为什么我的 Xcode 变得疯狂并且忘记了一些明确定义的类? [英] Why has my Xcode gone crazy and forgot some clearly defined classes?

问题描述

我在尝试构建时突然收到这些错误:

I'm suddenly getting these errors when I try to build:

它说 MenuViewController 是未知类型.但它在那里非常清楚，甚至是进口的.它在编译源中，我尝试了清理"、清理构建文件夹"、退出 Xcode、重新启动等.

It's saying MenuViewController is an unknown type. But it's very clearly there and even imported. It's in Compile Sources, and I tried a "Clean", "Clean Build Folder", quit Xcode, reboot, etc.

在这种情况下发生了什么?我也可以命令单击 import 语句的类名，它会跳转到文件.当它是第三个属性中的 FavoritesViewController 时，它也说未知类型 MenuViewController...

What is going on in this case? I can also command click the import statement's class name and it jumps to the file. It's also saying unknown type MenuViewController when it's a FavoritesViewController in the third property...

推荐答案

说明

我已经看到当 .h 文件之间存在循环引用时会发生这种情况.#import 可防止文件被包含两次，但这有时意味着类未在您期望的位置声明.这是发生的事情:

I've seen this happen when there are circular references between .h files. #import prevents the file from being included twice, but it sometimes means that classes aren't declared exactly where you expect. Here's what happens:

ClassA.m:

#import "ClassA.h"
...

ClassA.h

#import "ClassB.h"

@interface ClassA : ClassB
@end

ClassB.h

#import "ClassA.h"

@interface ClassB
@property (nonatomic) ClassA *classA;
@end

1. ClassA.m 导入 ClassA.h.
2. ClassA.h 在声明 ClassA 之前导入 ClassB.h.
3. ClassB.h 导入了 ClassA.h，但它已经被导入了，所以这被忽略了.
4. ClassB 尝试使用 ClassA，但尚未声明.

解决方案

我通常做的只是#import .h 文件中的基类，前向声明类接口所需的任何类型，其余的#import.m 文件中的 .h 文件:

What I usually do is to #import just the base class in the .h file, forward declare any types needed by the class interface, and #import the rest of the .h files in the .m file:

ClassA.m:

#import "ClassA.h"
#import "ClassB.h"
...

ClassA.h

#import "ClassB.h"

@interface ClassA : ClassB
@end

ClassB.h

@class ClassA;

@interface ClassB
@property (nonatomic) ClassA *classA;
@end

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