ios - 子类中的 Objective-C 只读属性

Question

我有一个名为 SuperClass 的父类(super class)，它是一个只读属性。看起来像这样:

@property (nonatomic, strong, readonly) NSArray *arrayProperty;

在一个子类中，我需要一个将 SuperClass 的实例作为参数的初始化器:

- (instancetype)initWithSuperClass:(SuperClass *)superClass

我创建了一个显示问题所在的 GitHub 示例项目:https://github.com/marosoaie/Objc-test-project

我不能在初始化程序中执行 _arrayProperty = superClass.arrayProperty。我也想在 SubClass 中将属性保持为只读。

关于如何解决这个问题有什么想法吗？

我知道我可以在 SubClass 实现文件中的类扩展中将该属性声明为读写，但我希望有比这更好的解决方案。

编辑:父类(super class).h

#import <Foundation/Foundation.h>

@interface SuperClass : NSObject
- (instancetype)initWithDictionary:(NSDictionary *)dictionary;

@property (nonatomic, strong, readonly) NSString *stringProperty;
@property (nonatomic, strong, readonly) NSArray *arrayProperty;

@end

父类(super class).m

#import "SuperClass.h"

@implementation SuperClass

- (instancetype)initWithDictionary:(NSDictionary *)dictionary
{
    self = [super init];
    if (self) {
        _arrayProperty = dictionary[@"array"];
        _stringProperty = dictionary[@"string"];
    }
    return self;
}

@end

子类.h:

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

@interface SubClass : SuperClass

@property (nonatomic, strong, readonly) NSString *additionalStringProperty;
- (instancetype)initWithSuperClass:(SuperClass *)superClass;

@end

子类.m:

#import "SubClass.h"

@implementation SubClass
@synthesize additionalStringProperty = _additionalStringProperty;

- (NSString *)additionalStringProperty
{
    if (!_additionalStringProperty) {
        NSMutableString *mutableString = [[NSMutableString alloc] init];

        for (NSString *string in self.arrayProperty) {
            [mutableString appendString:string];
        }

        _additionalStringProperty = [mutableString copy];
    }
    return _additionalStringProperty;
}

- (instancetype)initWithSuperClass:(SuperClass *)superClass
{
    self = [super init];
    if (self) {
//        Doesn't work
//        _stringProperty = superClass.stringProperty;
//        _arrayProperty = superClass.arrayProperty;

    }
    return self;
}



@end

Answer 1

您已经公开了一个初始化器，它写入只读属性 -initWithDictionary:。在您的子类中调用它，而不是 [super init]:

- (instancetype)initWithSuperClass:(SuperClass *)superClass {
    NSDictionary *dict = @{
        @"array": superClass.arrayProperty,
        @"string": superClass.stringProperty,
    };
    self = [super initWithDictionary:dict];
    if (self) {
        // Nothing here.
    }
    return self;
}

为只读属性设置初始化器是很常见的，尽管使用字典并不是很好的解决方案。通常，我会创建:

- (instancetype)initWithArray:(NSArray *)array string:(NSString *)string;