objective-c – 使用不同的子类属性创建子类

概述说我有这个班级 @interface CustomClass : NSObject@property (nonatomic, strong) NSArray * nicestArrayEver;@end 我想创建一个CustomClass的子类,但这里是catch @interface ASubClassCustomClass : CustomClass@property (nonat 说我有这个班级

@interface CustomClass : NSObject@property (nonatomic,strong) NSArray * nicestArrayEver;@end

我想创建一个CustomClass的子类,但这里是catch

@interface ASubClassCustomClass : CustomClass@property (nonatomic,strong) NSMutableArray * nicestArrayEver;@end

你可以想象的问题是,当我初始化ASubClassCustomClass并调用它的超级初始化器(因为还需要其他属性)时,会创建不可变的nicestArrayEver ..我怎样才能避免它的创建,所以我可以设置可变的？

注意：这只是一个例子,真正的实现调用了很多创建和真正定制的子类(不是NSArray).

解决方法 您可以通过使用不同的后备变量使其工作,在合成它时如下所示：@synthesize nicestArrayEver = nicestArrayEverSubClass_;

#import <Foundation/Foundation.h>@interface CustomClass : NSObject@property (nonatomic,strong) NSArray * nicestArrayEver;@end@implementation CustomClass@synthesize nicestArrayEver ;-(ID)init{    if (self = [super init]) {        nicestArrayEver = [[NSArray alloc] init];    }    return self;}@end@interface ASubClassCustomClass : CustomClass@property (nonatomic,strong) NSMutableArray * nicestArrayEver;@end@implementation ASubClassCustomClass@synthesize nicestArrayEver = nicestArrayEverSubClass_;-(ID)init{    if (self = [super init]) {        nicestArrayEverSubClass_ = [[NSMutableArray alloc] init];    }    return self;}@endint main(int argc,const char * argv[]){    @autoreleasepool {        CustomClass *c1 = [[[CustomClass alloc] init] autorelease];        ASubClassCustomClass *c2 = [[[ASubClassCustomClass alloc] init] autorelease];        NSLog(@"%@",NsstringFromClass([[c1 nicestArrayEver] class]));        NSLog(@"%@",NsstringFromClass([[c2 nicestArrayEver] class]));    }    return 0;}

产量

2012-05-27 01:59:16.221 NicestArray[2312:403] __NSArrayI2012-05-27 01:59:16.225 NicestArray[2312:403] __NSArrayM

另一种方法可能是在基类中有两个init方法,一个用于实例化属性,另一个用于子类的任务 – 这将阻止你创建昂贵的对象只是为了抛出它们远.@H_502_40@现在,基类可以直接使用第二个init进行实例化,并进入false状态.您可以通过使用isMemberOfClass：检查自类类型来避免这种情况,如果类类型是基类,则抛出错误.

@interface CustomClass : NSObject@property (nonatomic,strong) NSArray * nicestArrayEver;-(ID)initWithoutArray;@end@implementation CustomClass@synthesize nicestArrayEver ;-(ID) initWithoutArray{    if (self = [super init]) {        if ([self isMemberOfClass:[CustomClass class]]) {            [NSException raise:@"AbstractMethodCall" format:@"%@ should be called only from Subclasses of %@",NsstringFromSelector(_cmd),NsstringFromClass([self class])];        }    }    return self;}-(ID)init{    if (self = [super init]) {        nicestArrayEver = [[NSArray alloc] init];    }    return self;}@end@interface ASubClassCustomClass : CustomClass@property (nonatomic,strong) NSMutableArray * nicestArrayEver;@end@implementation ASubClassCustomClass@synthesize nicestArrayEver = nicestArrayEverSubClass_;-(ID)init{    if (self = [super initWithoutArray]) {        nicestArrayEverSubClass_ = [[NSMutableArray alloc] init];    }    return self;}@endint main(int argc,NsstringFromClass([[c2 nicestArrayEver] class]));        //this works,as it is the subclass        ASubClassCustomClass *shoulDWork = [[[ASubClassCustomClass alloc] init] autorelease];        // ouch!        CustomClass *shouldCrash = [[[CustomClass alloc] initWithoutArray] autorelease];    }    return 0;}

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