c# - 无法将类型 'System.Action'隐式转换为 'mathstester.Program.OperationQuestionScore'

Question

我做了一个C#控制台数学项目，用户可以根据他们选择的难度回答加，减，乘，除，幂或平方根问题!

这是我的完整代码:

using System;
using System.Collections.Generic;
using System.Linq;

namespace mathstester
{
    class Program
    {
        public enum UserDifficulty
        {
            Easy,
            Normal,
            Hard
        }

        public enum MathOperation
        {
            Addition = 1,
            Subtraction = 2,
            Multiplication = 3,
            Division = 4,
            Power = 5,
            SquareRoot = 6
        }
        public static (int operationMin, int operationMax) GetPossibleOperationsByDifficulty(UserDifficulty userDifficulty)
        {

            switch (userDifficulty)
            {
                case UserDifficulty.Easy:
                    return (1, 4);
                case UserDifficulty.Normal:
                    return (1, 5);
                case UserDifficulty.Hard:
                    return (3, 7);
                default:
                    throw new Exception();
            }
        }

        public class OperationQuestionScore
        {
            public int AdditionQuestion { get; set; }
            public int AdditionScore { get; set; }
            public int SubtractionQuestion { get; set; }
            public int SubtractionScore { get; set; }
            public int MultiplicationQuestion { get; set; }
            public int MultiplicationScore { get; set; }
            public int DivisionQuestion { get; set; }
            public int DivisionScore { get; set; }
            public int PowerQuestion { get; set; }
            public int PowerScore { get; set; }
            public int SquareRootQuestion { get; set; }
            public int SquareRootScore { get; set; }

            public static (OperationQuestionScore, OperationQuestionScore) Scores(MathOperation mathOperation)
            {
                Action<OperationQuestionScore> incrementOperationQuestion;
                Action<OperationQuestionScore> incrementOperationScore;
                switch (mathOperation)
                {
                    case MathOperation.Addition:
                        incrementOperationQuestion = incrementquestion => incrementquestion.AdditionQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.AdditionScore++;
                    case MathOperation.Subtraction:
                        incrementOperationQuestion = incrementquestion => incrementquestion.SubtractionQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.SubtractionScore++;
                        break;
                    case MathOperation.Multiplication:
                        incrementOperationQuestion = incrementquestion => incrementquestion.MultiplicationQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.MultiplicationScore++;
                        break;
                    case MathOperation.Division:
                        incrementOperationQuestion = incrementquestion => incrementquestion.DivisionQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.DivisionScore++;
                        break;
                    case MathOperation.Power:
                        incrementOperationQuestion = incrementquestion => incrementquestion.PowerQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.PowerScore++;
                        break;
                    case MathOperation.SquareRoot:
                        incrementOperationQuestion = incrementquestion => incrementquestion.SquareRootQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.SquareRootScore++;
                        break;
                    default:
                        break;
                }
                return (incrementOperationQuestion, incrementOperationScore);
            }
        }

        public static OperationQuestionScore Score()
        {
            return new OperationQuestionScore();
        }

        public static (string message, double correctAnswer) GetMathsEquation(MathOperation mathOperation, UserDifficulty userDifficulty)
        {
            int number1;
            int number2;
            Random randomNumber = new Random();

            switch (mathOperation)
            {
                case MathOperation.Addition:
                    number1 = randomNumber.Next(1000);
                    number2 = randomNumber.Next(1000);
                    return ($"{number1} + {number2}", number1 + number2);
                case MathOperation.Subtraction:
                    number1 = randomNumber.Next(1000);
                    number2 = randomNumber.Next(1000);
                    return ($"{number1} - {number2}", number1 - number2);
                case MathOperation.Multiplication:
                    number1 = userDifficulty == UserDifficulty.Easy ? randomNumber.Next(13) : randomNumber.Next(1000);
                    number2 = userDifficulty == UserDifficulty.Easy ? randomNumber.Next(13) : randomNumber.Next(1000);
                    return ($"{number1} * {number2}", number1 * number2);
                case MathOperation.Division:
                    number1 = randomNumber.Next(10000);
                    number2 = randomNumber.Next(1000);
                    return ($"{number1} / {number2}", number1 / (double)number2);
                case MathOperation.Power:
                    number1 = randomNumber.Next(13);
                    number2 = randomNumber.Next(5);
                    return ($"{number1} ^ {number2}", Math.Pow(number1, number2));
                case MathOperation.SquareRoot:
                    number1 = randomNumber.Next(1000);
                    return ($"√{number1}", Math.Sqrt(number1));
                default:
                    throw new Exception();
            }
        }

        public static (int, OperationQuestionScore, OperationQuestionScore) RunTest(int numberOfQuestionsLeft, UserDifficulty userDifficulty)
        {
            int totalScore = 0;
            Random random = new Random();
            var (operationMin, operationMax) = GetPossibleOperationsByDifficulty(userDifficulty);
            var score = Score();
            var question = Score();
            var (incrementOperationQuestion, incrementOperationScore) = Scores();
            while (numberOfQuestionsLeft > 0)
            {
                int mathRandomOperation = random.Next(operationMin, operationMax);
                MathOperation mathOperation = (MathOperation)mathRandomOperation;
                var (message, correctAnswer) = GetMathsEquation(mathOperation, userDifficulty);
                if (mathRandomOperation == 4 || mathRandomOperation == 6)
                {
                    Console.Write($"To the nearest integer, What is {message} =");
                }
                else
                {
                    Console.Write($"What is {message} =");
                }
                double userAnswer = Convert.ToDouble(Console.ReadLine());
                if (Math.Round(correctAnswer) == userAnswer)
                {
                    Console.WriteLine("Well Done!");
                    incrementOperationQuestion(question);
                    incrementOperationScore(score);
                    totalScore++;
                }
                else
                {
                    Console.WriteLine("Your answer is incorrect!");
                    incrementOperationQuestion(question);
                }
                numberOfQuestionsLeft--;
            }
            return (totalScore, score, question);
        }
        public static void Main(string[] args)
        {
            Dictionary<string, UserDifficulty> difficultyDictionary = new Dictionary<string, UserDifficulty>();
            difficultyDictionary.Add("E", UserDifficulty.Easy);
            difficultyDictionary.Add("N", UserDifficulty.Normal);
            difficultyDictionary.Add("H", UserDifficulty.Hard);

            string userInputDifficulty = "";
            do
            {
                Console.WriteLine("What difficulty level would you like to do! Please type E for Easy, N for Normal and H for hard");
                userInputDifficulty = Console.ReadLine().ToUpper();
            } while (userInputDifficulty != "E" && userInputDifficulty != "N" && userInputDifficulty != "H");

            UserDifficulty userDifficulty = difficultyDictionary[userInputDifficulty];

            int numberOfQuestions = 0;
            do
            {
                Console.WriteLine("How many questions would you like to answer? Please type a number divisible by 10!");
                int.TryParse(Console.ReadLine(), out numberOfQuestions);
            } while (numberOfQuestions % 10 != 0);

            var (totalScore, score, question) = RunTest(numberOfQuestions, userDifficulty);
            Console.WriteLine($"Total score: {totalScore} of {numberOfQuestions}");

            if (userDifficulty == UserDifficulty.Easy)
            {
                Console.WriteLine($"Addition score: {score.AdditionScore} of {question.AdditionQuestion}");
                Console.WriteLine($"Subtraction score: {score.SubtractionScore} of {question.SubtractionQuestion}");
                Console.WriteLine($"Multiplication score: {score.MultiplicationScore} of {question.MultiplicationQuestion}");
            }
            else if (userDifficulty == UserDifficulty.Normal)
            {
                Console.WriteLine($"Addition score: {score.AdditionScore} of {question.AdditionQuestion}");
                Console.WriteLine($"Subtraction score: {score.SubtractionScore} of {question.SubtractionQuestion}");
                Console.WriteLine($"Multiplication score: {score.MultiplicationScore} of {question.MultiplicationQuestion}");
                Console.WriteLine($"Division score: {score.DivisionScore} of {question.DivisionQuestion}");
            }
            else if (userDifficulty == UserDifficulty.Hard)
            {
                Console.WriteLine($"Multipication score: {score.MultiplicationScore} of {question.MultiplicationQuestion}");
                Console.WriteLine($"Division score: {score.DivisionScore} of {question.DivisionQuestion}");
                Console.WriteLine($"Power score: {score.PowerScore} of {question.PowerQuestion}");
                Console.WriteLine($"Squareroot score: {score.SquareRootScore} of {question.SquareRootQuestion}");
            }
        }
    }
}

这是我的问题所在:

public static (OperationQuestionScore, OperationQuestionScore) Scores(MathOperation mathOperation)
            {
                Action<OperationQuestionScore> incrementOperationQuestion;
                Action<OperationQuestionScore> incrementOperationScore;
                switch (mathOperation)
                {
                    case MathOperation.Addition:
                        incrementOperationQuestion = incrementquestion => incrementquestion.AdditionQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.AdditionScore++;
                    case MathOperation.Subtraction:
                        incrementOperationQuestion = incrementquestion => incrementquestion.SubtractionQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.SubtractionScore++;
                        break;
                    case MathOperation.Multiplication:
                        incrementOperationQuestion = incrementquestion => incrementquestion.MultiplicationQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.MultiplicationScore++;
                        break;
                    case MathOperation.Division:
                        incrementOperationQuestion = incrementquestion => incrementquestion.DivisionQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.DivisionScore++;
                        break;
                    case MathOperation.Power:
                        incrementOperationQuestion = incrementquestion => incrementquestion.PowerQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.PowerScore++;
                        break;
                    case MathOperation.SquareRoot:
                        incrementOperationQuestion = incrementquestion => incrementquestion.SquareRootQuestion++;
                        incrementOperationScore = incrementscore => incrementscore.SquareRootScore++;
                        break;
                    default:
                        break;
                }
                return (incrementOperationQuestion, incrementOperationScore);
            }

在我的函数“Score”中， return (incrementOperationQuestion, incrementOperationScore);出错。

错误说

1. Cannot implicitly convert type 'System.Action<mathstester.Program.OperationQuestionScore>'
    to 'mathstester.Program.OperationQuestionScore'

2. Use of unassigned local variable 'incerementOperationScore'

我该如何解决？

Answer 1

Cannot implicitly convert type 'System.Action' to 'mathstester.Program.OperationQuestionScore'

发生此错误是因为方法 Scores被声明为返回 (OperationQuestionScore, OperationQuestionScore)类型的元组，但实际上它返回了 (Action<OperationQuestionScore>, Action<OperationQuestionScore>)类型的元组。要解决此问题，您应该更改 Scores方法的返回类型:

public static (Action<OperationQuestionScore>, Action<OperationQuestionScore>) Scores(MathOperation mathOperation)

Use of unassigned local variable 'incerementOperationScore'

该错误表明存在未分配给值的变量的用法。在您的情况下，编译器告诉您可以使用未分配的变量 incerementOperationScore。如果参数 mathOperation与任何切换用例都不匹配，并且空的 default用例未将值分配给 incerementOperationScore，则会发生这种情况。目前，所有可能的 mathOperation值都由switch语句处理，这意味着 default分支将永远不会执行。但是将来您可能会添加新的数学运算，而忘记将其添加到此switch语句中。为了防止此类错误，编译器迫使我们处理所有可能的case值(即使将来会添加它们)。

要解决此问题，您应该在 default情况下抛出异常:

default:
    throw new System.ComponentModel.InvalidEnumArgumentException("mathOperation", (int) mathOperation, typeof(MathOperation));

或处理 MathOperation情况下的 default值之一:

default: // For example, use default branch instead of MathOperation.SquareRoot branch.
    incrementOperationQuestion = incrementquestion => incrementquestion.SquareRootQuestion++;
    incrementOperationScore = incrementscore => incrementscore.SquareRootScore++;
    break;

我个人比较喜欢抛出一个异常。当您忘记为新添加的枚举值添加新的case分支时，它有助于处理情况。
Scores方法中还有另一个错误。在第一个case分支中缺少 break关键字。

这是带有固定错误的完整 Scores方法:

public static (Action<OperationQuestionScore>, Action<OperationQuestionScore>) Scores(MathOperation mathOperation)
{
    Action<OperationQuestionScore> incrementOperationQuestion;
    Action<OperationQuestionScore> incrementOperationScore;
    switch (mathOperation)
    {
       case MathOperation.Addition:
          incrementOperationQuestion = incrementquestion => incrementquestion.AdditionQuestion++;
          incrementOperationScore = incrementscore => incrementscore.AdditionScore++;
          break;
       case MathOperation.Subtraction:
          incrementOperationQuestion = incrementquestion => incrementquestion.SubtractionQuestion++;
          incrementOperationScore = incrementscore => incrementscore.SubtractionScore++;
          break;
       case MathOperation.Multiplication:
          incrementOperationQuestion = incrementquestion => incrementquestion.MultiplicationQuestion++;
          incrementOperationScore = incrementscore => incrementscore.MultiplicationScore++;
          break;
       case MathOperation.Division:
          incrementOperationQuestion = incrementquestion => incrementquestion.DivisionQuestion++;
          incrementOperationScore = incrementscore => incrementscore.DivisionScore++;
          break;
       case MathOperation.Power:
          incrementOperationQuestion = incrementquestion => incrementquestion.PowerQuestion++;
          incrementOperationScore = incrementscore => incrementscore.PowerScore++;
          break;
       case MathOperation.SquareRoot:
          incrementOperationQuestion = incrementquestion => incrementquestion.SquareRootQuestion++;
          incrementOperationScore = incrementscore => incrementscore.SquareRootScore++;
          break;
       default:
          throw new InvalidEnumArgumentException("mathOperation", (int) mathOperation, typeof(MathOperation));
    }
    return (incrementOperationQuestion, incrementOperationScore);
}

@ crazydanyal1414在评论中问:

But how would I define the "Scores" function into "RunTest"?

需要对方法 RunTest进行较小的更改。这是更改的方法 RunTest。我描述了注释中的更改:

public static (int, OperationQuestionScore, OperationQuestionScore) RunTest(int numberOfQuestionsLeft, UserDifficulty userDifficulty)
{
    int totalScore = 0;
    Random random = new Random();
    var (operationMin, operationMax) = GetPossibleOperationsByDifficulty(userDifficulty);
    var score = Score();
    var question = Score();

    // Move this line into the while loop.
    //var (incrementOperationQuestion, incrementOperationScore) = Scores();

    while (numberOfQuestionsLeft > 0)
    {
        int mathRandomOperation = random.Next(operationMin, operationMax);
        MathOperation mathOperation = (MathOperation)mathRandomOperation;
        var (message, correctAnswer) = GetMathsEquation(mathOperation, userDifficulty);
        if (mathRandomOperation == 4 || mathRandomOperation == 6)
        {
           Console.Write($"To the nearest integer, What is {message} =");
        }
        else
        {
           Console.Write($"What is {message} =");
        }

        // Here is moved line.
        // Method Scores must be invoked using static method invocation
        // syntax, and a parameter mathOperation must be passed into it.
        var (incrementOperationQuestion, incrementOperationScore) = OperationQuestionScore.Scores(mathOperation);

        double userAnswer = Convert.ToDouble(Console.ReadLine());
        if (Math.Round(correctAnswer) == userAnswer)
        {
           Console.WriteLine("Well Done!");
           incrementOperationQuestion(question);
           incrementOperationScore(score);
           totalScore++;
        }
        else
        {
           Console.WriteLine("Your answer is incorrect!");
           incrementOperationQuestion(question);
        }
        numberOfQuestionsLeft--;
     }
     return (totalScore, score, question);
}