错误帮助-UnityException：声明变量时不允许调用此函数

Question

I'm getting the following runtime error...

"UnityException: You are not allowed to call this function when declaring a variable. Move it to the line after without a variable declaration. If you are using C# don't use this function in the constructor or field initializers, Instead move initialization to the Awake or Start function."

The stack trace:

UnityEngine.GameObject..ctor () (at C:/buildslave/unity/build/artifacts/generated/common/runtime/UnityEngineGameObje‌​ctBindings.gen.cs:419)
BallManager..ctor ()
ArcadeBallManager..ctor ()
UnityEngine.GameObject:AddComponent()
BasicGame:Start() (at Assets/BasicGame.cs:106)

This seems to happen in a script where I use exampleObject.AddComponent<aType>() or exampleObject.GetComponent<aType>() .

I have tried many ways of resolving this, starting with moving the lines of code to Awake() and Start Functions() (as suggested in the error log).

I have tried declaring the variable locally, globally, with different access modifiers and in addition I have played around with immediate vs delayed assignment after declaration.

I have also tried a variety of other "fixes" found on other posts ranging from restarting Unity to recreating the script etc.

I'm at the point where I'm wondering if I'm suffering from some kind of fundamental knowledge gap relating to this.

I'm not looking for a code fix here, I'm looking to understand what is going on so if anyone understands this error, can they shed some light on it please.

Additional details that could be important... I'm trying to choose a management system dynamically based on game type eg classicManager, specialManager, baseManager. The management classes share a base class. I'm going for polymorphism to address the base class... See below for pseudo example

if(gameType == specialManager)
{
   manager = exampleObj.AddComponent<ClassicManager>() as baseManager;
} 

Any help would be greatly appreciated.

New Code For Arx Added.

using UnityEngine;
using System.Collections;
using System;

public class BasicGame : MonoBehaviour {

    public GameObject ball_manager_obj;
    //public BallManager ball_manager_script;// = BallManager();
    // Can Be : "NumBallClasic"  or "NumballArcade" etc.

    //TEST...

    public ArcadeBallManager arcd;
    public ClassicNumBallManager clsc;


    //...TEST END

    public string game_type = "Arcade";

    public int seconds_left;
    public int minutes_left;

    public int game_length_mins = 2;

    public string game_time_string = "";

    public bool game_over = false;
    public bool game_paused = false;

    public int score = 0;

    public float ball_interval_min = 0.2f;
    public float ball_interval_max = 0.6f;
    public float ball_interval = 0.5f;

    public float ball_check_interval = 0.1f;


    public Camera the_cam;

    public GameObject wall_container;
    public WallScript wall_script;

    public GameObject end_zone_container;
    public EndZoneScript end_zone_script;

    public Color lerp_colour_a = Color.white;
    public Color lerp_colour_b = new Color(0.2f,0.6f,0.8f,1.0f);
    public Color intended_colour = Color.white;
    public Color prev_colour = Color.white;

    public bool is_set_up = false;
    // Use this for initialization
    void Start() 
    {

        the_cam = GameObject.Find ("Main Camera").GetComponent<Camera> ();
        the_cam.backgroundColor = intended_colour;
        //this.gameObject.transform.localScale = (new Vector3(the_cam.rect.width, the_cam.rect.height,0));

        ball_manager_obj = new GameObject ();
        ball_manager_obj.transform.SetParent (this.gameObject.transform);
        ball_manager_obj.name = "BallManagerObj";

        wall_container = new GameObject ();
        wall_container.name = "WallContainer";
        wall_container.transform.SetParent (this.gameObject.transform);
        wall_container.AddComponent<WallScript>();
        wall_script = wall_container.GetComponent<WallScript> ();
        wall_script.createWalls ();

        end_zone_container = new GameObject ();
        end_zone_container.name = "EndZoneContainer";
        end_zone_container.transform.SetParent (this.gameObject.transform);
        end_zone_container.AddComponent<EndZoneScript> ();
        end_zone_script = end_zone_container.GetComponent<EndZoneScript> ();
        end_zone_script.createEndZone ();

        setGameType (game_type); //<<<<--TO BE SET SET VIA USER Eventually

        //chooseBallManager(ball_manager_obj, ball_manager_script);

        if(game_type == "NumBallClasic")
        {

            seconds_left = 0;
            minutes_left = game_length_mins;
            game_time_string = ("" + game_length_mins + ":00");

            BallManager ball_manager_script =      ((BallManager)ball_manager_obj.AddComponent<ClassicNumBallManager>());
            //return b_man;

        }
        if(game_type == "Arcade")
        {

            seconds_left = 0;
            minutes_left = game_length_mins;
            game_time_string = ("" + game_length_mins + ":00");

            if(ball_manager_obj != null)
            {

                BallManager ball_manager_script = (BallManager)ball_manager_obj.gameObject.AddComponent<ArcadeBallManager>();
            }
            else
            {
                ball_manager_obj = new GameObject ();
                BallManager ball_manager_script = (BallManager)ball_manager_obj.gameObject.AddComponent<ArcadeBallManager>();
                //ball_manager_script =  ball_manager_obj.GetComponent<ArcadeBallManager>();
            }


            //ArcadeBallManager nu_b_man = new ArcadeBallManager();
            //BallManager b_man = nu_b_man as BallManager;

            //return b_man;

        }
        else
        {
            seconds_left = 0;
            minutes_left = game_length_mins;

            game_time_string = ("" + game_length_mins + ":00");

            BallManager ball_manager_script =  ((BallManager)ball_manager_obj.AddComponent<ArcadeBallManager>());

            //BallManager b_man = new ArcadeBallManager() as BallManager;
            //return b_man;

        }


    }

New Code Added For 31eee384: (Note, class hardly touched - get sprite simply returns a new sprite for testing purposes atm)

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class ArcadeBallManager : BallManager {


    // Use this for initialization
    void Start () 
    {


    }

    // Update is called once per frame
    void Update () 
    {


    }


    public override Sprite getActiveSprite (string b_type)
    {
        //SendActiveSprite
        Sprite spr = new Sprite();

        return spr;
    }
}

Answer 1

In Short...

CHECK, CHECK AND CHECK AGAIN!

If you haven't found the problem, repeat the above step.

The problem was as 31eee384 pointed out... Burried deep in my base class there was a line that read something like:

GameObject obj = new GameObject();

To fix this error was simply a matter of initialising the GameObject inside a function eg

GameObject obj;

...

public void aFunc()
{
    obj = new GameObject();
}

NOTE: The error reads "... Instead move initialization to the Awake or Start function." - this was NOT working IN THIS PARTICULAR CASE. continue reading to find out more.

Although the correct and basic answer is as above, I shall explain the circumstances that led me to this frustratingly simple error incase anyone else has made the same mistake...

Way earlier, I had run into a null reference error stemming from code similar to the above. I was originally initialising the GameObject in the Start() function and could not figure out why I was receiving the null reference exception. As a work around I initialised the GameObject just outside the function I was using it in as follows (and as mentioned at the top)...

GameObject obj = new GameObject();

This line became berried in my code and forgotten about, as the fix seemed to work until I ran into the "...You are not allowed to call this function when declaring a variable" error.

The simple null reference error & the problem with "... Instead move initialization to the Awake or Start function." ...

The Start() function was not firing in the base class because the class extending it was also using the Start() function. HEAD SLAP MOMENT

The complete fix:

1) Make sure you ONLY initialise Objects INSIDE a function.

2) Ensure the function you initialise with actually runs in the base class.

In my case I changed the name of the Start() function in the base class to InitBase(). I then called this from the extended class.

Hope this helps :)