Objective-C中的类别不起作用 [英] Categories in Objective-C aren't working

问题描述

我正在开发一个需要部署到iOS 3.1.3的iOS应用程序。我需要扩展NSData类的一些功能，并在NSData + Base64中使用以下代码（截断以显示有趣的部分）：

I'm developing an iOS application that needs to deploy to iOS 3.1.3. I need to extend some of the functionality of the NSData class and am using the following code inside NSData+Base64 (truncated to show the interesting part):

[...]

@interface NSData (Base64)

+ (NSData *)dataFromBase64String:(NSString *)aString;
- (NSString *)base64EncodedString;

@end

NSData + Base64.m

NSData+Base64.m

@implementation NSData (Base64)

[...]

//
// base64EncodedString
//
// Creates an NSString object that contains the base 64 encoding of the
// receiver's data. Lines are broken at 64 characters long.
//
// returns an autoreleased NSString being the base 64 representation of the
//  receiver.
//
- (NSString *)base64EncodedString
{
    size_t outputLength;
    char *outputBuffer =
        NewBase64Encode([self bytes], [self length], true, &outputLength);

    NSString *result =
        [[[NSString alloc]
            initWithBytes:outputBuffer
            length:outputLength
            encoding:NSASCIIStringEncoding]
        autorelease];
    free(outputBuffer);
    return result;
}

@end

但是，当我尝试向此选择器发送消息时：

However, when I try to message this selector:

NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];
NSString *hash = [HMAC base64EncodedString];

我收到以下错误：

 -[NSConcreteData base64EncodedString]: unrecognized selector sent to instance 0x6146e70
2010-11-09 13:44:41.443 SpringboardApplication[21318:40b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSConcreteData base64EncodedString]: unrecognized selector sent to instance 0x6146e70'

I阅读了很多有关类别问题的iOS 3.1.x.我尝试添加标志 -all_load 和 -ObjC （单独和一起）无济于事。我真的很感激如何使这个选择器工作的方向。

I read a lot about iOS 3.1.x having problems with categories. I tried adding the flags -all_load and -ObjC (both separately and together) to no avail. I would really appreciate some direction of how to get this selector to work.

谢谢！

推荐答案

您的类别似乎没有被编译或链接到您正在使用它的同一目标。您应该确保NSData + Base64.m被标记为由使用它的同一目标编译，方法是获取两个文件的信息并比较它们分配给它们的目标。

It really seems like your category isn't being compiled or linked into the same target that you're using it from. You should make sure that NSData+Base64.m is marked to be compiled by the same target that it's being used from by getting info on the two files and comparing the targets they're assigned to.

您可以执行的测试是向NSData + Base64.m添加带有#error错误消息的行，这将导致构建在到达时失败文件。像这样：

A test you can perform is to add a line with an #error error message to NSData+Base64.m, which will cause the build to fail when it gets to that file. Like this:

#error We're now compiling NSData+Base64.m

然后查看哪个目标无法编译。

Then look and see which target fails to compile.

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