ios - NSString 类别中的扩展属性崩溃

Question

我刚刚在 Category 类中为 NSString 类创建了一个 Extension

#import "NSString+Name.h"

@interface NSString(Name)

@property (nonatomic, retain) NSString *var;

@end

但是当我尝试访问类别类中的私有(private)变量时，应用程序崩溃并给出错误。

@implementation NSString (Name)

- (NSString*)newString{

    [self setVar:@"Its a new string"];    // Crashes here

    NSLog(@"name = %@",self.var);

    return self.var;
}

@end

崩溃原因

unrecognized selector sent to instance 0x1023641c8 2015-05-25 11:12:49.246 Tute[710:14433] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFConstantString setVar:]: unrecognized selector sent to instance 0x1023641c8'

如果我能够在那个变量中赋值那么为什么它说无法识别的选择器

Answer 1

您应该使用关联对象。在下面找到对我有用的代码:

.h

@interface NSString (Name)

@property (nonatomic, assign)NSString *var;
- (NSString*)newString;
@end

.m

static char const * const Key = "SomeKey";

@implementation NSString (Name)

- (NSString*)newString
{
    self.var = @"Its a new string";
    NSLog(@"name = %@",self.var);

    return (self.var);
}

- (void)setVar:(NSString *)aVar {
    objc_setAssociatedObject(self, Key, aVar, OBJC_ASSOCIATION_ASSIGN);
}

- (NSString*)var {
    return (NSString*)objc_getAssociatedObject(self, Key);
}

引用here , here和 here