“未声明的变量"编译到 iOS 设备时出错，但不适用于模拟器

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问题描述

我有一个自定义 UIVIewController，它是其他控制器的基类，并且有一个自定义 UIView 变量的实例，该变量由继承的类访问.

I have an custom UIVIewController that is the base class for other controllers and has an instance of a custom UIView variable that is accessed by inherited the classes.

BaseViewController.h

@interface BaseViewController : UIViewController {
    UIView *_vwHeader;
}

@end

BaseViewController.m

#import "BaseViewController.h"
@implementation BaseViewController

-(void)loadView {

    [super loadView];

    _vwHeader = [[UIView alloc] init];
}

@end

CustomViewController.h

#import "BaseViewController.h"
@interface CustomViewController : BaseViewController

@end

CustomViewController.m

#import "CustomViewController.h"
@implementation CustomViewController

- (void)loadView
{
    [super loadView];

    [_vwHeader setHidden:NO];
}

@end

问题是，当我在模拟器上运行它时，一切正常，但是当我切换到设备时，我在 [_vwHeader setHidden:NO]; 行出现错误: '_vwHeader' 未声明(此函数中首次使用)

The problem is that when I am running it on the simulator everything works perfectly fine, but when I change to the device I have an error on the [_vwHeader setHidden:NO]; line which says: '_vwHeader' undeclared (first use in this function)

我已经尝试过:

注释这行代码，但是它在另一个类中以相同的方式使用基类中的变量给我一个错误(它一次只返回一个错误)，所以它似乎不是一个特定的错误在视图或控制器类中，因为错误发生在具有不同类型的其他类中，例如 UIView 和 NSObject 类型
更改目标编译器配置，例如:架构(所有这些)、基础 sdk(4.0 以上)没有改变任何东西

什么似乎解决了问题，但不完全

What seem to solve the problem, but not completely

为 _vwHeader 创建一个属性并通过 self._vwHeader 或 super._vwHeader 访问它似乎可行，但必须创建一个属性仅仅访问一个变量并不会让我感到舒服，特别是因为我必须在我的项目中为相同情况下的所有变量都这样做.
更改了 C/C++ 编译器版本:使用 Apple LLVM Compiler 2.1 使编译错误消失，但在项目中使用其他库时会出现一系列其他问题.因此，这不是最终的解决方案，但可能是问题所在的线索.

Creating a property for _vwHeader and accessing it by self._vwHeader or super._vwHeader seems to work, but having to create a property just to access a variable does not make me confortable, specially because I would have to do it for all variables in the same situation inside my project.
changed C/C++ compiler version: using Apple LLVM Compiler 2.1 makes the compilation error goes away, but gives a bunch of other problems with other libraries being used in the project. So, it is not a definitive solution, but might be a clue of what the problem is.

我试图创建另一个不是指针的变量，一个BOOL而不是UIView *然后在继承的类中使用它:问题也出现

I tried to create another variable that is not a pointer, a BOOL instead of the UIView * and then used it in the inherited class: the problem also occurs

编辑(2):

我的任何类中都没有任何属性，但仍然出现错误.我刚刚添加了测试海豚的属性，以查看父类中的属性是否导致了相同的行为，但显然没有.还有一点很奇怪，当我在变量中得到错误时，我检查了我的智能感知并找到了它......

I have no properties whatsoever in any of my classes and I still get the error.I just added the properties for test porpouses, to see if a property in a parent class caused the same behaviour, and apparently it doesn't.Something that is also weird is that when I get the error in the variable, I checked with my intellisense and it finds it...

推荐答案

为了在任何对象中引用一个实例变量而不是 self，包括 super，你必须使用结构指针运算符 (->).实例变量的默认范围是受保护的，这意味着它只能在定义它的类或该类的子类中访问.由于 CustomViewController 是 BaseViewController 的子类，所以这个范围足以使用 self->_vwHeader 访问变量，但是如果第二个类你试图从不是子类执行此操作，您还需要将范围更改为 @public 或 @package.

In order to refer to an instance variable within any object other than self, including super, you must use the structure pointer operator (->). The default scope of an instance variable is protected, which means it can only be accessed within the class it is defined in or a subclass of that class. Since CustomViewController is a subclass of BaseViewController, this scope is sufficient to access the variable using self->_vwHeader, but if the second class you were trying to do this from is not a subclass you will also need to change the scope to either @public or @package.

总而言之，将您的方法调用更改为:

In summary, change your method call to:

[self->_vwHeader setHidden:NO];

它应该适用于基本视图控制器的任何子类.

and it should work for any subclasses of the base view controller.

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