Comment puis-je itération sur un tableau d'objets qui appartiennent à une valeur de clé - flotter

Je vous recommande d'utiliser des classes de données pour de telles situations.

import 'package:flutter/material.dart';

List<Anchor> _parseAnchors(Map<String, dynamic> map) {
  final anchors = <Anchor>[];
  for (var anchorMap in map['Anchors']) {
    final anchor = Anchor.fromMap(anchorMap);
    anchors.add(anchor);
  }
  return anchors;
}

class Anchor {
  final int oId;
  final String name;
  final String acronym;
  final List<DistributionCenter> distributionCenters;

  const Anchor({
    @required this.oId,
    @required this.name,
    @required this.acronym,
    @required this.distributionCenters,
  });

  factory Anchor.fromMap(Map<String, dynamic> map) {
    final distributionCenters = <DistributionCenter>[];
    for (var distribution in map['DistributionCentres']) {
      final distributionCenter = DistributionCenter.fromMap(distribution);
      distributionCenters.add(distributionCenter);
    }

    return Anchor(
      oId: map['Oid'] as int,
      name: map['Name'] as String,
      acronym: map['Acronym'] as String,
      distributionCenters: distributionCenters,
    );
  }
}

class DistributionCenter {
  final int id;
  final String name;
  final String address;

  const DistributionCenter({
    @required this.id,
    @required this.name,
    @required this.address,
  });

  factory DistributionCenter.fromMap(Map<String, dynamic> map) {
    return DistributionCenter(
      id: map['Oid'] as int,
      name: map['Name'] as String,
      address: map['Address'] as String,
    );
  }
}

class AnchorPage extends StatelessWidget {
  // details page
  final Anchor anchor;

  @override
  const AnchorPage({Key key, @required this.anchor}) : super(key: key);

  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: Text(anchor.name),
      ),
    );
  }
}

class AnchorsPage extends StatefulWidget {
  const AnchorsPage({Key key}) : super(key: key);

  @override
  _AnchorsPageState createState() => _AnchorsPageState();
}

class _AnchorsPageState extends State<AnchorsPage> {
  static const anchorsMap = {
    "Anchors": [
      {
        "Oid": 11,
        "Name": "MAIZE ASSOCIATION OF NIGERIA",
        "Acronym": "MAAN",
        "DistributionCentres": [
          {
            "Oid": 11,
            "Name": "Logo Centre (Zone A)",
            "Address": "Private Warehouse, Ugba, Logo LGA"
          },
          {
            "Oid": 12,
            "Name": "Makurdi Centre (Zone B)",
            "Address": "Ministry of Agric, Makurdi "
          },
          {
            "Oid": 13,
            "Name": "Oturkpo Centre (Zone C)",
            "Address": "Private Warehouse, Oturkpo"
          },
          {
            "Oid": 15,
            "Name": "Borno MAAN centre",
            "Address": "Bolori Store, Flavour Mill, Behind Vita Foam, Maiduguri"
          },
          {
            "Oid": 18,
            "Name": "Bauchi Centre",
            "Address": "BASPD, Dass Road, Bauchi"
          }
        ],
        "NoOfDistributionCentres": 5
      },
      {
        "Oid": 2,
        "Name":
            "MAIZE GROWERS, PROCESSORS AND MARKETERS ASSOCIATION OF NIGERIA",
        "Acronym": "MAGPAMAN",
        "DistributionCentres": [
          {
            "Oid": 2,
            "Name": "Guma Centre",
            "Address":
                "P 32, 2nd Avenue Federal Housing Estate, N/Bank, Makurdi"
          },
          {
            "Oid": 3,
            "Name": "Logo Centre",
            "Address": "Terhemen Akema Storage Facility, Ugba, Logo LGA"
          },
          {
            "Oid": 5,
            "Name": "Oturkpo Centre",
            "Address": "Grain Store, Lower Benue Okele Project, Otukpo"
          },
          {
            "Oid": 6,
            "Name": "Gboko Centre",
            "Address":
                "K3 New Road, Opposite former coca cola plant. Solar Schools Street, 
    Gboko"
          },
          {
            "Oid": 7,
            "Name": "Gwer East Centre",
            "Address":
                "Ahua Shardye's Warehouse, Behind Sylkan Filling Station, Ikpayongo , 
  G/East LGA"
          },
          {
            "Oid": 8,
            "Name": "Kwande Centre",
            "Address": "KM 3, Adagi Road, Adikpo"
          },
          {
            "Oid": 9,
            "Name": "Ohimini Centre",
            "Address": "Ajoga Oglewu, Ohimini"
          },
          {
            "Oid": 10,
            "Name": "Oju Centre",
            "Address": "Behind Town Hall, Ohuhu owo, Oju LGA"
          }
        ],
        "NoOfDistributionCentres": 8
      }
    ],
  };
  final _anchors = <Anchor>[];

  @override
  Widget build(BuildContext context) {
    // now you can use the anchors list here
    return Scaffold(
      body: ListView.builder(
        itemCount: _anchors.length,
        itemBuilder: (context, index) {
          final anchor = _anchors[index];
          return ListTile(
            title: Text(anchor.name),
            subtitle: Text(anchor.acronym),
            trailing: Text(anchor.distributionCenters?.length?.toString()),
            onTap: () {
              Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) => AnchorPage(anchor: anchor),
                ),
              );
            },
          );
        },
      ),
    );
  }

  @override
  void initState() {
    super.initState();
    final anchors = _parseAnchors(anchorsMap);
    _anchors.addAll(anchors);
  }
}