Flutter 中的 AlertDialog 小部件无法使用 setState 功能答案

【问题标题】：AlertDialog widget not working setState function in FlutterFlutter 中的 AlertDialog 小部件无法使用 setState 功能
【发布时间】：2020-09-26 00:16:46
【问题描述】：

我开始使用 DropdownButton 小部件并创建了城市列表。
当我在列表中选择我最喜欢的城市时，我想看到 AlertDialog，但它无法工作。这是代码：

import 'package:flutter/material.dart';
import './func.dart';
class ChooseCity extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return ChooseCityState();
  }
}

class ChooseCityState extends State<ChooseCity> {
  var cities = ["Ankara", "İzmir", "İstanbul", "Edirne", "Antalya"];
  String choosenCity = "Edirne";

  @override
  Widget build(BuildContext context) {
    return Column(

      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[



        DropdownButton<String>(
          items: cities.map((String city) {
            return DropdownMenuItem<String>(
              child: Text(city),
              value: city,
            ); 
          }).toList(),
          value: choosenCity,
          onChanged: (String choosen) {

            setState(() {
          choosenCity = choosen;});
          choosen=="Antalya" ? 
            AlertDialog(
              title:Text("ATTENTION"),
              content: Text("You chose the best place!!"),
              actions: [
                 FlatButton(child: Text("I see,I agree"),onPressed: ()=>{},)
                   ],


                )

              : Text("go on");

          },


        ),
        SizedBox(
          height: 60,
        ),
        Text(
          "    You choosed  :" + choosenCity,
          textAlign: TextAlign.center,


        ),
      ],
    );

  }
}

查看我的页面：

它看起来不像我想要的。当我选择 "Antalya" 时，我想看到 AlertDialog。错误在哪里？我应该把布尔函数放在哪里？我试图把这个 bool 函数从 setState 函数中去掉，但它不是我想要的。

【问题讨论】：

标签： android-studio flutter visual-studio-code widget setstate

【解决方案1】：

如果您想显示警报对话框，您应该使用“showDialog”，然后在其构建器中使用您的警报对话框。

这样

class ChooseCity extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return ChooseCityState();
  }
}

class ChooseCityState extends State<ChooseCity> {
  var cities = ["Ankara", "İzmir", "İstanbul", "Edirne", "Antalya"];
  String chosenCity = "Edirne";

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        DropdownButton<String>(
          items: cities.map((String city) {
            return DropdownMenuItem<String>(
              child: Text(city),
              value: city,
            );
          }).toList(),
          value: chosenCity,
          onChanged: (String choosen) {
            chosenCity = choosen;
            showAlertDialog();
            setState(() {});
          },
        ),
        SizedBox(
          height: 60,
        ),
        Text(
          "    You choosed  :" + chosenCity,
          textAlign: TextAlign.center,
        ),
      ],
    );
  }

  showAlertDialog() {
    showDialog(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: Text("ATTENTION"),
          content: Text("You chose the best place!!"),
          actions: [
            FlatButton(
              child: Text("I see,I agree"),
              onPressed: () => {},
            )
          ],
        );
      },
    );
  }
}

【讨论】：

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