键值编码及其脚本能力

发布于 2024-07-10 05:38:15 字数 597 浏览 6 评论 0原文

我有一个直接实例变量的对象。有些是 NSString，有些是无符号整数，等等。我的印象是键值编码是可脚本化的，因为我可以编写如下代码：

   id key, value;
   key      = [[attributes objectAtIndex:j] name];
   value    = [[attributes objectAtIndex:j] stringValue];
   [obj setValue:value forKey:key];

我在这里使用 stringValue 和 name 的原因是我正在使用 TouchXML以及从 XML feed 构建对象。

如果我尝试将任何内容分配给整数，上面的代码就会崩溃。如果我将 unsigned int 更改为 NSString 的实例，则不会出现任何运行时崩溃。据我了解，键值编码足够智能来检测这些问题。

我可能的解决方案是什么？我如何尽可能地抽象它，以便我可以在许多不同的类上运行相同的方法，这些类都有自己的实例变量？

真正重写我的 setter 并使用 NSNumber 将字符串转换为 int 类型（我认为已经由 KVC 处理）的最优雅的方法是吗？

原文

I have an object which straight forward instance variables. Some are NSString, some are unsigned ints, etc. I was under the impression Key-Value coding was scriptable in that I could write code such as the following:

   id key, value;
   key      = [[attributes objectAtIndex:j] name];
   value    = [[attributes objectAtIndex:j] stringValue];
   [obj setValue:value forKey:key];

The reason I'm using stringValue here and name is I'm working with TouchXML and building objects from XML feeds.

The code above crashes if I try to assign anything to an integer. If I change my unsigned int to an instance of NSString, there isn't any run-time crashes. It was to my understanding that Key-Value coding is smart enough to detect these issue.

What are my possible solutions? How can I abstract this as much as possible so I can run the same method on many different classes which all have their own instance variables?

Is the most elegant method to really override my setter and use NSNumber to convert the string into a type int, which I thought was already handled by KVC?

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折戟 2024-07-17 05:38:15

KVC 不会在内部进行任何类型强制/转换，因此您传递给 setValue:forKey: 的对象类型必须与其将存储在其中的实例变量的类型相匹配。本机类型，例如int、long 等被打包成 NSNumber 对象，结构体之类的东西被打包成 NSValue 对象。要设置声明为本机类型的值，您应该为值参数传递适当的包装对象。

我还建议在调用 setter 的代码中进行任何所需的翻译，而不是在 setter 本身中。但这更多是一个意见问题，所以我想如果你真的愿意的话，你可以在设置器中翻译内容。我的代码版本看起来像这样：

id key, value;
key = [[attributes objectAtIndex:j] name];
value = [NSNumber numberWithInt:[[[attributes objectAtIndex:j] stringValue] intValue]];
[obj setValue:value forKey:key];

KVC doesn't do any type coercion/translation internally, so the type of the object you pass into setValue:forKey: must match the type of the instance variable it will be stored in. Native types such as int, long, etc. are packaged up into NSNumber objects, and things like structs get packed into NSValue objects. To set a value that's declared as a native type, you should pass an appropriate wrapper object in for the value argument.

I would also recommend doing any required translation in the code that's calling the setter, and not in the setter itself. That's more a matter of opinion though, so I suppose you could translate stuff in the setter if you really want to. My version of your code would look something like:

id key, value;
key = [[attributes objectAtIndex:j] name];
value = [NSNumber numberWithInt:[[[attributes objectAtIndex:j] stringValue] intValue]];
[obj setValue:value forKey:key];

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