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Question null reference exception

Discussion in 'Scripting' started by jojo57957, Mar 27, 2023.

  1. jojo57957


    Mar 22, 2023
    I keep getting a null reference exception when I try to reference my character manger script in my testing script

    Character manger:
    Code (CSharp):
    1. using System.Collections;
    2. using System.Collections.Generic;
    3. using UnityEngine;
    4. using UnityEngine.UI;
    6. /// <summary>
    7. /// Responsibvle for adding and manging chacters in a scene
    8. /// </summary>
    9. public class CharcterManger : MonoBehaviour
    10. {
    11.     public static CharcterManger instance;
    13.     /// <summary>
    14.     /// All chacters must be attached to the charcter pannel
    15.     /// </summary>
    16.     public RectTransform CharactersPannel;
    18.     /// <summary>
    19.     /// a list of every chacter in the scene
    20.     /// </summary>
    21.     public List<Character> characters = new List<Character>();
    23.     /// <summary>
    24.     /// easy look up for our chacters
    25.     /// </summary>
    26.     public Dictionary<string, int> characterDictionary = new Dictionary<string, int>();
    28.     void awake ()
    29.     {
    30.         instance = this;
    31.     }
    34.     /// <summary>
    35.     /// try to get charcter from the list
    36.     /// </summary>
    37.     /// <param name="charactersName"></param>
    39.     public Character getCharacter(string charactersName, bool createCharacterIfDoesNotExist = true)
    40.     {
    41.         //search our libary to see if a chacter is alredy in the scene
    42.         int index = -1;
    43.         if (characterDictionary.TryGetValue(charactersName, out index))
    44.         {
    45.             return characters[index];
    46.         }
    47.         else if(createCharacterIfDoesNotExist)
    48.         {
    49.             return createCharacter(charactersName);
    50.         }
    52.         return null;
    54.     }
    56.     /// <summary>
    57.     /// create the chacter
    58.     /// </summary>
    59.     /// <param name="characterName"></param>
    60.     /// <returns></returns>
    61.     public Character createCharacter(string characterName)
    62.     {
    63.         Character newCharacter = new Character(characterName);
    65.         characterDictionary.Add (characterName, characters.Count);
    66.         characters.Add(newCharacter);
    68.             return newCharacter;
    69.     }
    70. }

    Code (CSharp):
    1. using System.Collections;
    2. using System.Collections.Generic;
    3. using UnityEngine;
    5. public class ChacterTesting : MonoBehaviour
    6. {
    7.     public Character Reinart;
    8.     public Character Lynex;
    10.     // Start is called before the first frame update
    11.     void Start()
    12.     {
    13.         Reinart = CharcterManger.instance.getCharacter("Reinart");
    14.         Lynex = CharcterManger.instance.getCharacter("Lynex");
    15.     }
    16. }
  2. FrankvHoof


    Nov 3, 2014
    void awake ()

    This will not run. Unity's built-in method is called Awake, not awake.
    MelvMay likes this.
  3. MelvMay


    Unity Technologies

    May 24, 2013
    Also note, you've named some of your stuff "Charcter" and some "character". That might catch you out at some point.
  4. Kurt-Dekker


    Mar 16, 2013
    How to fix a NullReferenceException error

    Three steps to success:
    - Identify what is null <-- any other action taken before this step is WASTED TIME
    - Identify why it is null
    - Fix that

    As others note above, you must eliminate 100% of your typing mistakes.

    Tutorials and example code are great, but keep this in mind to maximize your success and minimize your frustration:

    How to do tutorials properly, two (2) simple steps to success:

    Step 1. Follow the tutorial and do every single step of the tutorial 100% precisely the way it is shown. Even the slightest deviation (even a single character!) generally ends in disaster. That's how software engineering works. Every step must be taken, every single letter must be spelled, capitalized, punctuated and spaced (or not spaced) properly, literally NOTHING can be omitted or skipped.

    Fortunately this is the easiest part to get right: Be a robot. Don't make any mistakes.

    If you get any errors, learn how to read the error code and fix your error. Google is your friend here. Do NOT continue until you fix your error. Your error will probably be somewhere near the parenthesis numbers (line and character position) in the file. It is almost CERTAINLY your typo causing the error, so look again and fix it.

    Step 2. Go back and work through every part of the tutorial again, and this time explain it to your doggie. See how I am doing that in my avatar picture? If you have no dog, explain it to your house plant. If you are unable to explain any part of it, STOP. DO NOT PROCEED. Now go learn how that part works. Read the documentation on the functions involved. Go back to the tutorial and try to figure out WHY they did that. This is the part that takes a LOT of time when you are new. It might take days or weeks to work through a single 5-minute tutorial. Stick with it. You will learn.

    Step 2 is the part everybody seems to miss. Without Step 2 you are simply a code-typing monkey and outside of the specific tutorial you did, you will be completely lost. If you want to learn, you MUST do Step 2.

    Of course, all this presupposes no errors in the tutorial. For certain tutorial makers (like Unity, Brackeys, Imphenzia, Sebastian Lague) this is usually the case. For some other less-well-known content creators, this is less true. Read the comments on the video: did anyone have issues like you did? If there's an error, you will NEVER be the first guy to find it.

    Beyond that, Step 3, 4, 5 and 6 become easy because you already understand!

    Finally, when you have errors, don't post here... just go fix your errors! Here's how:

    Remember: NOBODY here memorizes error codes. That's not a thing. The error code is absolutely the least useful part of the error. It serves no purpose at all. Forget the error code. Put it out of your mind.

    The complete error message contains everything you need to know to fix the error yourself.

    The important parts of the error message are:

    - the description of the error itself (google this; you are NEVER the first one!)
    - the file it occurred in (critical!)
    - the line number and character position (the two numbers in parentheses)
    - also possibly useful is the stack trace (all the lines of text in the lower console window)

    Always start with the FIRST error in the console window, as sometimes that error causes or compounds some or all of the subsequent errors. Often the error will be immediately prior to the indicated line, so make sure to check there as well.

    Look in the documentation. Every API you attempt to use is probably documented somewhere. Are you using it correctly? Are you spelling it correctly?

    All of that information is in the actual error message and you must pay attention to it. Learn how to identify it instantly so you don't have to stop your progress and fiddle around with the forum.
  5. Homicide


    Oct 11, 2012
    Man, the people make this real easy on you dont they. @Kurt-Dekker
    Ryiah likes this.