Question

我有一个单一类KTTTeacherService，它有一个属性currentTeacher。该属性最初为nil，并使用静态方法KTTTeacherService#updateCurrentTeacher进行更新。更新currentTeacher后，当我尝试访问它时，我的应用程序因EXC_BAD_ACCESS错误而崩溃。

KTTTeacherService.h

#import <Foundation/Foundation.h>
#import "KTTeacher.h"

@interface KTTTeacherService : NSObject
@property (nonatomic, assign) KTTeacher* currentTeacher;

+ (KTTTeacherService*)shared;
+ (KTTeacher*)currentTeacher;
+ (NSString*)apiKey;
+ (void)updateCurrentTeacher:(KTTeacher*) teacher;
- (KTTeacher*)retrieveCurrentTeacher;

@end

KTTTeacherService.m

#import "KTTTeacherService.h"
#import "KTTeacher.h"

static KTTTeacherService* _singleton = nil;

@implementation KTTTeacherService;

+ (KTTTeacherService*) shared {
  if(_singleton == nil) {
    _singleton = [[KTTTeacherService alloc] init];
  }
  return _singleton;
}

+ (KTTeacher*) currentTeacher {
  KTTTeacherService* shared = [KTTTeacherService shared];
  if(shared == nil) {
    return nil;
  }
  return [shared retrieveCurrentTeacher];
}

+ (NSString*) apiKey {
  KTTeacher* teacher = [KTTTeacherService currentTeacher];
  return teacher == nil ? nil : teacher.apiKey;
}

+ (void) updateCurrentTeacher:(KTTeacher*) teacher {
  [KTTTeacherService shared].currentTeacher = teacher;
}

- (KTTeacher*) retrieveCurrentTeacher {
  return _currentTeacher;
}

@end

KTTeacher.h

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@class KTClass, KTGroup, KTTeacherNote;

@interface KTTeacher : NSManagedObject

@property (nonatomic, strong) NSString * apiKey;
@property (nonatomic, strong) NSNumber * serverIdentifier;
@property (nonatomic, strong) NSString * firstName;
@property (nonatomic, strong) NSString * lastName;
@property (nonatomic, strong) NSString * photoPathOnServer;
@property (nonatomic, strong) NSString * username;
@property (nonatomic, strong) NSString * hashedPassword;
@property (nonatomic, strong) NSString * salt;
@property (nonatomic, strong) NSSet *classes;
@property (nonatomic, strong) NSSet *groups;
@property (nonatomic, strong) NSSet *notes;
@end

@interface KTTeacher (CoreDataGeneratedAccessors)

- (void)addClassesObject:(KTClass *)value;
- (void)removeClassesObject:(KTClass *)value;
- (void)addClasses:(NSSet *)values;
- (void)removeClasses:(NSSet *)values;

- (void)addNotesObject:(KTTeacherNote *)value;
- (void)removeNotesObject:(KTTeacherNote *)value;
- (void)addNotes:(NSSet *)values;
- (void)removeNotes:(NSSet *)values;

- (void)addGroupsObject:(KTGroup *)value;
- (void)removeGroupsObject:(KTGroup *)value;
- (void)addGroups:(NSSet *)values;
- (void)removeGroups:(NSSet *)values;

@end

KTTeacher.m

#import "KTTeacher.h"
#import "KTClass.h"
#import "KTTeacherNote.h"

@implementation KTTeacher

@dynamic apiKey;
@dynamic serverIdentifier;
@dynamic firstName;
@dynamic lastName;
@dynamic photoPathOnServer;
@dynamic username;
@dynamic hashedPassword;
@dynamic salt;
@dynamic classes;
@dynamic groups;
@dynamic notes;

@end

发生崩溃的地方：

KTTTeacherService* teacherService = [KTTTeacherService shared];

KTTeacher* currentTeacher = teacherService.currentTeacher;

具体来说：teacherService.currentTeacher

为什么会这样？在做了一些谷歌搜索之后，我发现了一些关于这个错误的信息是由访问垃圾收集的引用引起的，但我不明白为什么这个变量会被垃圾收集，因为单例保留了一个引用。

Answer 1

属性写错了。使用强，弱，保留而不是分配

属性（非原子，赋值）KTTeacher * currentTeacher;

Answer 2

我试图重现错误而我不能。创建一个项目并放置类KTTTeacherService，KTTeacher（带有apiKey属性的空类）一切正常。 因此，您必须在KTTeacher类中出现错误。

在viewDidLoad中，我有以下内容：

{{1}}

当你调用currentTeacher方法时，_currentTeacher（property）现在有一个值。

Objective-C访问singleton的属性导致EXC_BAD_ACCESS崩溃

2 个答案: