Access values in nested dictionary in dart-CodePudding

I am basically trying to access a value inside a dictionary that is inside another one.

void main() {
var results = {
  'usd' : {"first": 2, "second": 4},
  'eur' : 4.10, 
  'gbp' : 4.90, 
  };

  print(results['usd']["first"]);

}

The issue is I am facing that I get an error:

Error: The operator '[]' isn't defined for the class 'Object?'.

'Object' is from 'dart:core'.
print(results['usd']["first"]);

I cannot find the explanation for it, and how to fix it.

Thank you in advance.

CodePudding user response：

The issue arises because your results map has values of different types. Euro and Pound are doubles, but Dollar is a map. So the compiler can't infer a better type for results than Map<String, Object>. You need to give it some help, by telling it the type of type of the usd value.

void main() {
  var results = {
    'usd': {
      'first': 2,
      'second': 4,
    },
    'eur': 4.10,
    'gbp': 4.90,
  };

  final usd = results['usd'] as Map<String, dynamic>;
  print(usd['first']);
}

CodePudding user response：

change the type to Map like:

void main() {
Map results = {
  'usd' : {"first": 2, "second": 4},
  'eur' : 4.10, 
  'gbp' : 4.90, 
  };

  print(results['usd']['first'].toString());

}