hi everyone, im a newbie in coding as of now, and i cant find what’s wrong with my coding.
im using this coding for my project for end year study.
public class QuestionSetup : MonoBehaviour
{
public List<QuestionData> questions;
private QuestionData currentQuestion;
private TextMeshProUGUI questionText;
private TextMeshProUGUI categoryText;
private AnswerButton[] answerButtons;
private int correctAnswerChoice;
private void Awake()
{
// Get all the questions ready
GetQuestionAssets();
}
// Start is called before the first frame update
public void Start()
{
//Get a new question
SelectNewQuestion();
// Set all text and values on screen
SetQuestionValues();
// Set all of the answer buttons text and correct answer values
SetAnswerValues();
}
// Update is called once per frame
void Update()
{
}
public void GetQuestionAssets()
{
// Get all of the questions from the questions folder
//questions = new List<QuestionData>(Resources.LoadAll<QuestionData>("Pertanyaan"));
}
private void SelectNewQuestion()
{
// Get a random value for which question to choose
int randomQuestionIndex = Random.Range(0, questions.Count);
//Set the question to the randon index
currentQuestion = questions[randomQuestionIndex];
// Remove this question from the list so it will not be repeared (until the game is restarted)
questions.RemoveAt(randomQuestionIndex);
}
private void SetQuestionValues()
{
// Set the question text
questionText.text = currentQuestion.question;
// Set the category text
categoryText.text = currentQuestion.category;
}
private void SetAnswerValues()
{
// Randomize the answer button order
List<string> answers = RandomizeAnswers(new List<string>(currentQuestion.answers));
// Set up the answer buttons
for (int i = 0; i < answerButtons.Length; i++)
{
// Create a temporary boolean to pass to the buttons
bool isCorrect = false;
// If it is the correct answer, set the bool to true
if (i == correctAnswerChoice)
{
isCorrect = true;
}
answerButtons[i].SetIsCorrect(isCorrect);
answerButtons[i].SetAnswerText(answers[i]);
}
}
private List<string> RandomizeAnswers(List<string> originalList)
{
bool correctAnswerChosen = false;
List<string> newList = new List<string>();
for (int i = 0; i < answerButtons.Length; i++)
{
// Get a random number of the remaining choices
int random = Random.Range(0, originalList.Count);
// If the random number is 0, this is the correct answer, MAKE SURE THIS IS ONLY USED ONCE
if (random == 0 && !correctAnswerChosen)
{
correctAnswerChoice = i;
correctAnswerChosen = true;
}
// Add this to the new list
newList.Add(originalList[random]);
//Remove this choice from the original list (it has been used)
originalList.RemoveAt(random);
}
return newList;
}
}
and the error was in between line 24 and 54. did anyone know whats wrong about this line?, also the error was
NullReferenceException: Object reference not set to an instance of an object
QuestionSetup.SetQuestionValues () (at Assets/QuestionSetup.cs:60)
QuestionSetup.Start () (at Assets/QuestionSetup.cs:30)
once again thank you for your time seeing this topic
I mean the error tells you exactly where it happened: Line 60 of the QuestionSetup component.
You’ve removed the imports from the code example you posted, so the line 60 that we can see doesn’t actually line up with anything, so it’s hard to give specific help here.
Nonetheless solving a null ref is always, always the same process:
1: Work out what is null ← the most important step
2: Work out WHY it’s null
3: Stop it being null
Identify what is null ← any other action taken before this step is WASTED TIME
Identify why it is null
Fix that.
Expect to see this error a LOT. It’s easily the most common thing to do when working. Learn how to fix it rapidly. It’s easy. See the above link for more tips.
You need to figure out HOW that variable is supposed to get its initial value. There are many ways in Unity. In order of likelihood, it might be ONE of the following:
drag it in using the inspector
code inside this script initializes it
some OTHER external code initializes it
? something else?
This is the kind of mindset and thinking process you need to bring to this problem:
At my dayjob i have used nullable reference types for a few years now (you need to explicit tell the compiler that null is accepted for a reference type variable).
It works very well and the code becomes much more stable and maintainable. Sadly it wouldnt play nice with unity since the constructor is required to set these fields.
But it would sure had been nice and the code base would benefit greatly from it.
Also now with the new required keyword you dont need to use the constructor but can use object initilizers.
@justfat_han The most disturbing is that lack of initialisation sometimes doesn’t trigger an error message. You’re lucky it did here.
So, before anything else always make sure your variables have been initialised either by code or in the Inspector if it’s a public or serialised private variable.
Obviously it only applies to reference types, NOT value types.
Second, you have to actually attempt to dereference (read, write or execute) the null value (obviously), and it must be null at the moment you attempt the dereference.
Unity, C# (and many other contexts) are rife with implicit initialization and part of using the context effectively is to undersatnd initialization.
In the case of Unity, here are SOME of the things might affect initialization:
Serialized / public fields in Unity are initialized as a cascade of possible values, each subsequent value (if present) overwriting the previous value:
what the class constructor makes (either default(T) or else field initializers, eg “what’s in your code”)
what may be saved with the prefab
what may be saved with the prefab override(s)/variant(s)
what may be saved in the scene and not applied to the prefab
what may be changed in the scene and not yet saved to disk
what may be changed in OnEnable(), Awake(), Start(), or even later
Make sure you only initialize things at ONE of the above levels, or if necessary, at levels that you specifically understand in your use case. Otherwise errors will seem very mysterious.
