How to show image from model to carousel(slider) in flutter?

Question

I have json response from API and I want to display it in a carouselslider. here is my response from API

[
  {
    "header": "Header 1",
    "subheader": "",
    "content": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. In laoreet vestibulum condimentum. Nunc finibus porttitor purus, in volutpat ante luctus in.",
    "imageurl": "https://www.bannerbatterien.com/upload/filecache/Banner-Batterien-Windrder2-web_06b2d8d686e91925353ddf153da5d939.webp",
    "footer": "Footer 1",
    "releasedate": "01 Aug 2019",
    "bodyimage": ""
  },
  {
    "header": "Header 2",
    "subheader": "",
    "content": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. In laoreet vestibulum condimentum. Nunc finibus porttitor purus, in volutpat ante luctus in.",
    "imageurl": "https://i.pinimg.com/originals/0b/a3/d6/0ba3d60362c7e6d256cfc1f37156bad9.jpg",
    "footer": "Footer 2",
    "releasedate": "06 Sep 2019",
    "bodyimage": ""
  }
]

I have declare List<NewsPromotion> imgSlider; and when I got my response from API, I'm trying to insert it into my model imgSlider = menuModel[3].news_promotion; and try to call it

class NewsPromotion {
  String header;
  String subheader;
  String content;
  String imageurl;
  String footer;
  String releasedate;
  String bodyimage;

  NewsPromotion(
    this.header,
    this.subheader,
    this.content,
    this.imageurl,
    this.footer,
    this.releasedate,
    this.bodyimage,
  );
  factory NewsPromotion.fromJson(dynamic json) {
    return NewsPromotion(
      json['header'] as String,
      json['subheader'] as String,
      json['content'] as String,
      json['imageurl'] as String,
      json['footer'] as String,
      json['releasedate'] as String,
      json['bodyimage'] as String,
    );
  }
  @override
  String toString() {
    return '{ ${this.header} ,${this.subheader} ,${this.content} ,${this.imageurl} ,${this.footer} ,${this.releasedate} ,${this.bodyimage}}';
  }
}

final CarouselSlider autoPlayImage = CarouselSlider(
    options: CarouselOptions(
      height: 180.0,
      autoPlay: true,
      enlargeCenterPage: true,
      aspectRatio: 16 / 9,
    ),
    items: imgSlider.map((fileImage) {
      return Builder(
        builder: (BuildContext context) {
          return Container(
            margin: EdgeInsets.all(5.0),
            child: GestureDetector(
              child: Image.asset(
                'assets/${fileImage}',
                width: 10000,
                fit: BoxFit.cover,
              ),
              onTap: () {
                //
              },
            ),
          );
        },
      );
    }).toList(),
  );

But it give me errror

The instance member 'imgSlider' can't be accessed in an initializer. Try replacing the reference to the instance member with a different expression