【发布时间】：2021-07-13 00:27:00
【问题描述】：
我是一个 Flutter 初学者开发者，我目前正在使用 Flutter 和 Dart 开发一个 BMI 计算器应用程序。实际上，在我的代码中，我面临以下错误。
error: Non-nullable instance field 'result' must be initialized at [bmi_app] lib\calresult.dart:16)error: The body might complete normally, causing 'null' to be returned, but the return type is a potentially non-nullable type. (body_might_complete_normally at [bmi_app] lib\calresult.dart:16)
这是我的 main.dart 文件：
import 'package:bmi_app/calresult.dart';
import 'package:bmi_app/resultscreen.dart';
import 'package:flutter/material.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
enum Gender {
male,
female,
}
void main() {
runApp(MaterialApp(
theme: ThemeData(
primaryColor: Color(0xFF24232F),
accentColor: Color(0XFF1F1E29),
scaffoldBackgroundColor: Color(0xFF2F2E3A),
),
debugShowCheckedModeBanner: false,
home: InputScreen()
)
);
}
class InputScreen extends StatefulWidget {
const InputScreen({Key? key}) : super(key: key);
@override
_InputScreenState createState() => _InputScreenState();
}
class _InputScreenState extends State<InputScreen> {
Color inactiveColor = Color(0xFF24232F);
Color activeColor = Colors.blueGrey;
Gender selectedGender = Gender.values.single;
int height = 100;
int weight = 50;
int age = 15;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Center(
child: Text(
"BMI Calculator"
),
),
),
body: Column(
children: [
Expanded(
child: Row(
children: [
Expanded(
child: GestureDetector(
onTap: () {
setState(() {
selectedGender = Gender.male;
});
},
child: Container(
padding: EdgeInsets.all(10.0),
margin: EdgeInsets.all(10.0),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12.0),
color: selectedGender == Gender.male
? activeColor
: inactiveColor
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Icon(
FontAwesomeIcons.male,
color: Colors.white,
size: 45.0,
),
SizedBox(
height: 10.0,
),
Text(
"Male",
style: TextStyle(
color: Colors.grey,
fontSize: 20.0,
fontWeight: FontWeight.w500,
),
)
],
),
),
),
),
Expanded(
child: GestureDetector(
onTap: () {
setState(() {
selectedGender = Gender.female;
});
},
child: Container(
padding: EdgeInsets.all(10.0),
margin: EdgeInsets.all(10.0),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12.0),
color: selectedGender == Gender.female
? activeColor
: inactiveColor
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Icon(
FontAwesomeIcons.female,
color: Colors.white,
size: 45.0,
),
SizedBox(
height: 10.0,
),
Text(
"Female",
style: TextStyle(
color: Colors.grey,
fontSize: 20.0,
fontWeight: FontWeight.w500,
),
)
],
),
),
),
)
],
),
),
SizedBox(
height: 10.0,
),
Expanded(
child: Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12.0),
color: inactiveColor
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Text(
"HEIGHT",
style: TextStyle(
fontSize: 16.0,
color: Colors.white,
),
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.baseline,
textBaseline: TextBaseline.alphabetic,
children: [
Text(
height.toString(),
style: TextStyle(
color: Colors.white,
fontSize: 35.0,
fontWeight: FontWeight.bold,
)
),
Text(
"cm",
style: TextStyle(
fontSize: 18.0,
color: Colors.white,
),
)
],
),
SliderTheme(data: SliderTheme.of(context).copyWith(
activeTrackColor: Colors.white,
overlayColor: Color(0x291DE9B6),
inactiveTrackColor: Colors.grey,
thumbShape: RoundSliderThumbShape(
enabledThumbRadius: 16.0
),
overlayShape: RoundSliderOverlayShape(
overlayRadius: 30.0
),
thumbColor: Color(0xFF1DE9B6),
),
child: Slider(
value: height.toDouble(),
min: 50.0,
max: 300.0,
onChanged: (double v){
setState(() {
height = v.round();
});
},
)
)
],
),
),
),
Expanded(
child: Row(
children: [
Expanded(
child: Container(
padding: EdgeInsets.only(
bottom: 10.0
),
margin: EdgeInsets.only(
top: 10.0
),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12.0),
color: inactiveColor
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Text(
"Weight",
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
)
),
SizedBox(
height: 8.0,
),
Text(
weight.toString(),
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
)
),
SizedBox(
height: 8.0,
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
CircleAvatar(
backgroundColor: Colors.blueGrey,
child: IconButton(
icon: Icon(
Icons.add,
color: Colors.white,
),
onPressed: (){
setState(() {
weight++;
});
},
),
),
SizedBox(
width: 10.0
),
CircleAvatar(
backgroundColor: Colors.blueGrey,
child: IconButton(
icon: Icon(
Icons.remove,
color: Colors.white,
),
onPressed: (){
setState(() {
if(weight>10){
weight--;
}
}
);
},
),
),
],
)
],
),
),
),
Expanded(
child: Container(
padding: EdgeInsets.only(
bottom: 10.0
),
margin: EdgeInsets.only(
top: 10.0
),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12.0),
color: selectedGender == Gender.female
? activeColor
: inactiveColor
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Text(
"Age",
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
)
),
SizedBox(
height: 8.0,
),
Text(
age.toString(),
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
)
),
SizedBox(
height: 8.0,
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
CircleAvatar(
backgroundColor: Colors.blueGrey,
child: IconButton(
icon: Icon(
Icons.add,
color: Colors.white,
),
onPressed: (){
setState(() {
age++;
});
},
),
),
SizedBox(
width: 10.0
),
CircleAvatar(
backgroundColor: Colors.blueGrey,
child: IconButton(
icon: Icon(
Icons.remove,
color: Colors.white,
),
onPressed: (){
setState(() {
if(age>5){
age--;
}
}
);
},
),
),
],
)
],
),
),
),
],
),
),
GestureDetector(
child: Container(
padding: EdgeInsets.only(
bottom: 10.0
),
margin: EdgeInsets.only(
top: 10.0
),
width: double.infinity,
height: 80.0,
color: Color(0xFF1DE9B6),
child: Center(
child: Text(
"Calculate BMI",
style: TextStyle(
color: Colors.white,
fontSize: 25.0,
fontWeight: FontWeight.bold,
)
),
),
),
onTap: (){
navigateToResultScreen(12.0);
},
)
],
),
);
}
void navigateToResultScreen(double result){
CalculateResult obj = CalculateResult(weight, height);
Navigator.push(context, MaterialPageRoute(builder: (context) => ResultScreen(obj.calculateResult(),obj.msg, obj.getDescription())));
}
}
除此之外还有另外两个文件：
-
resultscreen.dart：
import 'package:flutter/material.dart'; class ResultScreen extends StatefulWidget { String result; String msg; String des; ResultScreen(this.result, this.msg, this.des); @override _ResultScreenState createState() => _ResultScreenState(); } class _ResultScreenState extends State<ResultScreen> { @override Widget build(BuildContext context) { return Scaffold( backgroundColor: Color(0xFF2F2E3A), appBar: AppBar( title: Text("BMI Results"), ), body: Column( mainAxisAlignment: MainAxisAlignment.center, crossAxisAlignment: CrossAxisAlignment.center, children: [ Expanded( flex: 1, child: Text("Your Results", style: TextStyle( color: Colors.white, fontSize: 25.0, fontWeight: FontWeight.bold, ) ), ), Expanded( flex: 5, child: Container( padding: EdgeInsets.only( bottom: 10.0 ), margin: EdgeInsets.only( top: 10.0 ), decoration: BoxDecoration( borderRadius: BorderRadius.circular(12.0), color: Color(0xFF2F2E3A) ), child: Column( mainAxisAlignment: MainAxisAlignment.spaceEvenly, crossAxisAlignment: CrossAxisAlignment.center, children: [ Text( widget.result, style: TextStyle( color: Colors.green, fontSize: 26.0, ), ), Text( widget.msg, style: TextStyle( fontWeight: FontWeight.bold, color: Colors.green, fontSize: 26.0, ), ), Text( widget.des, style: TextStyle( color: Colors.white, fontSize: 26.0, ), ), Expanded( child: GestureDetector( onTap: (){ Navigator.pop(context); }, child: Container( padding: EdgeInsets.all(10.0), margin: EdgeInsets.only( bottom: 10.0 ), alignment: Alignment.center, color: Color(0xFF1DE9B6), child: Text( "Recalculate...", style: TextStyle( color: Colors.white, fontSize: 25.0, fontWeight: FontWeight.bold, ) ), ), ), ) ], ), ), ) ], ), ); } }- 还有 calresult.dart：
导入“飞镖：数学”；
class CalculateResult{
CalculateResult(this.weight, this.height);
final int height;
final int weight;
double result;
String msg = "Normal";
String calculateResult(){
result = weight / pow(height/100, 2);
return result.toStringAsFixed(1);
}
String getDescription(){
if(result > 25){
msg = "Over weight";
return "You have a higher weight than normal. Try to lose somme through any activity you like!";
}
else if(result > 18.5){
msg = "Normal";
return "You have a normal weight. Keep it!";
}
else if(result < 18.5){
msg = "Under Weight";
return "Your weight is less than normal weight. You need to get some. Make sure to have a correct and balanced diet. ";
}
}
}
希望从社区中获得一些有用的提示来解决这些错误。谢谢！
【问题讨论】：