dart - 如何在 onTap 中使用条件语句

Question

我对 dart 中的 if 语句有疑问，我希望用户点击城市转到新屏幕。这段代码工作得很好

class citySec extends StatelessWidget {
  Widget getListView(BuildContext context) {
    var listView = ListView(
      children: <Widget>[
        Text(
          "choose ur city:",
          textDirection: TextDirection.rtl,
          textAlign: TextAlign.center,
        ),
        ListTile(
          leading: Icon(Icons.location_city),
          title: Text("Toronto ", textDirection: TextDirection.rtl),

          onTap: () {
            Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => TorontoUniversitySection(),
              ),
            );
          },
        ),
      ],
    );
    return listView;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(body: getListView(context));
  }
}

由于我有很长的城市列表，而以前的代码会使我的代码很长，所以我不得不更改我的代码。但是，我在 if 语句中遇到了一些错误，这是我目前所做的。

import 'package:flutter/material.dart';
import 'package:rate/screens/firstScreen.dart';

void main() {
  runApp(MaterialApp(
    debugShowCheckedModeBanner: false,
    title: 'Rate',
    home: Scaffold(
      appBar: AppBar(
        title: Text("jgfnjfnj ", textDirection: TextDirection.rtl),
      ),
      body: ListDisplay(),
    ),
  ));
}
class ListDisplay extends StatelessWidget {
  List<String> litems = ["Toronto","NewYork","London","Riyadh","Dubai","Istanbul"];

  @override
  Widget build (BuildContext ctxt) {
    return new Scaffold(
      appBar: AppBar(title: Text("Please Choose your city: ", textDirection: TextDirection.ltr,),
      ),

    body: new ListView.builder
    (
    itemCount: litems.length,

    itemBuilder: (BuildContext ctxt, int index) {

    return new ListTile(
      leading: Icon(Icons.location_city),
      title: Text(litems[index], textDirection: TextDirection.rtl),

      onTap: () {
// begin of all IF statements

        if (litems.contains("Totonto")){
          Navigator.push(
            ctxt,
            MaterialPageRoute(

              builder: (ctxt) => TorontoUniversitySection()
            ),
          );

        }
if (litems.contains("London")){
          Navigator.push(
            ctxt,
            MaterialPageRoute(

              builder: (ctxt) => LondonUniversitySection()
            ),
          );

        }

// end of all If statements

      },
    );

    }
    )
    );
  }
}

Answer 1

for example, when I press Toronto it will take me to LondonUniversitySection()

那是因为在您的 if 语句中，您检查您的列表是否包含 Toronto/London 而不是当前按下的是 Toronto/London。将 litems.contains("x") 更改为 litems[index] == "x" 即可。这是经过编辑的片段:

    return new ListTile(
      leading: Icon(Icons.location_city),
      title: Text(litems[index], textDirection: TextDirection.rtl),
      onTap: () {
        if (litems[index] == "Toronto") {
          Navigator.push(
            ctxt,
            MaterialPageRoute(builder: (ctxt) => TorontoUniversitySection()),
          );
        } else if (litems[index] == "London") {
          Navigator.push(
            ctxt,
            MaterialPageRoute(builder: (ctxt) => LondonUniversitySection()));
        }
      },
    );

此外，我建议为此使用 switch 或 else-if，而不是一堆 ifs。