How to convert json empty array in Flutter?-CodePudding

EDIT: after I check again, as this is a field within an object within a list, turns out somewhere in the list, one object does actually having "data": {}

Closed question. Thanks for helping.

I have a json field with contents of empty array:

{
  "data": [ ]
}

The problem is when I tried to put it into a list, it throws a fit.

List<dynamic> result = json["data"];

type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'List<dynamic>'

When I see it's "internal linked hash map", I thought then maybe I can use a Map. So I changed the receiver type as Map.

Map<String, dynamic> result = json["data"];

type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'

Why is this happening?

The only way I can finally resolve this is by creating a type-inferred variable as an intermediate:

var temp = json["data"];
print("temp's runtime type: ${temp.runtimeType}");  // List<dynamic>
List<dynamic> result = temp;  // works

I know this is resolved using workaround for now, but I just want to know why the attempt above is error, and how can I straightly assign the json field content into explicitly-typed variable.

CodePudding user response：

At first, you just check your data is empty or not empty then assign the value to your map.

Map<String, dynamic> result;
if(json["data"]!=null && json["data"].isNotEmpty){
   result = json["data"];
}

CodePudding user response：

Dart compiler thinks that the result could be null so it is throwing errors, if you are sure that it will not be null then you could do this.

  //This json is of type Map<String, List<dynamic>>
  final json = {"data": []};

  if (json["data"] != null) {

    // i have used ! operator here after ["data"]
    List l = json["data"]!;

  }

or if you are not sure about the data then you can use what @Jahidul Islam has shown.