An exception of type 'System.NullReferenceException' : Object reference not set to an instance of an object

Question

So I am really confused. I have some code:

public ActionResult submitSurveyQuestion(SurveyQuestion model) 
    {
        SurveyQuestion nextQuestion = new SurveyQuestion();
        nextQuestion = submitSurveyQuestionAndGetNextQuestionFromQuestion(model);
        return RedirectToAction("generateViewForSurveyQuestion", new { question = nextQuestion });
    }

public SurveyQuestion submitSurveyQuestionAndGetNextQuestionFromQuestion(SurveyQuestion currentQuestion)
    {
        SurveyQuestion surveyQuestion = new SurveyQuestion();
        surveyQuestion.Question = "question";
        //...etc, this just sets all the question properties
        return surveyQuestion;
    }
public ActionResult generateViewForSurveyQuestion(SurveyQuestion question)
    {
        //ERROR BELOW THIS LINE
        return View("SurveyQuestionType" + question.QuestionType, question);
        //ERROR ABOVE THIS LINE
    }

But for some reason, my code returns the error:An exception of type 'System.NullReferenceException' : Object reference not set to an instance of an object. When looking through the debugger, it says that question = null, but I set all the properties of question and instantiate it, so I am really confused as to what's going wrong here.....any guidance would be greatly appreciated.

in what line do you get the error? return View("SurveyQuestionType" + question.QuestionType, question); here? — DanielVorph
– DanielVorph, Commented Jul 27, 2015 at 23:23
You're using a RedirectToAction to hit the controller method. That sends a 302 response to the browser which then sends a request back to your controller. The nextQuestion object you created in submitSurveyQuestion is long gone by that point. — Craig W.
– Craig W., Commented Jul 27, 2015 at 23:29
possible duplicate of What is a NullReferenceException and how do I fix it? — Craig W.
– Craig W., Commented Jul 27, 2015 at 23:30
No, it need not be one method, you just should not use RedirectToAction() in this context. — Peter Gluck
– Peter Gluck, Commented Jul 27, 2015 at 23:46

Peter Gluck · Accepted Answer · 2015-07-27 23:39:12Z

4

You should call generateViewForSurveyQuestion() directly to return the view:

public ActionResult submitSurveyQuestion(SurveyQuestion model) {
  SurveyQuestion nextQuestion = new SurveyQuestion();
  nextQuestion = submitSurveyQuestionAndGetNextQuestionFromQuestion(model);
  return generateViewForSurveyQuestion(nextQuestion);
}

The overload of RedirectToAction() which you are invoking requires route parameters, which your SurveyQuestion object cannot properly represent.

answered Jul 27, 2015 at 23:39

Peter Gluck

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Comments

Raj Karri · Accepted Answer · 2015-07-27 23:58:38Z

0

I think you can use TempData as below.

public ActionResult submitSurveyQuestion(SurveyQuestion model) 
    {
        SurveyQuestion nextQuestion = new SurveyQuestion();
        nextQuestion = submitSurveyQuestionAndGetNextQuestionFromQuestion(model);
      TempData["question"] = nextQuestion;
        return RedirectToAction("generateViewForSurveyQuestion");
    }

public SurveyQuestion submitSurveyQuestionAndGetNextQuestionFromQuestion(SurveyQuestion currentQuestion)
    {
        SurveyQuestion surveyQuestion = new SurveyQuestion();
        surveyQuestion.Question = "question";
        //...etc, this just sets all the question properties
        return surveyQuestion;
    }
public ActionResult generateViewForSurveyQuestion()
    {
        // TempDate[question] available here......
    }

answered Jul 27, 2015 at 23:58

Raj Karri

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1 Comment

Peter Gluck Over a year ago

TempData[] could be used to persist the object across invocations, but it is not necessary for this use case.

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