I'm trying to get two int from JSON file

This is the api response

[
    {
        "New_V": 30,
        "Old_V": 29
    }
]

When I use jsonDecode to get these two int I get an error in the tagged code

I keep getting

Unhandled Exception: type 'String' is not a subtype of type 'int' of 'index'

on the code line

newV = vData['New_V'].toInt();

this is my code

isTheirUpdate() async {
   var vData;
   try {
     Response response =
         await get(Uri.parse('https://0000000000000/check_v.json'));
     if (response.statusCode == 200) {
       vData = jsonDecode(response.body);
       print(vData);
       int newV;
       int oldV;
       setState(() {
         newV = vData['New_V'].toInt(); /////////// I get error here "type 'String' is not a subtype of type 'int' of 'index'"
         oldV = vData['Old_V'].toInt();
       });
       if (newV == KCheckAppVersion) {
         isTheirInternet;
       } else if (oldV == KCheckAppVersion) {
         showDialog()
       } else {
         showDialog()
       }
     }
   } on SocketException catch (_) {}
 }

There is something I miss but I don't know what it is Can someone explain the reason and a fix for this line of code?

Thanks

CodePudding user response：

It looks like the issue is with the type of the vData variable. It appears that the vData variable is being set to the result of jsonDecode, which will return a Map<String, dynamic> containing the JSON data. However, the code is trying to access elements in the vData map using string keys, like vData['New_V'], as if it were a list.

To fix the issue, you can try changing the line of code that sets the vData variable to:

vData = jsonDecode(response.body) as Map<String, dynamic>;

This will explicitly cast the result of jsonDecode to the correct type, a Map<String, dynamic>. Then, you can access the values in the map using the correct syntax, like vData['New_V'].

For example, the following code should work:

setState(() {
  newV = vData['New_V'];
  oldV = vData['Old_V'];
});

I hope this helps! Let me know if you have any questions.

CodePudding user response：

Your variable are string and you can't use toInt() on string, try this way to parse to int:

newV = int.parse(vData[0]['New_V'].toString());
oldV = int.parse(vData[0]['Old_V'].toString());

also you are getting list of map not a single map so vData is list of map and you need to use it like this:

if((vData as List).isNotEmpty){
   setState(() {
      newV = int.parse(vData[0]['New_V'].toString());
      oldV = int.parse(vData[0]['Old_V'].toString());
   });
}