Question

我有以下返回空值的方法，尝试对其进行调试，我发现到达最后一行（返回值）时，要返回的变量具有预期值，但没有退出该方法并返回值，代码会使用“ NullReferenceException”返回到前面的捕获中，并在此之后返回null。仅当在多个线程中同时调用该方法时，这种情况才会发生。
有人可以向我解释为什么会这样吗？

调用块：

List<Thread> threads = new List<Thread>();
foreach (Event eV in temp)
{
    var associatedUserEvent = new User_Event().GetItemByFilter("Event", eV.Title);
    ThreadStart c = new ThreadStart(() => xx(temp2, eV));
    Thread cT = new Thread(c);
    threads.Add(cT);
    cT.Start();
}
foreach (var cT in threads)
{
    cT.Join();
}

调用方法：

public void xx(List<User_Event> temp2, Event eV)
        {
            var associatedUserEvent = new User_Event().GetItemByFilter("Event", eV.Title);
            if (associatedUserEvent != null) temp2.Add(associatedUserEvent);
        }

向后运行的

方法：（字符串a，c和t仅用于调试目的）

public SPListItemCollection executeQuery()
    {

        SPListItemCollection toReturn = null;
        string a, t, c;

        try
        {
            SPWeb web = SPContext.Current.Web;

            SPSecurity.RunWithElevatedPrivileges(delegate()
            {
                if (type.getListName() != null)
                {
                    SPList list = web.GetList(web.ServerRelativeUrl + "/Lists/" + type.getListName());

                    if (filters != null || folderPath != null)
                    {

                        SPQuery query = new SPQuery();

                        if (customViewFields != null)
                        {
                            query.ViewFields = buildViewFields();
                            query.ViewFieldsOnly = true;
                            query.IncludeMandatoryColumns = false;
                        }

                        query.IncludeAttachmentUrls = true;
                        query.Folder = web.GetFolder(web.ServerRelativeUrl + "/Lists/" + type.getListName() + "/" + folderPath);
                        query.Query = this.filters != null && this.filters.Length > 0 ? this.CreateCAMLQuery() : @"<Query><OrderBy><FieldRef Name='ID' /></OrderBy></Query>";
                        query.ViewAttributes = "Scope=\"Recursive\"";
                        toReturn = list.GetItems(query);
                        a = "";
                    }
                    else
                    {
                        toReturn = list.GetItems(customViewFields);
                    }
                    c = "";
                }
                else
                {
                    throw new System.ArgumentException("Custom attributte listname cannot be null");
                }

                t = "";
            });
        }
        catch (Exception exception)
        {
            a = "";
        }

        return toReturn;
    }

如何返回方法的值？

0 个答案: