'List<dynamic>' 类型不是 'List<String>' 类型的子类型

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();

来自 API“http://192.168.0.102:5000/get_location_names”的 Json 数据

{
"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",
 ]
}

我想在下拉字段中传递这个 json 数据。DropDownFeild 是第三方小部件，它在其名为“items”的属性中将数据作为字符串列表，但我面临这个错误。请帮助我，让我明白我哪里出错了。

════════ 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

Answer 1

我想以下修复会有所帮助：

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

这是因为 dart 将 locationDataBangalore["locations"] 的值视为动态值列表，因此您应该将它们转换为字符串。