颤振: UnimplementedError，我不明白为什么我会犯这个错误

Question

我真的是新学的代码颤振应用程序(Dart)，我正在遵循一个基本的过程，以建立一个简单的用户界面一步一步。一切都很好，直到我需要创建一个图像滑块(在定制的appBar中)，并且当我创建一个返回一个appBar变量(每个图像的容器)的CardImage类时，Android建议在类中插入一个抛出UnimplementedError()，最后我运行了我的应用程序，它崩溃了，显示了控制台日志中捕获的一个异常。

做了一些谷歌搜索之后，我试图解决这个问题，我不明白为什么当我在throw UnimplementedError()类中注释CardImage时错误消失了，为什么Android建议插入这段代码？有没有更好的解决办法？我会感谢你的帮助。

App误差

我的班级：

import 'package:flutter/material.dart';

class CardImage extends StatelessWidget {
  final String imagePath;

  CardImage(this.imagePath, {Key? key}) : super(key: key) {
    // TODO: implement
    throw UnimplementedError();
  }

  @override
  Widget build(BuildContext context) {
    final card = Container(
      height: 350.0,
      width: 250.0,
      margin: const EdgeInsets.only(
        top: 80.0,
        left: 20.0
      ),
      decoration: BoxDecoration(
        image: DecorationImage(
          fit: BoxFit.cover,
          image: AssetImage(imagePath)
        ),
        borderRadius: const BorderRadius.all(Radius.circular(10.0)),
        shape: BoxShape.rectangle,
        boxShadow: const <BoxShadow>[
          BoxShadow(
            color: Colors.black38,
            // Nivel de degradado
            blurRadius: 15.0,
            // Posición de la sombra (x, y)
            offset: Offset(0.0, 7.0)

          )
        ]
      ),
    );

    return card;
  }
}

控制台日志：

Launching lib\main.dart on sdk gphone x86 in debug mode...
Running Gradle task 'assembleDebug'...
√  Built build\app\outputs\flutter-apk\app-debug.apk.
Installing build\app\outputs\flutter-apk\app.apk...
Debug service listening on ws://127.0.0.1:63533/KSRdMP8cgi0=/ws
Syncing files to device sdk gphone x86...

======== Exception caught by widgets library =======================================================
The following UnimplementedError was thrown building CardImageList(dirty):
UnimplementedError

The relevant error-causing widget was: 
  CardImageList CardImageList:file:///C:/Users/joh4n4lex4nder/Documents/Platzi/Cursos/Flutter/Avanzado/lib/header_app.dart:13:15
When the exception was thrown, this was the stack: 
#0      new CardImage (package:trip_app/card_image.dart:8:5)
#1      CardImageList.build (package:trip_app/card_image_list.dart:18:11)
#2      StatelessElement.build (package:flutter/src/widgets/framework.dart:4827:28)
#3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4754:15)
#4      Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#5      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4735:5)
#6      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4729:5)
#7      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3790:14)
#8      MultiChildRenderObjectElement.inflateWidget (package:flutter/src/widgets/framework.dart:6422:36)
#9      MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6433:32)
...     Normal element mounting (7 frames)
#16     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3790:14)
#17     MultiChildRenderObjectElement.inflateWidget (package:flutter/src/widgets/framework.dart:6422:36)
#18     MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6433:32)
...     Normal element mounting (19 frames)
#37     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3790:14)
#38     MultiChildRenderObjectElement.inflateWidget (package:flutter/src/widgets/framework.dart:6422:36)
#39     MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6433:32)
...     Normal element mounting (255 frames)
#294    Element.inflateWidget (package:flutter/src/widgets/framework.dart:3790:14)
#295    MultiChildRenderObjectElement.inflateWidget (package:flutter/src/widgets/framework.dart:6422:36)
#296    MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6433:32)
...     Normal element mounting (377 frames)
#673    Element.inflateWidget (package:flutter/src/widgets/framework.dart:3790:14)
#674    Element.updateChild (package:flutter/src/widgets/framework.dart:3540:18)
#675    RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1198:16)
#676    RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:1167:5)
#677    RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:1112:18)
#678    BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2600:19)
#679    RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:1111:13)
#680    WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:944:7)
#681    WidgetsBinding.scheduleAttachRootWidget.<anonymous closure> (package:flutter/src/widgets/binding.dart:924:7)
(elided 11 frames from class _RawReceivePortImpl, class _Timer, dart:async, and dart:async-patch)
====================================================================================================
I/OpenGLRenderer( 1507): Davey! duration=725ms; Flags=0, IntendedVsync=159868971593464, Vsync=159868971593464, OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=159868980901800, AnimationStart=159868980931200, PerformTraversalsStart=159868980972100, DrawStart=159868982275600, SyncQueued=159869022993700, SyncStart=159869028916400, IssueDrawCommandsStart=159869072195400, SwapBuffers=159869684501800, FrameCompleted=159869703161500, DequeueBufferDuration=7169100, QueueBufferDuration=715000, GpuCompleted=72904454231491230, 

Answer 1

“此错误由未完成的代码引发，该代码尚未实现所需的所有功能。

如果类不打算实现该特性，则应该抛出一个UnsupportedError。此错误仅供开发期间使用。“

如果你有更多的兴趣到这里去，https://api.flutter.dev/flutter/dart-core/UnimplementedError-class.html

我相信有些人会使用它作为临时占位符，这样当他们到达代码的那一部分时，你会得到一个错误，提醒他们他们仍然必须完成/实现代码的那一部分。

希望这能有所帮助

Answer 2

在您的代码(第6行)中，我看到它显式地抛出了前面提到的错误，请您删除这一行，然后再试一次。

Answer 3

请删除CardImage构造函数中的“抛出CardImage()”，例如：

const CardImage(this.imagePath, {Key? key}) : super(key: key);

在某些语言中，它充当REMIDER，它防止开发人员忘记实现函数，您可以在kotlin等语言中找到类似的情况。