给你一个嵌套的 NSArray 数据，实现一个迭代器类，该类提供一个 next() 方法，可以依次的取出这个 NSArray 中的数据。

ArrayIterator.h

#import <Foundation/Foundation.h>

@interface ArrayIterator : NSObject
@property (nonatomic, strong) NSArray *array;
- (id) next;
- (NSArray *) allObjects;
@end

ArrayIterator.m

#import "ArrayIterator.h"

@interface ArrayIterator ()
@property (nonatomic, strong) NSMutableArray<NSNumber *> *status;
@end

@implementation ArrayIterator
- (void) setArray:(NSArray *)array
{
    if (_array == array)
    {
        return;
    }
    
    _array = array;
    _status = @[@(-1)].mutableCopy;
}

- (NSArray *) currentArray
{
    if (_status.count < 2)
    {
        return _array;
    }
    
    NSArray *res = _array;
    for (NSUInteger i = 0; i < _status.count - 1; ++i)
    {
        res = res[_status[i].integerValue];
    }
    return res;
}

- (id) next
{
    if (_array.count == 0)
    {
        return nil;
    }
    
    NSArray *curArray = self.currentArray;
    NSUInteger nextPos = _status.lastObject.integerValue + 1;
    if (curArray.count > nextPos)
    {
        [_status removeLastObject];
        [_status addObject:@(nextPos)];
        id res = curArray[nextPos];
        if ([res isKindOfClass:[NSArray class]])
        {
            [_status addObject:@(-1)];
            return [self next];
        }
        return res;
    }
    
    if (curArray != _array)
    {
        [_status removeLastObject];
        return [self next];
    }
    
    return nil;
}

+ (void) dfsArray:(NSArray *)targetArray result:(NSMutableArray *)resArray
{
    if (targetArray.count == 0)
    {
        return;
    }
    
    for (id item in targetArray)
    {
        if ([item isKindOfClass:[NSArray class]])
        {
            [self dfsArray:item result:resArray];
        }
        else
        {
            [resArray addObject:item];
        }
    }
}

- (NSArray *) allObjects
{
    NSMutableArray *res = @[].mutableCopy;
    [ArrayIterator dfsArray:_array result:res];
    return res;
}
@end