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

Question

import 'package:flutter/material.dart';
import 'package:dropdownfield/dropdownfield.dart';
import 'package:http/http.dart' as http;

class Formwidget extends StatefulWidget {

  @override
  _FormwidgetState createState() => _FormwidgetState();
}

class _FormwidgetState extends State<Formwidget> {


  Map locationDataBangalore;
  fetchlocationData()async{
    http.Response locationData = await http.get("http://192.168.0.102:5000/get_location_names");
    setState(() {
      locationDataBangalore = jsonDecode(locationData.body);
    });
    print(locationDataBangalore['locations']);
  }
  @override
  void initState() {
    fetchlocationData();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return locationDataBangalore == null ? Center(child: CircularProgressIndicator(),) :Container(
      child: Column(
        children: <Widget>[
          DropDownField(
            controller: locationController,
            hintText: "Select Location",
            enabled: true,
            items: locationDataBangalore["locations"],
          ),
        ],
      ),
    );
  }
}

final locationController = TextEditingController();

Json Data that is comming from the API "http://192.168.0.102:5000/get_location_names"

{
"locations": [
"1st block jayanagar",
"1st phase jp nagar",
"2nd phase judicial layout",
"2nd stage nagarbhavi",
"5th block hbr layout",
"5th phase jp nagar",
"6th phase jp nagar",
"7th phase jp nagar",
"8th phase jp nagar",
"9th phase jp nagar",
"aecs layout",
 ]
}

I want to pass this json data in the dropdown feild.The DropDownFeild is a third party Widget and it take data as List of String in its property called as "items" But i am facing this Error. Please Help me and make me understand where i am going wrong.

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following _TypeError was thrown building DropDownField(dirty, dependencies: [MediaQuery], state: DropDownFieldState#b3785):
type 'List<dynamic>' is not a subtype of type 'List<String>'

The relevant error-causing widget was: 
  DropDownField file:///home/sidd/AndroidStudioProjects/home_price_predictor/lib/widgets/formWidget.dart:38:11
When the exception was thrown, this was the stack: 
#0      DropDownFieldState._items (package:dropdownfield/dropdownfield.dart:200:30)
#1      new DropDownField.<anonymous closure> (package:dropdownfield/dropdownfield.dart:175:71)
#2      FormFieldState.build (package:flutter/src/widgets/form.dart:526:26)
#3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4792:27)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4675:15)
...
════════════════════════════════════════════════════════════════════════════════════════════════════
I/SurfaceView(18574): updateWindow -- setFrame, this = io.flutter.embedding.android.FlutterSurfaceView{343db9e V.E...... ......I. 0,0-720,1280}
I/SurfaceView(18574): updateWindow -- OnPreDrawListener, mHaveFrame = true, this = io.flutter.embedding.android.FlutterSurfaceView{343db9e V.E...... ......I. 0,0-720,1280}

════════ Exception caught by rendering library ═════════════════════════════════════════════════════
A RenderFlex overflowed by 99551 pixels on the bottom.
The relevant error-causing widget was: 
  Column file:///home/sidd/AndroidStudioProjects/home_price_predictor/lib/pages/formpage.dart:32:16
════════════════════════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
type 'List<dynamic>' is not a subtype of type 'List<String>'
The relevant error-causing widget was: 
  DropDownField file:///home/sidd/AndroidStudioProjects/home_price_predictor/lib/widgets/formWidget.dart:38:11
════════════════════════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
type 'List<dynamic>' is not a subtype of type 'List<String>'
The relevant error-causing widget was: 
  DropDownField file:///home/sidd/AndroidStudioProjects/home_price_predictor/lib/widgets/formWidget.dart:38:11
════════════════════════════════════════════════════════════════════════════════════════════════════
V/InputMethodManager(18574): START INPUT: io.flutter.embedding.android.FlutterView{b02d67f VFE...... .F....I. 0,0-720,1280} ic=null tba=android.view.inputmethod.EditorInfo@d855bb2 controlFlags=#100
D/ActivityThread(18574): ACT-AM_ON_PAUSE_CALLED ActivityRecord{c04ff16 token=android.os.BinderProxy@4dd8097 {com.example.homepricepredictor/com.example.homepricepredictor.MainActivity}}
D/ActivityThread(18574): ACT-PAUSE_ACTIVITY handled : 0 / android.os.BinderProxy@4dd8097
V/ActivityThread(18574): Finishing stop of ActivityRecord{c04ff16 token=android.os.BinderProxy@4dd8097 {com.example.homepricepredictor/com.example.homepricepredictor.MainActivity}}: show=true win=com.android.internal.policy.PhoneWindow@1647703
D/ActivityThread(18574): ACT-STOP_ACTIVITY_SHOW handled : 0 / android.os.BinderProxy@4dd8097

Solution

I suppose following fix would help:

...
DropDownField(
            controller: locationController,
            hintText: "Select Location",
            enabled: true,
            items: locationDataBangalore["locations"].cast<String>(),
          ),
...

This happens because dart treats value of locationDataBangalore["locations"] as list of dynamic values, so you should cast them to String.

Comments

[Siddharth]

Thanks @Alex Radzishevsky This worked .I also understood the Concept Thanks !