breaking exception '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, String>'

Question

I ran a flutter upgrade today...

I'm now on v0.2.11 and I'm getting a strange runtime error in this function:

Future apiCall([Map params = const {}]) async {
  loading = true;
  Map stringParams = {};
  params.forEach((k,v)=>stringParams[k.toString()] = v.toString());
  Uri url = new Uri.https(apiDomain, apiPath, stringParams);
  print(url);
  var result = await http.post(
    url,
    body: {'apikey': apiKey}
  );
  loading = false;
  print(result.body);
  return json.decode(result.body);
}

I'm calling the function without any params and I get the subtype error.

This code works in DartPad.

Does anyone have an idea what might be going on?

This isn't an answer in and of itself, but this page might be of help for you to understand the new type-safe features in Dart 2.0. — rmtmckenzie
– rmtmckenzie, Commented Apr 13, 2018 at 20:06

Jonah Williams · Accepted Answer · 2018-04-13 20:04:28Z

23

The constructor for Uri.https requires a Map with a runtime type of Map<String, String>. When you create stringParams without any type annotations, you are actually creating a Map<dynamic, dynamic>. The correct way to create this for Dart 2 is

Map<String, String> stringParams = {};
// or
var stringParams = <String, String>{};

The reason this used to work is that in Dart 1, even in strong mode, dynamic was fuzzy and acted like both Object and null - meaning a dynamic type was assignable to and from anything. In Dart 2, dynamic acts just like Object, except you can call methods or access properties on it without a downcast.

answered Apr 13, 2018 at 20:04

Jonah Williams

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1 Comment

neerav94 Over a year ago

What happens if my object is of type Map<String, dynamic>. How to make a post request in that case? It keeps giving the above mentioned error.

Mohammed · Accepted Answer · 2018-11-29 21:21:37Z

12

I used this

    if(json["key"]!= null){
       this.active_guests = json["key"].cast<String, int>();
     }

answered Nov 29, 2018 at 21:21

Mohammed

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1 Comment

Joel Hernandez Over a year ago

How about nested maps :'(

Amir Ajorloo · Accepted Answer · 2019-09-02 11:05:14Z

1

You can send nested JSON params like this:

Convert it to a string using json.encode.
Send "Content-Type:application/json" in header.

var uri = "${Config.baseURL}/your/endpoint";
var headers = {
  'Content-Type': 'application/json'
};
final response = await http.post(
  uri,
  body: json.encode(data),
  headers: headers
);

answered Sep 2, 2019 at 11:05

Amir Ajorloo

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