How to convert json empty array in Flutter?

Question

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.

Solution

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"];
}

Comments

[pskink]

final jsonString = '{"data": []}'; final jsonDecoded = json.decode(jsonString); final List<dynamic> data = jsonDecoded['data']; print(data.runtimeType); print(data);

[Chen Li Yong]

@pskink nvm, 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": {}.

[Chen Li Yong]

I see. Then that means it's not considered good practice to assign empty Json field data into Dart variable. Thanks!

[Jahidul Islam]

but you will get the empty JSON, when JSON is empty it returns a dynamic list. So it would be good to check first

[Chen Li Yong]

After some investigation, turns out Dart code is right. As the "data" was a field in an object, within a list of objects, turns out one object does have a "data": { }.