C# foreach循环内调用Append向数组添加对象不生效问题求解

你的代码有3个核心逻辑错误，直接导致元素没有存入数组：

• C#中的数组是固定长度结构，你初始化时写ExerciseAnswer[] exerciseAnswers = new ExerciseAnswer[2]就已经锁定了数组长度，本身不支持动态追加扩容。
• 你调用的Append()是LINQ扩展方法，不会修改原数组，只会返回一个拼接了新元素的全新序列，你没有接收这个返回值，等于这行代码完全没产生实际效果。
• 你用foreach遍历初始全为null的定长数组来赋值的逻辑本身不成立：foreach是用来遍历读取集合元素的，循环中拿到的是数组存储值的拷贝，修改这个拷贝不会影响原数组对应位置的内容。

根据你的需求选一种实现即可：

方案1：固定答案数量时直接用for循环按索引给数组赋值 #

如果提前确定答案总数固定，不需要动态增减，直接用for循环定位到数组索引位赋值，完全不需要调用Append：

static void CreateNewExerciseTest()
{
    string? exerciseName = "Test Exercise";
    string? exerciseTopic = "Test";
    string exerciseQuestion = "Does it work?";
    int numberOfAnswers = 2;
    int numberOfApplicableAnswers = 0;
    ExerciseAnswer[] exerciseAnswers = new ExerciseAnswer[numberOfAnswers];                   

    for (int i = 0; i < exerciseAnswers.Length; i++)
    {
        int exerciseAnswerId = GenerateId();
        Console.WriteLine("\nEnter a name for this Exercise answer: ");
        string? exerciseAnswerName = Console.ReadLine();
        Console.WriteLine("Enter this answer for the Exercise: ");
        string exerciseAnswerContent = Console.ReadLine();
        Console.WriteLine("Enter y (yes) if this Exercise answer is applicable, otherwise press n (no) or any other key: ");
        char applicableAnswer = Console.ReadKey().KeyChar;
        // 吃掉ReadKey遗留的换行符，避免后续ReadLine读入空值
        Console.ReadLine();
        bool applicable = ExerciseAnswer.EvaluateExerciseAnswer(applicableAnswer);
        if (applicable)
        {
            numberOfApplicableAnswers++;
        }

        exerciseAnswers[i] = new ExerciseAnswer(exerciseAnswerId,   
            exerciseAnswerName, exerciseAnswerContent, applicable);
    }
    // 后续构建Exercise对象的逻辑
}

方案2：需要动态调整答案数量时用List代替数组 #

如果后续可能增减答案数量，不要用定长数组，改用支持动态扩容的List<ExerciseAnswer>，调用原生Add方法即可追加元素：

static void CreateNewExerciseTest()
{
    string? exerciseName = "Test Exercise";
    string? exerciseTopic = "Test";
    string exerciseQuestion = "Does it work?";
    int numberOfAnswers = 2;
    int numberOfApplicableAnswers = 0;
    // 初始化动态列表，不需要提前固定长度
    List<ExerciseAnswer> exerciseAnswers = new List<ExerciseAnswer>();                   

    for (int i = 0; i < numberOfAnswers; i++)
    {
        int exerciseAnswerId = GenerateId();
        Console.WriteLine("\nEnter a name for this Exercise answer: ");
        string? exerciseAnswerName = Console.ReadLine();
        Console.WriteLine("Enter this answer for the Exercise: ");
        string exerciseAnswerContent = Console.ReadLine();
        Console.WriteLine("Enter y (yes) if this Exercise answer is applicable, otherwise press n (no) or any other key: ");
        char applicableAnswer = Console.ReadKey().KeyChar;
        Console.ReadLine();
        bool applicable = ExerciseAnswer.EvaluateExerciseAnswer(applicableAnswer);
        if (applicable)
        {
            numberOfApplicableAnswers++;
        }

        ExerciseAnswer exerciseAnswer = new ExerciseAnswer(exerciseAnswerId,   
            exerciseAnswerName, exerciseAnswerContent, applicable);
        // List的Add方法会直接修改原列表，把元素存入集合
        exerciseAnswers.Add(exerciseAnswer);
    }
    // 如果后续逻辑必须接收数组类型，最后调用ToArray转换即可
    // ExerciseAnswer[] finalAnswerArr = exerciseAnswers.ToArray();
}

• 布尔值判断不需要写if (applicable == true)，直接写if (applicable)即可
• 你代码里的numberOfAnswers变量声明后没有实际用到，初始化数组/循环边界直接用这个变量即可，不要硬编码长度2

内容的提问来源于stack exchange，提问作者Daniel