无法在 flutter 的验证器中获得正确的值

Question

重现步骤

Here is the dartpad link去吧
在字段中输入任何值计算答案。
在任何字段的开头添加 0.

预期结果： 验证者应该 return 0.xyz

实际结果：验证者returns 0xyz

解决方法发现： 使用 onSaved 解决了这个问题

任何人都可以告诉我为什么会发生这种情况或者它是 flutter 中的错误然后我将在 flutter repo 中发布一个新问题

我正在打印来自验证器的值，并在 onChanged 中将字符串值解析为 int。

Answer 1

编辑
当输入 23 然后 inert 0. 时，这一行 amount = int.parse(val); 执行并停止然后点击计算按钮，所以数量是 23 和 value 的 runtimeType 是 String 023

TextFormField(
  keyboardType: TextInputType.number,
  validator: (value) {
    print("amount $amount");
    print(" ${value.runtimeType}");
    print("validator amount value $value ");
    if (value.isEmpty) {
      return "Enter some amount";
    } else if (double.parse(value).toInt() <= 0) {
      return "Amount should be greater than 0";
    }
    return null;
  },
  onChanged: (val){
    print("val1 $val");
    amount = int.parse(val);
    print("amount $amount");
  }

您可以复制粘贴运行下面的完整代码
为什么validator不是return0.xyz
因为 onChanged 在 validator 之前执行
所以 validator 通过 int.parse(value)
接收 t运行的值如果您删除 amount = int.parse(value); 验证器将获得正确的值，但此条件 if (int.parse(value) <= 0) 将得到 Invalid radix-10 number
您需要更改为 if (double.parse(value).toInt() <= 0)

工作演示

完整代码

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.purple,
        buttonTheme: ButtonThemeData(
          buttonColor: Colors.purple.shade400,
        ),
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: BillSpitApp(),
    );
  }
}

class BillSpitApp extends StatefulWidget {
  BillSpitApp({Key key}) : super(key: key);

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

class _BillSpitAppState extends State<BillSpitApp> {
  int amount;
  int numOfPersons;
  double splitAmount;

  GlobalKey<FormState> _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Bill split app"),
      ),
      body: Padding(
        padding: const EdgeInsets.all(15.0),
        child: Form(
          key: _formKey,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                splitAmount == null
                    ? "Fill the details and click on calculate to get your bill split"
                    : "Bill split is ${splitAmount.toStringAsFixed(2)}",
                style: TextStyle(
                  fontSize: 25,
                ),
                textAlign: TextAlign.center,
              ),
              Padding(
                padding: const EdgeInsets.symmetric(vertical: 15.0),
                child: TextFormField(
                  keyboardType: TextInputType.number,
                  validator: (value) {
                    print("validator amount value $value");
                    if (value.isEmpty) {
                      return "Enter some amount";
                    } else if (double.parse(value).toInt() <= 0) {
                      return "Amount should be greater than 0";
                    }
                    return null;
                  },
                  onSaved: (value) {
                    print("onSaved amount value $value");
                    amount = int.parse(value);
                    //int.parse(value);
                  },
                  decoration: InputDecoration(
                    labelText: "Amount",
                    hintText: "1000",
                    border: OutlineInputBorder(),
                  ),
                ),
              ),
              TextFormField(
                validator: (value) {
                  print("person value $value");
                  if (value.isEmpty) {
                    return "Enter number of persons";
                  } else if (double.parse(value).toInt() <= 0) {
                    return "Number should be greater than 0";
                  }
                  return null;
                },
                onSaved: (value) {
                  print("onsave numOfPersons $value");
                  numOfPersons = int.parse(value);
                },
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  labelText: "Number of persons",
                  hintText: "5",
                  border: OutlineInputBorder(),
                ),
              ),
              Padding(
                padding: const EdgeInsets.only(top: 15.0),
                child: RaisedButton(
                  child: Text(
                    "Calculate",
                    style: TextStyle(color: Colors.white),
                  ),
                  onPressed: () {
                    if (_formKey.currentState.validate()) {
                      _formKey.currentState.save();
                      print("calculate $amount");
                      print("calculate $numOfPersons");
                      setState(() {
                        splitAmount = amount / numOfPersons;
                      });
                    }
                  },
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 2

这不是 flutter 的 bug，但是当你将 amount 取为整数时，任何以 0 开头的值，flutter 都会将其视为 0。

if (value.isEmpty) {
   return "Enter some amount";
} else if (double.parse(value) <= 0) {
   return "Amount should be greater than 0";
}
return null;

和

onChanged: (value) {
   amount = double.parse(value);
},

无法在 flutter 的验证器中获得正确的值

Cannot get proper value in validator in flutter

validation

dart

flutter

textformfield

重现步骤