如何修复 NoSuchMethodError：在 null 上调用了方法 \'[]\'？

Question

我有一个函数可以过滤来自 api 的数据并将过滤后的数据设置为新地图：

_addUpAndGetPercentage(List states) {

  Map<String, dynamic> _states = {
    "Stress": [],
    "Fatigue": [],
    "Anxiety": [],
    "Relaxation": [],
    "Involvement": []
  };

  log("states === $states");  // states === [{externalSessionId: 19dd1148-97e3-4e33-8cd6-9d4ab3b8d64c, iaf: 11, iapf: 9, startTime: null, endTime: null, states: {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}}, {externalSessionId: d1d6637a-a445-467d-b658-91e42b080ed6, iaf: 12, iapf: 8, startTime: null, endTime: null, states: {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}}]

  for (int i = 0; i < states.length; i++) {

    var shortcut = states[i]["states"];

    log("Stress ==== ${states[i]['states'].toString()}");

    if (states[i]["Stress"] != null) {
      _states[i]["Stress"].add(states[i]["Stress"]);
    } else {
      log("ERROOROROROOROR ==== ${states[i]['states'].toString()}");
      _states["Stress"].add(0);
    }

    if (shortcut["Anxiety"] != null) {
      _states["Anxiety"].add(shortcut["Anxiety"]);
    } else {
      _states["Anxiety"].add(0);
    }
  }

  log("_states ===== ${_states.toString()}");

  return _states;
}

当我更改时出现错误状态[i][“压力”]至捷径[“压力”]=>NoSuchMethodError：在 null 上调用了方法“[]”。

但是 log("Stress ==== ${states[i]['states'].toString()}"); 返回我 Stress ==== {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}

捷径[“焦虑”]工作正常，不会给我返回一个错误，只有捷径[“压力”]我不明白为什么..

如果我删除捷径[“压力”]并设置状态[i][“压力”]然后没有出现错误，但它没有像我想要的那样工作，这是我设置时的日志状态[i][“压力”]:

states === [{externalSessionId: 19dd1148-97e3-4e33-8cd6-9d4ab3b8d64c, iaf: 11, iapf: 9, startTime: null, endTime: null, states: {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}}, {externalSessionId: d1d6637a-a445-467d-b658-91e42b080ed6, iaf: 12, iapf: 8, startTime: null, endTime: null, states: {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}}]
[log] Stress ==== {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}
[log] ERROOROROROOROR ==== {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}
[log] Stress ==== {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}
[log] ERROOROROROOROR ==== {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}

[log] _states ===== {Stress: [0, 0], Anxiety: [2, 5]}
states === [{externalSessionId: 19dd1148-97e3-4e33-8cd6-9d4ab3b8d64c, iaf: 11, iapf: 9, startTime: null, endTime: null, states: {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}}, {externalSessionId: d1d6637a-a445-467d-b658-91e42b080ed6, iaf: 12, iapf: 8, startTime: null, endTime: null, states: {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}}]
[log] Stress ==== {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}
[log] ERROOROROROOROR ==== {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}
[log] Stress ==== {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}
[log] ERROOROROROOROR ==== {Stress: 1, Involvement: 1, Slight Fatigue: 2, Anxiety: 5, Relaxation: 2, Chronic Fatigue: 3}
[log] _states ===== {Stress: [0, 0], Anxiety: [2, 5]}

压力应为 [1,1]

如果我添加：

if (shortcut["Involvement"] != null) {
      _states["Involvement"].add(shortcut["Involvement"]);
    } else {
      _states["Involvement"].add(0);
    }

然后这种参与正常工作，如果增加放松然后放松像压力一样返回我的空错误..

Answer 1

我相信因为压力是states: {Anxiety: 2, Stress: 1, Chronic Fatigue: 1}的一部分

而不是这个：

 if (states[i]["Stress"] != null) {
      _states[i]["Stress"].add(states[i]["Stress"]);
    } else {
      log("ERROOROROROOROR ==== ${states[i]['states'].toString()}");
      _states["Stress"].add(0);
    }

你应该有这个：

 if (states[i]["states"]["Stress"] != null) {
      _states[i]["Stress"].add(states[i]["states"]["Stress"]);
    } else {
      log("ERROOROROROOROR ==== ${states[i]['states'].toString()}");
      _states["Stress"].add(0);
    }