dart - 未捕获的TypeError:无法在dart中读取nullError的属性 'getInitialConfig'

Question

**我是新手，我在这里使用适配器模式，我不知道何时我调用getInitialConfig方法调用主方法时该方法返回null请给我一个帮助**

class below

import 'dart:convert';

// team attribute
class TeamAttributes {
  String teamName;
  int numOfPlayers;
  int wkPlayer;
  int captainPlayer;
  int currentIndex;
  List<String> teamPlayerList = new List<String>();

  TeamAttributes({
    this.teamName,
    this.numOfPlayers,
    this.wkPlayer,
    this.captainPlayer,
    this.currentIndex,
    this.teamPlayerList,
  });



  factory TeamAttributes.fromJson(Map<String, dynamic> json) {
    return TeamAttributes(
      teamName: json['teamName'],
      numOfPlayers: json['numOfPlayers'],
      wkPlayer: json['wkPlayer'],
      captainPlayer: json['captainPlayer'],
      currentIndex: json['currentIndex'],
      teamPlayerList: parseList(json['teamPlayerList']), // json['places']);
    );
  }



  Map<String, dynamic> toJson() {
    return {
      'teamName': teamName,
      "numOfPlayers": numOfPlayers,
      "wkPlayer": wkPlayer,
      "captainPlayer": captainPlayer,
      "currentIndex": currentIndex,
      "teamPlayerList": teamPlayerList,
    };
  }

  static List<String> parseList(teamPlayerJson) {
    List<String> teamPlayerList = new List<String>.from(teamPlayerJson);
    return teamPlayerList;
  }
}

///setting
class QuickStartSettings {
  String matchName;
  final BattingRestrictions battingRestrictions;
  final BowlingRestrictions bowlingRestrictions;
  final Overs overs;
  final Balls balls;
  final Wides wides;
  final NoBalls noBalls;
  final Wickets wickets;

  QuickStartSettings({
    this.matchName,
    this.battingRestrictions,
    this.bowlingRestrictions,
    this.overs,
    this.balls,
    this.wides,
    this.noBalls,
    this.wickets,
  });

  factory QuickStartSettings.fromJson(Map<String, dynamic> json) {
    return QuickStartSettings(
      matchName: json['matchName'],
      battingRestrictions:
          BattingRestrictions.fromJson(json['battingRestrictions']),
      bowlingRestrictions:
          BowlingRestrictions.fromJson(json['bowlingRestrictions']),
      overs: Overs.fromJson(json['overs']),
      balls: Balls.fromJson(json['balls']),
      wides: Wides.fromJson(json['wides']),
      noBalls: NoBalls.fromJson(json['noBalls']),
      wickets: Wickets.fromJson(json['wickets']),
    );
  }
  Map<String, dynamic> toJson() {
    return {
      'matchName': matchName,
      "battingRestrictions": battingRestrictions,
      'bowlingRestrictions': bowlingRestrictions,
      "overs": overs,
      "balls": balls,
      "wides": wides,
      "noBalls": noBalls,
      "wickets": wickets,
    };
  }
}

class Wickets {
  bool isWicketDismissal;
  bool allowBatAgain;
  bool lastManStand;
  int battingTeamWicketPenalty;
  int bowlingTeamWicketBonus;

  Wickets({
    this.isWicketDismissal,
    this.allowBatAgain,
    this.lastManStand,
    this.battingTeamWicketPenalty,
    this.bowlingTeamWicketBonus,
  });
  factory Wickets.fromJson(Map<String, dynamic> json) {
    return Wickets(
      isWicketDismissal: json['isWicketDismissal'],
      allowBatAgain: json['allowBatAgain'],
      lastManStand: json['lastManStand'],
      battingTeamWicketPenalty: json['battingTeamWicketPenalty'],
      bowlingTeamWicketBonus: json['bowlingTeamWicketBonus'],
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'isWicketDismissal': isWicketDismissal,
      "allowBatAgain": allowBatAgain,
      'lastManStand': lastManStand,
      "battingTeamWicketPenalty": battingTeamWicketPenalty,
      "bowlingTeamWicketBonus": bowlingTeamWicketBonus,
    };
  }
}

class NoBalls {
  bool alwaysRebowl;
  bool rebowlLastBall;
  bool rebowlForLastOver;
  int noBallValue;
  bool isBallFacedCountedForBatsman;

  NoBalls({
    this.alwaysRebowl,
    this.rebowlLastBall,
    this.rebowlForLastOver,
    this.noBallValue,
    this.isBallFacedCountedForBatsman,
  });
  factory NoBalls.fromJson(Map<String, dynamic> json) {
    return NoBalls(
      alwaysRebowl: json['alwaysRebowl'],
      rebowlLastBall: json['rebowlLastBall'],
      rebowlForLastOver: json['rebowlForLastOver'],
      noBallValue: json['noBallValue'],
      isBallFacedCountedForBatsman: json['isBallFacedCountedForBatsman'],
    );
  }
  Map<String, dynamic> toJson() {
    return {
      'alwaysRebowl': alwaysRebowl,
      "rebowlLastBall": rebowlLastBall,
      'rebowlForLastOver': rebowlForLastOver,
      "noBallValue": noBallValue,
      "isBallFacedCountedForBatsman": isBallFacedCountedForBatsman,
    };
  }
}

class Wides {
  bool alwaysRebowl;
  bool rebowlLastBall;
  bool rebowlForLastOver;
  int wideValue;
  bool isBallFacedCountedForBatsman;

  Wides({
    this.alwaysRebowl,
    this.rebowlLastBall,
    this.rebowlForLastOver,
    this.wideValue,
    this.isBallFacedCountedForBatsman,
  });
  factory Wides.fromJson(Map<String, dynamic> json) {
    return Wides(
      alwaysRebowl: json['alwaysRebowl'],
      rebowlLastBall: json['rebowlLastBall'],
      rebowlForLastOver: json['rebowlForLastOver'],
      wideValue: json['wideValue'],
      isBallFacedCountedForBatsman: json['isBallFacedCountedForBatsman'],
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'alwaysRebowl': alwaysRebowl,
      "rebowlLastBall": rebowlLastBall,
      'rebowlForLastOver': rebowlForLastOver,
      "wideValue": wideValue,
      "isBallFacedCountedForBatsman": isBallFacedCountedForBatsman,
    };
  }
}

class Balls {
  int ballsPerOver;
  int ballsLastOver;

  Balls({
    this.ballsPerOver,
    this.ballsLastOver,
  });
  factory Balls.fromJson(Map<String, dynamic> json) {
    return Balls(
      ballsPerOver: json['ballsPerOver'],
      ballsLastOver: json['ballsLastOver'],
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'ballsPerOver': ballsPerOver,
      "ballsLastOver": ballsLastOver,
    };
  }
}

class Overs {
  int numOfOvers;
  bool isUnlimitedOvers;

  Overs({
    this.numOfOvers,
    this.isUnlimitedOvers,
  });
  factory Overs.fromJson(Map<String, dynamic> json) {
    return Overs(
      numOfOvers: json['numOfOvers'],
      isUnlimitedOvers: json['isUnlimitedOvers'],
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'numOfOvers': numOfOvers,
      "isUnlimitedOvers": isUnlimitedOvers,
    };
  }
}

class BowlingRestrictions {
  bool maxOverWarning;
  int maxOverWarningCount;

  BowlingRestrictions({
    this.maxOverWarning,
    this.maxOverWarningCount,
  });
  factory BowlingRestrictions.fromJson(Map<String, dynamic> json) {
    return BowlingRestrictions(
      maxOverWarning: json['maxOverWarning'],
      maxOverWarningCount: json['maxOverWarningCount'],
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'maxOverWarning': maxOverWarning,
      "maxOverWarningCount": maxOverWarningCount,
    };
  }
}

class BattingRestrictions {
  bool maxBallWarning;
  int maxBallWarningCount;

  bool maxOverWarning;
  int maxOverWarningCount;

  bool maxRunsWarning;
  int maxRunsWarningCount;

  bool forceRetAfterWarning;

  BattingRestrictions({
    this.maxBallWarning,
    this.maxBallWarningCount,
    this.maxOverWarning,
    this.maxOverWarningCount,
    this.maxRunsWarning,
    this.maxRunsWarningCount,
    this.forceRetAfterWarning,
  });
  factory BattingRestrictions.fromJson(Map<String, dynamic> json) {
    return BattingRestrictions(
      maxBallWarning: json['maxBallWarning'],
      maxBallWarningCount: json['maxBallWarningCount'],
      maxOverWarning: json['maxOverWarning'],
      maxOverWarningCount: json['maxOverWarningCount'],
      maxRunsWarning: json['maxRunsWarning'],
      maxRunsWarningCount: json['maxRunsWarningCount'],
      forceRetAfterWarning: json['forceRetAfterWarning'],
    );
  }
  Map<String, dynamic> toJson() {
    return {
      'maxBallWarnings': maxBallWarning,
      "maxBallWarningCount": maxBallWarningCount,
      "maxOverWarning": maxOverWarning,
      "maxOverWarningCount": maxOverWarningCount,
      "maxRunsWarnings": maxRunsWarning,
      "maxRunsWarningCount": maxRunsWarningCount,
      "forceRetAfterWarning": forceRetAfterWarning,
    };
  }
}

// QuickStartModel

class QuickStartModel {
  final TeamAttributes leftTeam;
  final TeamAttributes rightTeam;
  final QuickStartSettings settings;
  String tossWonBy;
  String tossDecision;

  QuickStartModel({
    this.tossWonBy,
    this.tossDecision,
    this.leftTeam,
    this.rightTeam,
    this.settings,
  });
  factory QuickStartModel.fromJson(Map<String, dynamic> json) {
    return QuickStartModel(
      leftTeam: TeamAttributes.fromJson(json['leftTeam']),
      rightTeam: TeamAttributes.fromJson(json['rightTeam']),
      settings: QuickStartSettings.fromJson(json['settings']),
      tossWonBy: json['tossWonBy'],
      tossDecision: json['tossDecision'],
    );
  }
  Map<String, dynamic> toJson() {
    return {
      'leftTeam': leftTeam,
      "rightTeam": rightTeam,
      "settings": settings,
      "tossWonBy": tossWonBy,
      "tossDecision": tossDecision,
    };
  }
}

moke json class below

//moke Api
class QuickStartApi {
  final String _quickStartJson = '''
  {
  "tossDecision": "xs",
  "tossWonBy": "as",
  "leftTeam": {
    "teamName": "Team A",
    "numOfPlayers": 11,
    "wkPlayer": 1,
    "captainPlayer": 1,
    "currentIndex": 1,
    "teamPlayerList": [
      "Player 1",
      "Player 2",
      "Player 3",
      "Player 4",
      "Player 5",
      "Player 6",
      "Player 7",
      "Player 8",
      "Player 9",
      "Player 10",
      "Player 11"
    ]
  },
  "rightTeam": {
    "teamName": "Team B",
    "numOfPlayers": 11,
    "currentIndex": 1,
    "captainPlayer": 1,
    "wkPlayer": 1,
    "teamPlayerList": [
      "Player 1",
      "Player 2",
      "Player 3",
      "Player 4",
      "Player 5",
      "Player 6",
      "Player 7",
      "Player 8",
      "Player 9",
      "Player 10",
      "Player 11"
    ]
  },
  "settings": {
    "matchName": 'FootBall',
    "battingRestrictions": {
      "maxBallWarning": true,
      "maxBallWarningCount": 5,
      "maxOverWarning": true,
      "maxOverWarningCount": 7,
      "maxRunsWarning": true,
      "maxRunsWarningCount": 9,
      "forceRetAfterWarning": true
    },
    "bowlingRestrictions": { "maxOverWarning": true, "maxOverWarningCount": 5 },
    "overs": { "isUnlimitedOvers": true, "numOfOvers": 10 },
    "balls": { "ballsLastOver": 1, "ballsPerOver": 1 },
    "wides": {
      "alwaysRebowl": true,
      "rebowlLastBall": false,
      "rebowlForLastOver": false,
      "wideValue": 10,
      "isBallFacedCountedForBatsman": false
    },
    "noBalls": {
      "alwaysRebowl": true,
      "rebowlLastBall": false,
      "rebowlForLastOver": false,
      "noBallValue": 10,
      "isBallFacedCountedForBatsman": false
    },
    "wickets": {
      "isWicketDismissal": true,
      "allowBatAgain": true,
      "lastManStand": false,
      "battingTeamWicketPenalty": 5,
      "bowlingTeamWicketBonus": 5
    }
   }
  }
  ''';

  String getQuickStartJson() {
    return _quickStartJson;
  }
}

Adapater pattern abstract class below

//Adapater

abstract class QuickStartAdapter {
  QuickStartModel getInitialConfig();
}

abstract class implement below

//adapter impl

class QuickStartRemote extends QuickStartAdapter {
  final QuickStartApi _api = QuickStartApi();

  @override
  QuickStartModel getInitialConfig() {
    var quickStartJSON = _api.getQuickStartJson();
    var quickStartList = _parseQuickStartJson(quickStartJSON);
    print(quickStartList);
    return quickStartList;
  }

  QuickStartModel _parseQuickStartJson(String quickStartJSON) {
    // final Map<String, dynamic> quickStartDecodedJson =
    //     json.decode(quickStartJSON);
    var quickStartDecodedJson =
        json.decode(quickStartJSON) as Map<String, dynamic>;
    print(quickStartDecodedJson);
    var quickStartModel = QuickStartModel.fromJson(quickStartDecodedJson);
    print(quickStartModel.settings.matchName);
    return quickStartModel;
  }
}

main method call getInitialConfig method below

void main() {
  QuickStartAdapter adapter;

  adapter.getInitialConfig();
  QuickStartModel abc = adapter.getInitialConfig();
print(abc);


}

Answer 1

因为您从未将adapter变量分配给任何值，所以您可以在这里找到问题。

void main() {
  QuickStartAdapter adapter; // <- your problem

  adapter.getInitialConfig();
  QuickStartModel abc = adapter.getInitialConfig();
}

您需要创建一个从 QuickStartAdapter继承的类的实例(因为该类本身是 abstract并将其分配给 adapter变量。

这是解决方案的示例，其中您创建 QuickStartRemote实例(从QuickStartAdapter扩展而来)并将其分配给变量:

void main() {
  QuickStartAdapter adapter = QuickStartRemote();

  adapter.getInitialConfig();
  QuickStartModel abc = adapter.getInitialConfig();
  print(abc);
}

更改之后，我还在JSON模拟数据中发现了一个错误，其中:

"matchName": 'FootBall', 

本来应该:

"matchName": "FootBall",

经过这两个修复，它可以在我的机器上运行。