flutter error: The operator '[]' isn't defined for the class 'Object?

Question

I´m trying to acess the score of a given question:

 main() {
      final questions = const [
        {
          "question": "Your favorite animal?",
          "answer": [
            {"text": "Lion", "score": 4},
            {"text": "Tiger", "score": 6},
          ]
        }
      ];
    
      print(questions[0]["answer"]["score"]);
    }

Here´s how i´m trying to acess it: print(questions[0]["answer"]["score"]);

But it´s showing me an error:

Error: The operator '[]' isn't defined for the class 'Object?'.
 - 'Object' is from 'dart:core'.
Try correcting the operator to an existing operator, or defining a '[]' operator.
  print(questions[0]["answer"]["pontuacao"]);

How can I fix this?

questions[0]["answer"] gives you a list of elements, you need to index into it before calling ["score"]. — mmcdon20
– mmcdon20, Commented Dec 18, 2022 at 20:48

Stefano Leone · Accepted Answer · 2022-12-18 21:36:49Z

2

Until questions[0]["answer"] it's ok. But then, that returns an array, in particular:

[
  {"text": "Lion", "score": 4},
  {"text": "Tiger", "score": 6},
]

So, if you want to print a single score, just add an index like questions[0]["answer"][0]["score"]. Otherwise, if you want to print them all, just use

questions[0]["answer"].map((element) => print(element["score"])

If you want to print ALL questions's scores, do te same for questions array:

questions.map((question) => question["answer"].map((element) => print(element["score"]))

answered Dec 18, 2022 at 21:36

Stefano Leone

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1 Comment

Dennis Castro Over a year ago

Thank you for taking time to answer my question, this is exactly what i needed.

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