把你的字典的实际构造或布局放入问题中吗？通过NSLog() 打印出来就可以了。
@JoshCaswell 已更新。好长啊！
在您做任何其他事情之前，请访问 json.org 并学习 JSON 语法。只需5-10分钟。虽然 Java 人喜欢通过将其直接映射到结构来使其过于复杂，但实际上，最好将其设想为数组和字典（哈希表）的“树”。 （如果你想用 Objective-C 去任何地方，你需要非常熟悉 NSArray 和 NSDictionary，因为它们处理应用程序中大约 80% 的数据。）
请注意，在上面的转储中，最外层的“层”（由() 字符括起来）是一个NSArray，下一层（由()），它又包含更多的字典。该方案的美妙之处在于，您可以仅使用这两个简单对象（NSArray 和 NSDictionary）来表示相对任意结构的数据结构。这也是 JSON 的美妙之处，因为它的“数组”和“对象”很好地映射到了 Objective-C 结构。
【参考方案1】：
NSDictionary 允许您通过键检索对象。键只是另一个对象，但通常使用 NSString（限制是键必须是唯一的，值不需要是唯一的）。任何对象都可以存储在键下，因此在您的情况下，“即将到来”是一个 NSDictionaries 数组。所以你得到了
dictionary
title: someString
upcoming: array
0: dictionary
end_date: somestring
start_date: someString
instructor: someString
1: dictionary
end_date: somestring
start_date: someString
instructor: someString
请注意，以上不是任何特定的语言或语法，只是数据“结构”的表示。
要检索课程详细信息，您可以像访问任何其他对象一样访问“即将到来的”对象并将其分配给一个变量。
假设course 是您的根NSDictionary：
NSString *title=(NSString *)[course objectForKey:@"title"];
NSArray *upcomingCourses=(NSArray *)[course objectForKey:@"upcoming"];
NSMutableString *startDates=[[NSMutablestring alloc]init];
for (int i=0;i<[upcomingCourses count];i++)
NSDictionary *upcomingCourse = (NSDictionary *)[upcomingCourses objectAtIndex:i];
NSString *startDate = (NSString *)[upcomingCourse objectForKey:@"start_date"];
NSString *endDate = (NSString *)[upcomingCourse objectForKey:@"end_date"];
NSString *instructor = (NSString *)[upcomingCourse objectForKey:@"instructor"];
[startDates appendFormat:@"%@, ",startDate];
【讨论】：
你能告诉我一些粗略的语法如何将它添加到for 循环中吗？也许我需要将对象添加到数组中以链接它们？
对不起，我错过了即将到来的是一个数组 - 让我修改我的答案
嗯，我想我需要回去重新学习 NSDictionary。我根本不处理这个。我仍然期待看到类似if (objectKey@"title" hasNonNullObject: objectKey@"upcoming") doSomething(); 的东西我无法想象这将如何连接字符串。
即将到来的总是有一个对象 - 一个数组 - 该数组可能有 0 个条目。我的答案中的 for 循环处理这种情况，因为 count 将为 0 并且 0 不
它显示了我希望它显示的内容，我仍在使用代码来理解它，但你给了我很大的推动力，朝着正确的方向发展。谢谢！以上是关于如何在保持成员之间的链接的同时访问 NSDictionary 的另一个成员中的成员的主要内容，如果未能解决你的问题，请参考以下文章
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