Objective-C消息传递，智能处理未知消息

发布于 2024-07-14 05:01:12 字数 1005 浏览 3 评论 0 原文

有没有办法做类似于 KVC 的事情，但使用消息名称作为密钥本身？例如，有没有一种方法可以让对象响应所有消息，而不是 valueForKey:？

例如，假设您有一个 XML 文档：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ...>
<employees>
  <employee>
    <name>Bill</name>
    <department>Accounting</department>
  </employee>
  <employee>
    <name>John</name>
    <department>Human Resources</department>
  </employee>
</employees>

除了使用已经可用的 NSXMLDocument 等之外，是否还有一种方法可以实现某种抽象，以便您可以这样做：

MyXML *xmlDoc = [[MyXML alloc] initWithContentsOfFile:@"test.xml"];

NSLog (@"%@", [[[xmlDoc employees] first] department]);

[[[xmlDoc employees] first] setDepartment:@"Management"];

我选择 XML 只是作为示例，但我想知道这是否可能，以及它是否涉及太接近 Objective-C 运行时，或者运行时本身是否支持它，以及我将如何实现这样的东西。这纯粹是为了实验目的，我知道这可能会产生巨大的性能成本。

编辑：
如果可能的话，我想避免使用 Cocoa 等现有框架，并使用基本 Objective-C 对象 Object。

原文

Is there a way to do something similar to KVC but use the message name as the key itself? For example, rather than valueForKey:, is there a way for an object to respond to all messages?

For example, say you have an XML document:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ...>
<employees>
  <employee>
    <name>Bill</name>
    <department>Accounting</department>
  </employee>
  <employee>
    <name>John</name>
    <department>Human Resources</department>
  </employee>
</employees>

Besides using the already-available NSXMLDocument and co., would there be a way to implement some sort of abstraction so you could do:

MyXML *xmlDoc = [[MyXML alloc] initWithContentsOfFile:@"test.xml"];

NSLog (@"%@", [[[xmlDoc employees] first] department]);

[[[xmlDoc employees] first] setDepartment:@"Management"];

I chose XML just as an example, but I want to know whether this is possible at all, and whether or not it involves getting too close to the Objective-C runtime or whether it is supported by the runtime itself, and how I would go about implementing something like this. This is purely for experimental purposes and I understand that there will likely be significant performance costs.

EDIT:
If possible, I'd like to avoid existing frameworks such as Cocoa and use the base Objective-C object Object.

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祁梦 2024-07-21 05:01:12

您需要实现 forwardInspiration: 和 methodSignatureForSelector: 来处理无法识别的消息。它是 NSObject 参考中进行了描述。

编辑：维基百科有一个示例基本上说明了如何为对象完成转发通过实现 forward: 和 performv:。

回复收藏 0 原文

鹤舞 2024-07-21 05:01:12

感谢 codelogic，我发现您需要为 GCC 的 Objective-C 运行时做的就是：

#import <obc/Object.h>
#import <stdio.h>

@interface RespondsToEverything : Object {}
@end

@implementation RespondsToEverything
- (retval_t) forward:(SEL) sel :(arglist_t) argFrame
{
    fprintf (stderr, "Received: %s\n", get_sel_name (sel));
}
@end

int main (int argc, char *argv[])
{
    id test = [RespondsToEverything new];
    [test asdfasdfasdfasdf];
    [test zxcvzxcvzxcvzxcv];

    return 0;
}

输出是：

Received: asdfasdfasdfasdf
Received: zxcvzxcvzxcvzxcv

但是当然，GCC 抱怨它找不到 asdfasdfasdfasdf 和 的方法签名>zxcvzxcvzxcvzxcv。没什么大不了的，它仍然表明这个概念是可行的。在 Apple 的运行时中，您可以使用 sel_getName(sel) 而不是 get_sel_name(sel)。

Thanks to codelogic, I've found out all you need to do for GCC's Objective-C runtime is:

#import <obc/Object.h>
#import <stdio.h>

@interface RespondsToEverything : Object {}
@end

@implementation RespondsToEverything
- (retval_t) forward:(SEL) sel :(arglist_t) argFrame
{
    fprintf (stderr, "Received: %s\n", get_sel_name (sel));
}
@end

int main (int argc, char *argv[])
{
    id test = [RespondsToEverything new];
    [test asdfasdfasdfasdf];
    [test zxcvzxcvzxcvzxcv];

    return 0;
}

The output is:

Received: asdfasdfasdfasdf
Received: zxcvzxcvzxcvzxcv

But of course, GCC complains that it cannot find method signatures for asdfasdfasdfasdf and zxcvzxcvzxcvzxcv. Not a big deal, it still shows that the concept is doable. In Apple's runtime you can use sel_getName(sel) instead of get_sel_name(sel).