我有三个文本字段，想在前两个之间进行选择，然后使用第三个

Question

我有三个文本字段。我想在前两个中选择一个，然后与第三个一起使用。

怎么做？请指导

import 'package:flutter/material.dart';

void main() => runApp(new CalculatorApp());

class CalculatorApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(title:'Bending Calculator',
      home: Calculator()
    );
  }
}

class Calculator extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => Calculatore();
}

class Calculatore extends State<Calculator> {
final a = TextEditingController();
  final b = TextEditingController();
  final c = TextEditingController();
// controller mentioned
 String total= "";

void calculate()  {
    int numberA = int.parse(a.text);
    int numberB = int.parse(b.text);
    int numberC = int.parse(c.text);
    int  result;
// if numberA have value then answer will be a+c


if( 
// what condition to do here for between choosing between  textfields a or b.
// i tried numberB ==null   that does not work
// very much confused, no idea what to do please help

){
result = numberA + numberC
} else{ result = numberB + numberC
}


    setState(() {
      total = "$result";
    });
  }
  @override
  Widget build(BuildContext context) {
return Scaffold(appBar: AppBar(title:Text("Calculator")),
        body: SafeArea(
            child: ListView(
              children: <Widget>[
                Row( mainAxisAlignment: MainAxisAlignment.center ,
                  children: <Widget>[
                    // first textfield

                    Container(width: MediaQuery.of(context).size.width *0.45 ,height: 50,
                       child: TextField(
                           controller: a,
                           decoration: InputDecoration(hintText: " Enter a value"),
                           keyboardType: TextInputType.number),
                    ),
                    Container(width: MediaQuery.of(context).size.width * 0.04,height: 50,),
                    // second textfield
                    Container(width: MediaQuery.of(context).size.width* 0.45,height: 50,
                      child: TextField(
                          controller: b,
                          decoration: InputDecoration(hintText: " Enter  b value"),
                          keyboardType: TextInputType.number),), ],
                ),
               
                Row(mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[

                    // third textfield

                    Container(width: MediaQuery.of(context).size.width *0.9, height: 50,
                      child: TextField(
                          controller: c,
                          decoration: InputDecoration(hintText: "   Enter c value"),
                          keyboardType: TextInputType.number),),
                  ],
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[

                    //button

                    RaisedButton(
                      onPressed: calculate,
                      child: Text('Calculate'),),
                  ],
                ),
                Text("   Total : $total", style: TextStyle(fontSize: 20.0),),
      ],
            ))
    );
  }
}

Answer 1

据我了解，您已尝试检查文本字段 b 的值是否为空。您是否尝试检查 b.text.isEmpty 或 isNotEmpty.

Answer 2

根据您的评论，这可能会有所帮助。如果您提供的要解析的文本为空，则正常的 int.parse 将抛出错误。而是像文档 here. This will return a null if the provided string is empty. Live version available in this dartpad.

中那样使用 int.tryParse

    int numberA = int.tryParse(a.text);
    int numberB = int.tryParse(b.text);
    int numberC = int.tryParse(c.text);
    int result;

    // if numberA have value then answer will be a+c

    // Note following conditions have order precedence. So only one of them execute.     
    if (numberA != null && numberC != null) {
      result = numberA + numberC;
    } else if (numberB != null && numberC != null){
      result = numberB + numberC;
    }

如果三个字段都存在，你想计算总计。使用以下条件。

    if (numberA != null && numberB != null && numberC != null) {
      result = numberA + numberB + numberC;
    } else if (numberA != null && numberC != null) {
      result = numberA + numberC;
    } else if (numberB != null && numberC != null){
      result = numberB + numberC;
    }

您可以通过检查文本而不是解析的数字来实现相同的目的。

Answer 3

"" 无法解析为 int。您可以使用 "try & catch" 或 "tryParese"。这个怎么样？

void calculate() {
  int numberA = int.tryParse(a.text);
  int numberB = int.tryParse(b.text);
  int numberC = int.tryParse(c.text);
  int result;

  if (numberB == null) {
    result = numberA + numberC;
  } else {
    result = numberB + numberC;
  }

  setState(() {
    total = "$result";
  });
}

我有三个文本字段，想在前两个之间进行选择，然后使用第三个

I have three text fields, want to choose between first two of them, & work with third one

textfield

dart

flutter