validation - 在Flutter中无法在验证器中获得适当的值

Question

重现步骤

Here is the dartpad link转到它。

在字段中输入任何值以计算答案。

将0添加到任何字段

的开头

预期结果:验证程序应返回0.xyz
实际结果:验证程序返回0xyz
解决方法:使用onSaved的解决了此问题
谁能告诉我为什么会这样或它是否会在Flutter中出错，那么我将在Flutter Repo中发布一个新问题

我正在打印来自验证程序的值，并在将字符串值转换为int的onChanged中进行打印。

Answer 1

编辑
当输入23，然后输入惰性0.时，此行amount = int.parse(val);执行并停止，然后单击“计算”按钮，因此数量为23，而value的runtimeType为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");
  }

您可以在下面复制粘贴运行完整代码 validator不返回 0.xyz的原因
因为 onChanged在 validator之前执行
因此， validator通过 int.parse(value)接收截断的值
如果删除 amount = int.parse(value);，验证程序将获得正确的值，但是
此条件 if (int.parse(value) <= 0)将获得 Invalid radix-10 number您需要更改为 if (double.parse(value).toInt() <= 0)工作演示

完整的代码

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;
                      });
                    }
                  },
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}