Error: An object reference is required for the non-static field, what does it mean?

Questions & Answers
1

What is wrong ?
Error said
Assets\Gamemanager.cs(18,22): error CS0120: An object reference is required for the non-static field, method, or property ‘SceneManager.GetActiveScene()’

What do it means???

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

public class Gamemanager : MonoBehaviour
{

public static LevelControl instance = null;
public GameObject completeLevelUI;

int sceneIndex, levelPassed;

void Start (){
	//get the level index first.
    sceneIndex = SceneManager.GetActiveScene ().buildIndex;

	levelPassed = PlayerPrefs.GetInt ("LevelPassed");

}

public void CompleteLevel()
{
	completeLevelUI.SetActive (true);

	if (sceneIndex == 6)
		Invoke ("loadMainMenu", 1f);
	else {
		if (levelPassed < sceneIndex)
			PlayerPrefs.SetInt ("LevelPassed", sceneIndex);
		
	}
}

}

2

Do you have a custom class called SceneManager in your project?

If so, it conflicts with the Unity’s SceneManager.

To fix:

void Start (){
     //get the level index first.
     sceneIndex = UnityEngine.SceneManagement.SceneManager.GetActiveScene ().buildIndex;
     levelPassed = PlayerPrefs.GetInt ("LevelPassed");
 }