为什么我的 getter 被调用，直到有一个 StackOverflow

Question

我在Winforms应用程序中使用泛型列表，并且在整个过程中都有代码，我将首先检查基础（json）文件是否存在，如果存在，则对其进行反序列化，然后访问反序列化的泛型列表。我决定最好将该代码放在一个地方，因此这样做：

public static List<AssignmentHistory> assignmentHistList
{
    get { return GetAssignmentHistoryList(); }
}
public static List<AssignmentHistory> GetAssignmentHistoryList()
{
    if (!System.IO.File.Exists(ASSIGNMENT_HISTORY_FILENAME)) return null;
    if (null == assignmentHistList)
    {
        return DeserializeAssignmentHistFile();
    }
    return assignmentHistList;
}
public static List<AssignmentHistory> DeserializeAssignmentHistFile()
{
    var assignmentHistFile = System.IO.File.ReadAllText(ASSIGNMENT_HISTORY_FILENAME);
    var assignmentHistDeserialized = JsonConvert.DeserializeObject<List<AssignmentHistory>>(assignmentHist);
    return assignmentHistDeserialized;
}

然后我这样称呼它：

AssignmentHistory ah =
    AYttFMConstsAndUtils.assignmentHistList.FirstOrDefault(
        i => i.WeekOfAssignment == currentWeek && i.TalkType == 1);

。但永远不要超出这一行，因为 GetAssignmentHistoryList（） 会被一遍又一遍地调用，直到出现堆栈溢出。我在这里做错了什么？

更新

我使用了 abto 的空合并运算符建议，但为了防止空文件的可能性，我还必须修改我的反序列化方法，以便现在：

private static List<AssignmentHistory> DeserializeAssignmentHistFile()
{
    List<AssignmentHistory> assignmentHistoryList;
    if (!System.IO.File.Exists(ASSIGNMENT_HISTORY_FILENAME))
    {
        var assignmentFile = System.IO.File.Create(ASSIGNMENT_HISTORY_FILENAME);
        assignmentFile.Close();
    }
    var assignmentHistFile = System.IO.File.ReadAllText(ASSIGNMENT_HISTORY_FILENAME);
    var assignmentHistDeserialized = JsonConvert.DeserializeObject<List<AssignmentHistory>>(assignmentHistFile);
    if (null != assignmentHistDeserialized) return assignmentHistDeserialized;
    assignmentHistoryList = new List<AssignmentHistory>();
    return assignmentHistoryList;
}

Answer 1

因为已经有答案为什么你的代码失败，我想发布一个可能的代码修复：

// this is the backing field for your property
private static List<AssignmentHistory> assignmentHistList;
// it is good practice to name properties starting uppercase
public static List<AssignmentHistory> AssignmentHistList
{
    get 
    {
        // return the content of the backing field if is not null
        return assignmentHistList ??
            // in case the backing field is null,
            // assign it a value from your deserialize method
            // and than return it
            (assignmentHistList = DeserializeAssignmentHistFile());
    }
}
private static List<AssignmentHistory> DeserializeAssignmentHistFile()
{
    // If the file which should contain your data does not exist (yet) return null,
    // the property will retry to set the backing field the next time it is accessed
    if (!System.IO.File.Exists(ASSIGNMENT_HISTORY_FILENAME)) return null;
    var assignmentHistFile 
        = System.IO.File.ReadAllText(ASSIGNMENT_HISTORY_FILENAME);
    var assignmentHistDeserialized 
        = JsonConvert.DeserializeObject<List<AssignmentHistory>>(assignmentHist);
    return assignmentHistDeserialized;
}

然后你可以像你想要的那样（大部分）调用它：

AssignmentHistory ah = AYttFMConstsAndUtils.AssignmentHistList
    .FirstOrDefault(i => i.WeekOfAssignment == currentWeek && i.TalkType == 1);

请记住，如果应从中反序列化的文件不存在，这将引发ArgumentNullException。

Answer 2

Label1:

assignmentHistList属性的 getter 调用GetAssignmentHistoryList()，assignmentHistList属性的 getter 递归调用。

goto Label1;

---

您可能希望使用大写A调用该属性AssignmentHistList，与常见的代码样式做法保持一致，并具有私有静态字段assignmentHistList。无论如何，属性X和GetX()方法存在的双重性是奇怪的。

Answer 3

堆栈溢出异常通常是由于未正确检测到递归调用条件而发生的。

只有观察下面的代码，我们才能推断出存在一个恶性循环调用。

assignmentHistList -> GetAssignmentHistoryList，它检查条件null == assignmentHistList，但为了检查这个条件，它需要再次输入（递归）的assignmentHistList，然后再次调用GetAssignmentHistoryList。你可以看到这是怎么回事。

public static List<AssignmentHistory> assignmentHistList
{
    get { return GetAssignmentHistoryList(); }
}
public static List<AssignmentHistory> GetAssignmentHistoryList()
{
    if (!System.IO.File.Exists(ASSIGNMENT_HISTORY_FILENAME)) return null;
    if (null == assignmentHistList) << Here is another call to the Getter
    // The rest is not important
}