NSArray, NSDictionary支持下標(biāo)運(yùn)算符，使用下標(biāo)運(yùn)算符，可以使代碼看起來比較優(yōu)雅，工程師也可以少輸入很多字符。那么問題來了，能不能讓我們自定義的類也支持下標(biāo)運(yùn)算符呢？答案是“可以”，并且實(shí)現(xiàn)起來很簡(jiǎn)單。

如果想支持索引下標(biāo)，自定義的類需要實(shí)現(xiàn)如下兩個(gè)方法：

- (id)objectAtIndexedSubscript: (NSUInteger)idx;
- (void)setObject: (id)obj atIndexedSubscript: (NSUInteger)idx;

如果想支持鍵值下標(biāo)，自定義的類需要實(shí)現(xiàn)如下兩個(gè)方法：

- (id)objectForKeyedSubscript: (id<NSCopying>)key;
- (void)setObject: (id)obj forKeyedSubscript: (id<NSCopying>)key;

例子

頭文件

@interface TestSubscripting : NSObject

- (id)objectAtIndexedSubscript: (NSUInteger)idx;
- (void)setObject: (id)obj atIndexedSubscript: (NSUInteger)idx;

- (id)objectForKeyedSubscript: (id<NSCopying>)key;
- (void)setObject: (id)obj forKeyedSubscript: (id<NSCopying>)key;

@end

實(shí)現(xiàn)文件

@interface TestSubscripting ()

@property (nonatomic, strong) NSMutableArray *array;
@property (nonatomic, strong) NSMutableDictionary *dictionary;

@end

@implementation TestSubscripting

- (instancetype)init {
    self = [super init];
    if (self) {
        _array = [NSMutableArray array];
        _dictionary = [NSMutableDictionary dictionary];
    }
    
    return self;
}

- (id)objectAtIndexedSubscript:(NSUInteger)idx {
    return self.array[idx];
}

- (void)setObject:(id)obj atIndexedSubscript:(NSUInteger)idx {
    self.array[idx] = obj;
}

- (id)objectForKeyedSubscript:(id<NSCopying>)key {
    return self.dictionary[key];
}

- (void)setObject:(id)obj forKeyedSubscript:(id<NSCopying>)key {
    self.dictionary[key] = obj;
}
@end