Question

我对cocoa和Xcode很新，我已经完成了一些基本的C编码，但我非常厌恶Objective-c和cocoa，所以请原谅我犯下的任何愚蠢错误。我的问题是我正在使用的这些全局变量。我在头文件中声明了一个全局NSString变量，它在主文件中使用如下：

//AppController.h
-(IBAction)button1:(id)sender;
-(IBAction)button2:(id)sender;
extern NSString *hi
//AppController.m
-(IBAction)button1:(id)sender
{
NSString *const hi = @"Hello";
}
-(IBAction)button2:(id)sender;
{
NSLog (@"%@", hi);
}

但是，当我单击运行时，构建失败并收到错误消息：

“_ hi”，引自：

一些额外信息：

Undefined symbols for architecture x86_64: "_hi", referenced from: -[AppController gallery:] in AppController.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

如果你知道这意味着什么和/或如何解决它，请帮助我。感谢

Answer 1

您需要为hi提供全局定义。移动您的声明：

NSString *const hi = @"Hello";

到任何方法的外的某个地方。我不确定你想要button1:做什么，但对你的实现来说似乎没有必要。

Answer 2

我认为卢克喜欢：
单击按钮一后，将字符串设置为特定值，
并在单击按钮2后再次检索它。

<强> AppController.h

#import <Cocoa/Cocoa.h>

@interface AppController : NSObject{

    NSString * string;

}

-(IBAction)button1:(id)sender;
-(IBAction)button2:(id)sender;

@end

<强> AppController.m

#import "AppController.h"

@implementation AppController

-(IBAction)button1:(id)sender
{
    string = @"Hello";
}

-(IBAction)button2:(id)sender;
{
    NSLog (@"%@", string);
}

@end

Answer 3

在定义全局变量和常量字符串等时，通常我会这样做：

MDAppController.h：

#import <Cocoa/Cocoa.h>

extern NSString * const MDShouldShowInspectorKey;
extern NSString * const MDShouldShowViewOptionsKey;
extern BOOL MDShouldShowInspector;
extern BOOL MDShouldShowViewOptions;

@interface MDAppController : NSObject <NSApplicationDelegate> {
   IBOutlet NSWindow *window;
}
- (IBAction)hideInspector:(id)sender;
@end

MDAppController.m：

#import "MDAppController.h"
NSString * const MDShouldShowInspectorKey   = @"MDShouldShowInspector";
NSString * const MDShouldShowViewOptionsKey = @"MDShouldShowViewOptions";
BOOL MDShouldShowInspector = NO; // default value
BOOL MDShouldShowViewOptions = YES;  // default value

@implementation MDAppController
+ (void)initialize {
    NSMutableDictionary *defaultValues = [NSMutableDictionary dictionary];
    [defaultValues setObject:
        [NSNumber numberWithBool:MDShouldShowInspector]
                      forKey:MDShouldShowInspectorKey];

    [defaultValues setObject:
         [NSNumber numberWithBool:MDShouldShowViewOptions] 
                      forKey:MDShouldShowViewOptionsKey];

    [[NSUserDefaults standardUserDefaults] registerDefaults:defaultValues];
}
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSUserDefaults *uD = [NSUserDefaults standardUserDefaults];
    MDShouldShowInspector = [[uD objectForKey:MDShouldShowInspectorKey] boolValue];
    MDShouldShowViewOptions = [[uD objectForKey:MDShouldShowViewOptionsKey] boolValue];
}
- (IBAction)hideInspector:(id)sender {
    NSLog(@"MDShouldShowViewOptionsKey == %@", MDShouldShowViewOptionsKey);
    MDShouldShowInspector = NO;
    [[NSUserDefaults standardUserDefaults]
               setObject:[NSNumber numberWithBool:MDShouldShowInspector]
                    forKey:MDShouldShowInspectorKey];
}
@end

Answer 4

我的问题是你为什么要成为外界？这里最好的方法是创建一个单例，你应该把所有成员作为一个类的一部分，并避免任何全局。希望这有帮助

XCode中的全局字符串问题

4 个答案: