全局变量在计时器tick事件C＃上变为null [英] Global variables are getting null on timer tick event C#

问题描述

亲爱的所有人，



我在ASP.NET C＃中有一个Web应用程序。



目前，我正在努力将QuestionList中的问题显示给候选人。



我创建了一个存储过程来获取一个全局可变的问题列表。< br $>

Dear All,

I have one web application in ASP.NET C#.

Currently, I'm working to display Question from the QuestionList to the candidate.

I have created a stored procedure to get a list of Questions, which is global varaible.

Private List<QuestionInfo> _questionList;

 public List<QuestionInfo> QuestionList
 {
      get
      {
          if(_questionList != null)
             return _questionList;
          else
                 _questionList = 
   QuestionDetailsController.Instance.ExamQuestionsGetRandomly(Module.TotalQuestions, QuestionLanguageID, PracticeModuleID).Select(item => item.Question).ToList();
                return _questionList;
    }
}

我的尝试：

What I have tried:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindQuestion(_questionNumber);
                Timer1.Enabled = true;
            }

        }

protected void BindQuestion(int nthQuestion)
{
    if (nthQuestion <= QuestionList.Count())
    {
        QuestionInfo CurrentQuestion = QuestionList.ElementAt(nthQuestion);
        if (CurrentQuestion != null)
        {
            lblNoOfQuestions.Text = string.Format("Question {0} of {1}", nthQuestion + 1, ExamQuestion.QuestionList.Count());
            lblQuestionText.Text = CurrentQuestion.QuestionDetails.First().Details.Text.QuestionText;
        }
    }
}

我正在使用Ajax UpdatePanel&计时器（显示剩余时间）。



我有三个按钮，如上一个，暂停，下一个。



每当我单击Previous或Next按钮时，全局变量将变为null&在timer_tick事件上也是如此。



如何在单击Next，previous（按钮）或TimerEvent时停止全局变量不得为null。



任何人都可以帮助我。





提前致谢

I'm using Ajax UpdatePanel & Timer(to display time remaining).

I have three buttons, like Previous, Pause, Next.

Whenever I click Previous or Next button, the global variable is getting null & on timer_tick event, as well.

How can I stop global variables not to get null, on clicking the Next, previous(buttons) or TimerEvent.

Can anyone please help me.


Thanks in advance

推荐答案

只有你的控制数据或ViewState中的东西在回发中保持不变，你的本地变量不是每个回发_questionlist都是null，因为你没有在回发时调用BindQuestion。您只需要删除if检查。

Only your control data or things in the ViewState are persisted across postbacks, your local variables are not so on every postback _questionlist will be null as you don't call BindQuestion on postback. You just need to remove the "if" check.

protected void Page_Load(object sender, EventArgs e)
        {
            BindQuestion(_questionNumber);
            if (!IsPostBack)
            {
                Timer1.Enabled = true;
            }
 
        }

你没有显示_questionNumber来自哪里，但是因为我上面说过，如果你想要记住这个值，你需要将它存储在ViewState中，比如

You don't show where _questionNumber comes from, but as I said above if you want that value to be remembered you'll need to store it in the ViewState, something like

<pre>protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                Timer1.Enabled = true;
            }
            else
            {
                _questionNumber = (int)ViewState["questionNumber"];
            }
            BindQuestion(_questionNumber);

            ViewState["questionNumber"] = _questionNumber; 
        }

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