objective-c - Xcode:为什么我不能在一个项目中有重复的 ivars？出现重复符号错误

Question

我以前从未在 Xcode 中注意到这一点，但是当我尝试重用同名 ivar 时出现此错误。我用 2 个 ViewController 创建了一个简单的项目，它们都有 ivar 名称。

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

NSString *name;

- (void)viewDidLoad {
    [super viewDidLoad];

    name = @"me";

    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

#import "ViewController2.h"

@interface ViewController2 ()

@end

@implementation ViewController2

NSString *name;

- (void)viewDidLoad {
    [super viewDidLoad];

    name = @"Me";

    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

@end

当我运行这个项目时，我得到了这个错误:

duplicate symbol _name in:
    /Users/cta/Library/Developer/Xcode/DerivedData/testDuplicate2-cxeetzeptbwtewfecgmoonzgzeyl/Build/Intermediates/testDuplicate2.build/Debug-iphoneos/testDuplicate2.build/Objects-normal/arm64/ViewController.o
    /Users/cta/Library/Developer/Xcode/DerivedData/testDuplicate2-cxeetzeptbwtewfecgmoonzgzeyl/Build/Intermediates/testDuplicate2.build/Debug-iphoneos/testDuplicate2.build/Objects-normal/arm64/ViewController2.o
ld: 1 duplicate symbol for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

在你的实现中 name 不是一个实例变量，它是一个全局变量。事实上，您将它的声明放在 @implementation block 中并不能使它成为一个实例变量。

如果你想使 name 成为一个实例变量，将其声明为你的类扩展的一部分，如下所示:

@interface ViewController2 () {
    NSString *name;
}
@end

请注意，如果您需要 name 为 static，您的方法会奏效，因为 static 变量在衬里中是“隐藏”的.