Objective-C使用#import和继承 [英] Objective-C use of #import and inheritance

问题描述

我有一个假设的UIViewController类名为foo。 foo继承自类别栏和类别bar＃import的A类，foo广泛使用的类。问题是，当我在foo中使用类A的实例时，我没有得到任何编译器错误，但我得到一个警告，例如，A类的实例不响应一个特定的方法。我必须显式#import ClassA.h到类'foo'？即使类foo扩展了扩展栏，它已经导入了它吗？

I have a hypothetical UIViewController class named "foo". foo inherits from class bar and class bar #import's "Class A", a class which foo uses extensively. The problem is, when I'm using an instance of class A in foo, I don't get any compiler errors, but I do get a warning for instance, that an instance of Class A does not respond to a particular method. Do I have to explicitly #import ClassA.h into class 'foo'? even though class foo extends extends bar, which already imports it?

希望这不是太混乱。让我知道如果我需要清除任何东西。

Hope that's not too confusing. Let me know if I need to clear anything up.

推荐答案

这听起来像你有一个循环依赖问题。为了解决它，是的，每个实现文件（ .m ）需要 #import 正确的头文件。但是，如果您尝试让头文件 #import 彼此，就会遇到问题。

It sounds like you have a circular dependency issue. In order to resolve it, yes, each imlementation file (.m) needs to #import the proper header file. However, if you try to have the header files #import each other, you'll run into problems.

为了使用继承，你需要知道超类的大小，这意味着你需要 #import 它。对于其他事情，虽然，例如作为指针的成员变量，或作为参数或返回其他类型的方法，你实际上不需要类定义，所以你可以使用前向引用解决编译器错误。

In order to use inheritance, you need to know the size of the superclass, which means you need to #import it. For other things, though, such as member variables which are pointers, or methods which take as a parameter or return the other type, you don't actually need the class definition, so you can use a forward reference to resolve the compiler errors.

// bar.h
@class A;  // forward declaration of class A -- do not to #import it here

@interface bar : UIViewController
{
    A *member;  // ok
}

- (A) method:(A)parameter;  // also ok
@end

// bar.m
#import "bar.h"
#import "A.h"

// can now use bar & A without any errors or warnings

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