错误:'NSObject'没有可见的@interface声明选择器'copyWithZone:'

Question

我想允许我的类对象的深层副本,并尝试实现copyWithZone,但调用[super copyWithZone:zone]产生错误:

error: no visible @interface for 'NSObject' declares the selector 'copyWithZone:'

@interface MyCustomClass : NSObject

@end

@implementation MyCustomClass

- (id)copyWithZone:(NSZone *)zone
{
    // The following produces an error
    MyCustomClass *result = [super copyWithZone:zone];

    // copying data
    return result;
}
@end

我该如何创建这个类的深层副本？

Answer 1

你应该添加 NSCopying协议到类的接口.

@interface MyCustomClass : NSObject <NSCopying>

那么方法应该是:

- (id)copyWithZone:(NSZone *)zone {
    MyCustomClass *result = [[[self class] allocWithZone:zone] init];

    // If your class has any properties then do
    result.someProperty = self.someProperty;

    return result;
}

NSObject不符合NSCopying协议.这就是你无法打电话的原因super copyWithZone:.

编辑:根据Roger的评论,我更新了copyWithZone:方法中的第一行代码.但根据其他评论,可以安全地忽略该区域.