我已阅读 属性重新声明章节rel="nofollow">The Objective-C 编程语言 文档，我希望你们中的一些人可以向我澄清以下属性重新声明：
// MyObject.h public header file
@interface MyObject : NSObject {
NSString *language;
}
@property (readonly, copy) NSString *language;
@end
// MyObject.m private implementation file
@interface MyObject ()
@property (readwrite, copy) NSString *language;
@end
@implementation MyObject
@synthesize language;
@end
我只是想了解上面是否@property 和 @synthesize 关键字生成以下代码：
// MyObject.h public header file
@interface MyObject : NSObject {
NSString *language;
}
-(NSString *)language;
@end
// MyObject.m private implementation file
@interface MyObject ()
-(void)setLanguage: (NSString *) aString;
@end
@implementation MyObject
-(NSString *)language {
return language;
}
-(void)setLanguage: (NSString *) aString {
[language release];
language = [aString copy];
}
@end
因此，编译器会看到第一个 @property 声明并添加一个 getter公共接口中的方法...然后，当涉及到实现文件时，它会找到同一属性的另一个 @property 声明，但在私有接口中具有 readwrite 属性，并且仅添加一个 setter 方法，因为getter 已经添加到 public 中接口..然后，找到@synthesize关键字，并将两个实现都添加到私有实现部分..第一个@property声明的复制属性将不是必需的，因为那里不需要 setter，但我们必须指定它以与第二个属性重新声明一致。我的想法对吗？
I've read the Property redeclaration chapter in The Objective-C Programming Language document and I'd like if some of you can clarify me the following property redeclaration:
// MyObject.h public header file
@interface MyObject : NSObject {
NSString *language;
}
@property (readonly, copy) NSString *language;
@end
// MyObject.m private implementation file
@interface MyObject ()
@property (readwrite, copy) NSString *language;
@end
@implementation MyObject
@synthesize language;
@end
I just want to understand if the above @property and @synthesize keywords produce the following code:
// MyObject.h public header file
@interface MyObject : NSObject {
NSString *language;
}
-(NSString *)language;
@end
// MyObject.m private implementation file
@interface MyObject ()
-(void)setLanguage: (NSString *) aString;
@end
@implementation MyObject
-(NSString *)language {
return language;
}
-(void)setLanguage: (NSString *) aString {
[language release];
language = [aString copy];
}
@end
So, what happens is that the compiler sees the first @property declaration and adds a getter method in the public interface... than, when it comes to the implementation file it finds another @property declaration for the same property but with readwrite attribute within the private interface and adds only a setter method since the getter has been already added to the public interface.. then, the @synthesize keyword is found and both implementations are added to the private implementation section.. the copy attribute of the first @property declaration would not be necessary, since the setter is not needed there, but we must specify it to be consistent with the second property redeclaration. Are my thoughts right?
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评论（1）
是的，你的理解是正确的。
另请注意，Objective-C 中没有严格私有的方法。外部调用者仍然可以调用
setLanguage:。编译器将输出警告，但该消息将在运行时传递。Yes, your understanding is correct.
Also note that there are no strictly private methods in Objective-C. An external caller can still call
setLanguage:. The compiler will output a warning but the message would get through at runtime.