objective-c - NSDictionary 中键的路径

Question

在我的应用程序中，我需要将值插入只有最后一个路径组件的 NSDictionary 中。例如。我给定的字典是

a = 1;
b = 2;
c = 3;
d =     {
    e = 4;
    f = 5;
    g =         {
        h = 6;
    };
};
j =     {
    k = 7;
};

我需要更改k的值。路径组件应为@[@"j", @"k"]。我尝试过类似的东西:

- (void)recurse:(NSDictionary*)dict keyToFound:(NSString*)ktf stack:(NSMutableArray*)stack parent:(NSString*)parent
{
    for (NSString *key in [dict allKeys]) {
    if ([key isEqualToString:ktf]) {
        [stack insertObject:key atIndex:[stack count]];

        return;
    }
    else {
        if ([[dict valueForKey:key] isKindOfClass:[NSDictionary class]]) {
            NSDictionary *d = [dict valueForKey:key];
            [stack insertObject:key atIndex:[stack count]];
            [self recurse:d keyToFound:ktf stack:stack parent:key];
            //[stack removeObject:key];
        }
    }
}

}

但是，显然，这是一种错误的方式。

Answer 1

这里有两种在嵌套字典中设置值的更简单的方法。第一个假设您知道键存在并且可能是 C 标识符。在这种情况下，使用 setValue:forKeyPath: 是最好的方法。否则，函数中的简单循环(或 NSDictionary 上的方法或类别)就可以解决问题:

void setValueForPathComponentsOfDictionary(id value, NSArray *components, NSMutableDictionary *dict) {

    NSMutableArray *parts = [components mutableCopy];
    id lastPart = parts.lastObject;
    [parts removeLastObject];

    for (id part in parts) {
        if (![dict respondsToSelector:@selector(objectForKey:)])
            return; // Silently fail.
        dict = [dict objectForKey:part];
    }

    if ([dict respondsToSelector:@selector(objectForKey:)])
        [dict setValue:value forKey:lastPart];
}

int main (int argc, const char * argv[])
{
    @autoreleasepool {

        NSMutableDictionary *dict = [@{
            @"a":[@{@"a":@1,@"b":@2} mutableCopy],
            @"b":[@{@"a":@3,@"b":@4} mutableCopy]
        } mutableCopy];

        NSLog(@"Initial Dictionary: %@", dict);

        [dict setValue:@9 forKeyPath:@"a.b"];
        NSLog(@"After setValue:forKeyPath: %@", dict);

        setValueForPathComponentsOfDictionary(@0, @[@"b",@"a"], dict);
        NSLog(@"After setValueForPathComponentsOfDictionary %@", dict);
    }
    return 0;
}