有没有办法在 Objective-C 中添加不在头文件中的 iVar（不使用 LLVM 2.0 或更高版本）？

发布于 2024-11-01 08:18:57 字数 347 浏览 8 评论 0原文

我最近了解到可以使用 LLVM2.0 在类扩展中添加 ivar。（海湾合作委员会不能这样做）这在某种程度上是真正私有的 iVar，因为其他用户不知道它的存在，因为它不在头文件中。 like：

//SomeClass.h
@interface SomeClass : NSObject {

}
@end

//SomeClass.m
@interface SomeClass ()
{
    NSString *reallyPrivateString;
}
@end

@implementation SomeClass

@end

但这确实依赖于编译器。还有其他方法可以声明头文件中没有的 ivar 吗？

原文

I recently learned that you can add ivar in a class extension with LLVM2.0. (gcc can't do this)
This is somehow really private iVar because other users don't it's existence since it's not in the header file.
like:

//SomeClass.h
@interface SomeClass : NSObject {

}
@end

//SomeClass.m
@interface SomeClass ()
{
    NSString *reallyPrivateString;
}
@end

@implementation SomeClass

@end

But this does rely on the compiler. Is there any other way to declare an ivar that's not in the header file?

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海未深 2024-11-08 08:18:57

声明实例变量的唯一位置是接口或类扩展（实际上是接口的扩展）。但是您可以使用关联对象函数。

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千柳 2024-11-08 08:18:57

如果您正在实现一个库并想要隐藏实例变量，请查看 Apple 在 UIWebView 界面中所做的操作。它们有一个不公开头文件的内部 Web 视图。

@class UIWebViewInternal;
@protocol UIWebViewDelegate;

UIKIT_CLASS_AVAILABLE(2_0) @interface UIWebView : UIView <NSCoding, UIScrollViewDelegate> { 
 @private
    UIWebViewInternal *_internal;
}

If you are implementing a library and want to hide your instance variables take a look at what Apple does in the interface for UIWebView. They have an internal webview that does not expose a header file.

@class UIWebViewInternal;
@protocol UIWebViewDelegate;

UIKIT_CLASS_AVAILABLE(2_0) @interface UIWebView : UIView <NSCoding, UIScrollViewDelegate> { 
 @private
    UIWebViewInternal *_internal;
}

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我纯我任性 2024-11-08 08:18:57

如果您只是要在内部使用 ivar，并且您使用的是现代运行时（我认为是 Snow Leopard 64 位和 iOS 3.0+），那么您可以在类扩展中声明属性并在类中合成它们。您的标头中没有暴露 ivars，没有混乱的 id _internal 对象，并且您也可以绕过脆弱的 ivars。

// public header
@interface MyClass : NSObject {
// no ivars
}
- (void)someMethod;
@end

// MyClass.m
@interface MyClass ()
@property (nonatomic, retain) NSString *privateString;
@end

@implementation MyClass
@synthesize privateString;

- (void)someMethod { 
    self.privateString = @"Hello";
    NSLog(@"self.privateString = %@", self.privateString);
    NSLog(@"privateString (direct variable access) = %@", privateString); // The compiler has synthesized not only the property methods, but also actually created this ivar for you. If you wanted to change the name of the ivar, do @synthesize privateString = m_privateString; or whatever your naming convention is
}
@end

除了 LLVM 之外，它还可以与 Apple 的 gcc 一起使用。（我不确定这是否适用于其他平台，即不适用于 Apple 的 gcc，但它肯定适用于 iOS 和 Snow Leopard+）。

If you're just going to be using the ivar internally, and you're using the modern runtime (Snow Leopard 64 bit and iOS 3.0+, I think) then you can just declare properties in a class extension and synthesize them inside the class. No ivars are exposed in your header, no messy id _internal objects, and you get around fragile ivars, too.

// public header
@interface MyClass : NSObject {
// no ivars
}
- (void)someMethod;
@end

// MyClass.m
@interface MyClass ()
@property (nonatomic, retain) NSString *privateString;
@end

@implementation MyClass
@synthesize privateString;

- (void)someMethod { 
    self.privateString = @"Hello";
    NSLog(@"self.privateString = %@", self.privateString);
    NSLog(@"privateString (direct variable access) = %@", privateString); // The compiler has synthesized not only the property methods, but also actually created this ivar for you. If you wanted to change the name of the ivar, do @synthesize privateString = m_privateString; or whatever your naming convention is
}
@end

This works with Apple's gcc, in addition to LLVM. (I'm not sure if this works on other platforms, ie not Apple's gcc, but it will certainly work for both iOS and Snow Leopard+).

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