Question

我有100辆卡车的多维阵列。每辆卡车都装有几个箱子。我将每个卡车的第一个盒子从盒阵列拼接到卡车阵列上：

removed = allBoxes.splice(x, 1)[0];
trucks[i] = {0: removed};

因为我知道这是第一个方框，所以我可以放{0:。但是要添加下一个框，我希望它是动态的。我可以在正确的位置插入它，但是下一个框的键是undefined而不是1。

removed = allBoxes.splice(x, 1)[0];
trucks[i][trucks[i].length] = removed;

您可以在这里看到结果：它可以说undefined:而不是1吗？每当我尝试在数组中添加变量时，它只会写出变量字符串，而不是值。

Answer 1

正如@JordanBurnett所提到的，它不是一个数组。我必须计算数组中有多少个对象。使用下面的代码（来自this question）给出了预期的结果：

    import 'package:flutter/material.dart';

class SignupPage extends StatefulWidget {
  @override
  _SignupPageState createState() => _SignupPageState();
}

class _SignupPageState extends State<SignupPage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        resizeToAvoidBottomPadding: false,
        body: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Container(
                child: Stack(
                  children: <Widget>[
                    Container(
                      padding: EdgeInsets.fromLTRB(16.0, 100.0, 0.0, 0.0),
                      child: Text(
                        'Signup',
                        style: TextStyle(
                            fontSize: 80.0, fontWeight: FontWeight.bold),
                      ),
                    ),
                    Container(
                      padding: EdgeInsets.fromLTRB(260.0, 105.0, 0.0, 0.0),
                      child: Text(
                        '.',
                        style: TextStyle(
                            fontSize: 80.0,
                            fontWeight: FontWeight.bold,
                            color: Colors.green),
                      ),
                    )
                  ],
                ),
              ),
              Container(
                  padding: EdgeInsets.only(top: 35.0, left: 20.0, right: 20.0),
                  child: Column(
                    children: <Widget>[
                      TextField(
                        decoration: InputDecoration(
                            labelText: 'Full Name',
                            labelStyle: TextStyle(
                                fontFamily: 'Montserrat',
                                fontWeight: FontWeight.bold,
                                color: Colors.grey),
                            // hintText: 'EMAIL',
                            // hintStyle: ,
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(color: Colors.green))),
                      ),
                      SizedBox(height: 10.0),
                      TextField(
                        decoration: InputDecoration(
                            labelText: 'Email Address ',
                            labelStyle: TextStyle(
                                fontFamily: 'Montserrat',
                                fontWeight: FontWeight.bold,
                                color: Colors.grey),
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(color: Colors.green))),
                        obscureText: true,
                      ),
                      SizedBox(height: 10.0),
                      TextField(
                        decoration: InputDecoration(
                            labelText: 'Confirm Email Address ',
                            labelStyle: TextStyle(
                                fontFamily: 'Montserrat',
                                fontWeight: FontWeight.bold,
                                color: Colors.grey),
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(color: Colors.green))),
                      ),
                      SizedBox(height: 10.0),
                      TextField(
                        decoration: InputDecoration(
                            labelText: 'Password',
                            labelStyle: TextStyle(
                                fontFamily: 'Montserrat',
                                fontWeight: FontWeight.bold,
                                color: Colors.grey),
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(color: Colors.green))),
                        obscureText: true,
                      ),
                      SizedBox(height: 10.0),
                      TextField(
                        decoration: InputDecoration(
                            labelText: 'Phone Number ',
                            labelStyle: TextStyle(
                                fontFamily: 'Montserrat',
                                fontWeight: FontWeight.bold,
                                color: Colors.grey),
                            focusedBorder: UnderlineInputBorder(
                                borderSide: BorderSide(color: Colors.green))),
                        obscureText: true,
                      ),
                      SizedBox(height: 50.0),
                      Container(
                          height: 40.0,
                          child: Material(
                            borderRadius: BorderRadius.circular(20.0),
                            shadowColor: Colors.greenAccent,
                            color: Colors.green,
                            elevation: 7.0,
                            child: GestureDetector(
                              onTap: () {},
                              child: Center(
                                child: Text(
                                  'SIGNUP',
                                  style: TextStyle(
                                      color: Colors.white,
                                      fontWeight: FontWeight.bold,
                                      fontFamily: 'Montserrat'),
                                ),
                              ),
                            ),
                          )),
                      SizedBox(height: 20.0),
                      Container(
                        height: 40.0,
                        color: Colors.transparent,
                        child: Container(
                          decoration: BoxDecoration(
                              border: Border.all(
                                  color: Colors.black,
                                  style: BorderStyle.solid,
                                  width: 1.0),
                              color: Colors.transparent,
                              borderRadius: BorderRadius.circular(20.0)),
                          child: InkWell(
                            onTap: () {
                              Navigator.of(context).pop();
                            },
                            child: Center(
                              child: Text('Go Back',
                                  style: TextStyle(
                                      fontWeight: FontWeight.bold,
                                      fontFamily: 'Montserrat')),
                            ),
                          ),
                        ),
                      ),
                    ],
                  )),
                )
            ]));
  }
}

分配数组值给出未定义的键

1 个答案: