将一个模型数组的某个属性抽取为一个数组

一般

    NSMutableArray * mutableArray = [[NSMutableArray alloc] init];
    [array enumerateObjectsUsingBlock:^(Person * person, NSUInteger idx, BOOL * _Nonnull stop) {
        
        [mutableArray addObject:person.name];
    }];

但是每次都要遍历数组感觉挺麻烦的,就搜索了一下，发现其实是有现成的API的.
一句话就搞定了.不过注意不要把key写错了。

    NSArray * newArray = [array valueForKey:@"name"];

查看文档的注释:
/* Return an array containing the results of invoking -valueForKey: on each of the receiver's elements. ``The returned array will contain NSNull elements for each instance of -valueForKey: returning nil.
*/
- (id)valueForKey:(NSString *)key;