Develop Reference

Exclude items in an array in unity 2021

I've begun working on an early alpha menu for my game and I've was wondering how to exclude items in an array, specifically in unity. I'm trying to make every item except the currently used one. I don't know how I should go about it, if anyone could help, that would be amazing.
here's my current code:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[System.Serializable]
public class CS
{
public List<GameObject> CanvasButtons;
}
public class CanvasSwitcher : MonoBehaviour
{
public List<CS> Screen = new List<CS>();
static int switcher;
public static void ScreenSwitchPlus()
{
switcher += 1;
}
public static void ScreenSwitchMinus()
{
switcher -= 1;
}
public void Update()
{
foreach(GameObject l in Screen[switcher].CanvasButtons)
{
l.SetActive(true);
}
}
}

It would be wiser to use for loop instead of foreach loop here:
public void Update()
{
int ignore = 2;
for(int i = 0; i < Screen[switcher].CanvasButtons.Count; i++)
{
if(i != ignore)
Screen[switcher].CanvasButtons[i].SetActive(true);
else
Screen[switcher].CanvasButtons[i].SetActive(false);
}
}
It could be even shorter without if (admit less readable):
public void Update()
{
int ignore = 2;
for(int i = 0; i < Screen[switcher].CanvasButtons.Count; i++)
{
Screen[switcher].CanvasButtons[i].SetActive(i != ignore);
}
}
... and even shorter with taking CanvasButtons out of loop:
public void Update()
{
int ignore = 2;
var collection = Screen[switcher].CanvasButtons;
for(int i = 0; i < collection.Count; i++)
{
collection[i].SetActive(i != ignore);
}
}

I got it! I was a bit null-brained for a while there, I messed up a few values in the second for statement, but I got it. I'll post the code here. I keep forgetting little things in the math. Like I always say, I don't solve problems, I make them.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[System.Serializable]
public class CS
{
public List<GameObject> CanvasButtons;
}
public class CanvasSwitcher : MonoBehaviour
{
public List<CS> Screen = new List<CS>();
static int switcher;
public static void ScreenSwitchPlus()
{
switcher += 1;
}
public static void ScreenSwitchMinus()
{
switcher -= 1;
}
public void FixedUpdate()
{
List<CS> csco = Screen;
for(int i1 = 0; i1 < csco.Count;)
{
List<GameObject> collection = csco[i1].CanvasButtons;
for (int i = 0; i < collection.Count; i++)
{
collection[i].SetActive(i1 == switcher);
switch(i == collection.Count - 1)
{
case true:
i1++;
break;
}
}
}
}
}

I think you are making things too complicated.
It could simply be
public void Update()
{
for(var i = 0; i < Screen.Count; i++)
{
foreach(var button in Screen[i].CanvasButtons)
{
button.SetActive(i == switcher);
}
}
}
Two more points though.
First I would make sure that switcher is actually a valid value. You either want to clamp the value to stay within the index range like
public static void ScreenSwitchPlus()
{
switcher = Mathf.Clamp(switcher + 1, 0, Screen.Count);
}
public static void ScreenSwitchMinus()
{
switcher = Mathf.Clamp(switcher - 1, 0, Screen.Count);
}
or you could implement wrap around at the ends according to your needs like
public static void ScreenSwitchPlus()
{
switcher = (switcher + 1) % Screen.Count;
}
public static void ScreenSwitchMinus()
{
switcher -= 1;
if(switcher < 0) switcher = Screen.Count - 1;
}
and then finally as mentioned I wouldn't do this poll fetching the value in Update every frame at all but rather event driven.
If you really need to (I would claim it is just lazyness ;) ) have that value and methods static you could attach to an event like
private static event Action<int> OnSwitcherChanged;
public static void ScreenSwitchPlus()
{
switcher = (switcher + 1) % Screen.Count;
OnSwitcherChanged?.Invoke(switcher);
}
public static void ScreenSwitchMinus()
{
switcher -= 1;
if(switcher < 0) switcher = Screen.Count - 1;
OnSwitcherChanged?.Invoke(switcher);
}
and then listen to that event like
private void OnEnable()
{
OnSwitcherChanged += HandleSwitchChanged;
}
private void OnDisable()
{
OnSwitcherChanged -= HandleSwitchChanged;
}
private void HandleSwitchChanged(int newIndex)
{
for(var i = 0; i < Screen.Count; i++)
{
foreach(var button in Screen[i].CanvasButtons)
{
button.SetActive(i == switcher);
}
}
}

Try this
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[System.Serializable]
public class CS {
public List<GameObject> CanvasButtons;
}
public class CanvasSwitcher : MonoBehaviour {
public List<CS> Screen = new List<CS>();
private static bool m_changed = false;
private static int m_lastSwitcher = 0;
private static int m_switcher = 0;
static int switcher {
get {
return m_switcher;
}
set {
if ( switcher != value ) {
m_lastSwitcher = m_switcher;
m_changed = true;
m_switcher = value;
}
}
}
public static void ScreenSwitchPlus() {
switcher += 1;
}
public static void ScreenSwitchMinus() {
switcher -= 1;
}
private void Update() {
if ( m_changed ) {
UpdateCS();
m_changed = false;
}
}
void UpdateCS() {
if ( m_lastSwitcher < Screen.Count ) {
var canvasBtns = Screen[ m_lastSwitcher ].CanvasButtons;
for ( int i = 0; i < canvasBtns.Count; i++ ) {
canvasBtns[ i ].SetActive( false );
}
}
if ( switcher < Screen.Count ) {
var canvasBtns = Screen[ switcher ].CanvasButtons;
for ( int i = 0; i < canvasBtns.Count; i++ ) {
canvasBtns[ i ].SetActive( true );
}
}
}
}

Having problem with the Dictionary in unity

I am currently programming a game in which an infinite procedural city is generated. so far everything works but because it leads to laggs if there are too many objects in the scene I wanted to make a script in which objects only appear near the player. I watched this video for help:https://www.youtube.com/watch?v=xlSkYjiE-Ck. When I tried to link this to my script (GenerateBuilding script) this error came:ArgumentException:
An item with the same key has already been added. Key: (0.0, 1.0)
System.Collections.Generic.Dictionary...
I need help to make the script work in which the houses are generated as well as the planes do, they should only be showed when the player is nearby
---Relevant Lines---
(Endless City)
calling updateChunk function in update()(updateChunk/building function is in GenerateBuilding script)
public void UpdateBuildings()
{
for (int i = 0; i < buildingObjects.Count; i++)
{
buildingObjects[i].SetVisible(false);
}
buildingObjects.Clear();
}
adding to dictionary line 68-80(UpdateVisibleChunks function)
if (building.cityChunkDictionary.ContainsKey(viewedChunkCoord))
{
building.cityChunkDictionary[viewedChunkCoord].UpdateCityChunk(viewerPosition, viewedChunkCoord, chunkSize, maxViewDst);
if (building.cityChunkDictionary[viewedChunkCoord].IsVisible())
{
building.buildingObjects.Add(building.cityChunkDictionary[viewedChunkCoord]);
}
}
else
{
building.AddTest(viewedChunkCoord, chunkSize);
}
EndlessCity, CityChunk class
CityChunk function, sending position to GenerateBuilding script to instantiate buildings in right position.
building.requestBuildingSquad(positionV3);
GenerateBuilding relevant lines
builderH function, instantiates the buildings
public float builderH(GameObject[] obj, float Height, Vector3 position)
{
Transform objTrans = obj[Random.Range(0, obj.Length)].transform;
//Instantiate house Object
GameObject objekt = Instantiate(objTrans.gameObject, position + new Vector3(xOfsset * spaceBetween, Height, zOfsset * spaceBetween), transform.rotation);
float height = Test.transform.localScale.y;
objectsss.Add(objekt);
return height;
}
AddTest function, adds instantiates objects from builderH to a dictionary
public void AddTest(Vector2 viewedChunkCoord, float chunkSize)
{
for (int i = 0; i < objectsss.Count; i++)
{
cityChunkDictionary.Add(viewedChunkCoord, new Testing(objectsss[i]));
}
}
Testing class, testing function, adds objects to class
public Testing(GameObject obj)
{
MeshObject = obj;
}
that should be all relevant lines
full scripts(really similar)
EndlessCity Script(this scripts generates the planes and gives position for GenerateBuilding script)
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System;
public class EndlessCity : MonoBehaviour
{
public const float maxViewDst = 10;
public Transform viewer;
private GenerateBuilding building;
public static Vector2 viewerPosition;
int chunkSize;
int chunksVisibleInViewDst;
Dictionary<Vector2, CityChunk> terrainChunkDictionary = new Dictionary<Vector2, CityChunk>();
List<CityChunk> terrainChunksVisibleLastUpdate = new List<CityChunk>();
void Start()
{
chunkSize = 8 - 1;
chunksVisibleInViewDst = Mathf.RoundToInt(maxViewDst / chunkSize);
}
void Update()
{
viewerPosition = new Vector2(viewer.position.x, viewer.position.z);
UpdateVisibleChunks();
}
void UpdateVisibleChunks()
{
building = FindObjectOfType<GenerateBuilding>();
building.UpdateBuildings();
for (int i = 0; i < terrainChunksVisibleLastUpdate.Count; i++)
{
terrainChunksVisibleLastUpdate[i].SetVisible(false);
}
terrainChunksVisibleLastUpdate.Clear();
int currentChunkCoordX = Mathf.RoundToInt(viewerPosition.x / chunkSize);
int currentChunkCoordY = Mathf.RoundToInt(viewerPosition.y / chunkSize);
for (int yOffset = -chunksVisibleInViewDst; yOffset <= chunksVisibleInViewDst; yOffset++)
{
for (int xOffset = -chunksVisibleInViewDst; xOffset <= chunksVisibleInViewDst; xOffset++)
{
Vector2 viewedChunkCoord = new Vector2(currentChunkCoordX + xOffset, currentChunkCoordY + yOffset);
if (terrainChunkDictionary.ContainsKey(viewedChunkCoord))
{
terrainChunkDictionary[viewedChunkCoord].UpdateTerrainChunk();
if (terrainChunkDictionary[viewedChunkCoord].IsVisible())
{
terrainChunksVisibleLastUpdate.Add(terrainChunkDictionary[viewedChunkCoord]);
}
}
else
{
terrainChunkDictionary.Add(viewedChunkCoord, new CityChunk(viewedChunkCoord, chunkSize, transform));
}
if (building.cityChunkDictionary.ContainsKey(viewedChunkCoord))
{
building.cityChunkDictionary[viewedChunkCoord].UpdateCityChunk(viewerPosition, viewedChunkCoord, chunkSize, maxViewDst);
if (building.cityChunkDictionary[viewedChunkCoord].IsVisible())
{
building.buildingObjects.Add(building.cityChunkDictionary[viewedChunkCoord]);
}
}
else
{
building.AddTest(viewedChunkCoord, chunkSize);
}
}
}
}
public class CityChunk
{
private GenerateBuilding building;
public GameObject meshObject;
public Vector3 positionV3;
Vector2 position;
Bounds bounds;
public CityChunk(Vector2 coord, int size, Transform parent)
{
building = FindObjectOfType<GenerateBuilding>();
position = coord * size;
bounds = new Bounds(position, Vector2.one * size);
positionV3 = new Vector3(position.x, 0, position.y);
int xPosition = building.xLength / 2;
int zPosition = building.zLength / 2;
float xOfsset = building.xOfsset;
float zOfsset = building.zOfsset;
float spaceBetween = building.spaceBetween;
//Instantiate plane
meshObject = Instantiate(building.groundObject, positionV3 + new Vector3((xPosition + xOfsset) * spaceBetween, -.5f, (xPosition + 1 + zOfsset) * spaceBetween), Quaternion.identity);
SetVisible(false);
building.requestBuildingSquad(positionV3);
}
public void UpdateTerrainChunk()
{
float viewerDstFromNearestEdge = Mathf.Sqrt(bounds.SqrDistance(viewerPosition));
bool visible = viewerDstFromNearestEdge <= maxViewDst;
SetVisible(visible);
}
public void SetVisible(bool visible)
{
meshObject.SetActive(visible);
}
public bool IsVisible()
{
return meshObject.activeSelf;
}
}
}
GenerateBuilding(this script generates Buildings on the planes)
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class GenerateBuilding : MonoBehaviour
{
public int minHeight = 2;
public int maxHeight = 8;
public int cubeTileX;
public int cubeTileZ;
public int xLength;
public int zLength;
public float spaceBetween;
public float xOfsset;
public float zOfsset;
public GameObject TesObject;
public GameObject[] Base;
public GameObject[] secondB;
public GameObject[] roof;
public GameObject groundObject;
public List<GameObject> objectsss;
public Dictionary<Vector2, Testing> cityChunkDictionary = new Dictionary<Vector2, Testing>();
public List<Testing> buildingObjects = new List<Testing>();
public GameObject Test;
void Start()
{
//requestBuildingSquad(this.transform.position);
}
void Update()
{
if (Input.GetKeyDown(KeyCode.I))
{
//
}
}
public void requestBuildingSquad(Vector3 position)
{
//*getting the middle of the city squad
int xPosition = xLength / 2;
int zPosition = zLength / 2;
//*
for (int z = 0; z < zLength; z++)
{
zOfsset++;
for (int x = 0; x < xLength; x++)
{
GenerateBuildings(position);
}
xOfsset = 0;
}
zOfsset = 0;
}
public void GenerateBuildings(Vector3 position)
{
int bHeight = Random.Range(minHeight, maxHeight);
float bOfsset = 0;
bOfsset += builderH(Base, bOfsset, position);
for (int i = 0; i < bHeight; i++)
{
bOfsset += builderH(secondB, bOfsset, position);
}
bOfsset += builderH(roof, bOfsset, position);
xOfsset++;
}
public float builderH(GameObject[] obj, float Height, Vector3 position)
{
Transform objTrans = obj[Random.Range(0, obj.Length)].transform;
//Instantiate house Object
GameObject objekt = Instantiate(objTrans.gameObject, position + new Vector3(xOfsset * spaceBetween, Height, zOfsset * spaceBetween), transform.rotation);
float height = Test.transform.localScale.y;
objectsss.Add(objekt);
return height;
}
public void AddTest(Vector2 viewedChunkCoord, float chunkSize)
{
for (int i = 0; i < objectsss.Count; i++)
{
cityChunkDictionary.Add(viewedChunkCoord, new Testing(objectsss[i]));
}
}
public void UpdateBuildings()
{
for (int i = 0; i < buildingObjects.Count; i++)
{
buildingObjects[i].SetVisible(false);
}
buildingObjects.Clear();
}
public class Testing
{
public GameObject MeshObject;
Vector2 position;
Bounds bounds;
public Testing(GameObject obj)
{
MeshObject = obj;
}
public void SetVisible(bool visiblee)
{
MeshObject.SetActive(visiblee);
}
public bool IsVisible()
{
return MeshObject.activeSelf;
}
public void UpdateCityChunk(Vector3 viewerPosition, Vector2 coord, int size, float maxViewDst)
{
position = coord * size;
bounds = new Bounds(position, Vector2.one * size);
float viewerDstFromNearestEdge = Mathf.Sqrt(bounds.SqrDistance(viewerPosition));
bool visible = viewerDstFromNearestEdge <= maxViewDst;
SetVisible(visible);
}
}
}

The problem is that you are trying to add twice elements with the same key.
here is the documentation of the Add method for dictionaries, and as it states, trying to add an existing key throws an error.
You can either use the TryAdd method, which adds an item only if the key doesn't exist already in the dictionary, or update the value with the existing key as you can see here.

Issue in Unity, NullReferenceException: Object reference not set to an instance of an object [duplicate]

This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 5 years ago.
thanks for reading, I am working on a small memory card game in C# using Unity. When I run a certain scene I am receiving constant errors.
The errors are as follows:
"NullReferenceException: Object reference not set to an instance of an object
Card.SetUpArt () (at Assets/Scripts/Card.cs:31)
Pairs.SetUpDeck () (at Assets/Scripts/Pairs.cs:62)
Pairs.Update () (at Assets/Scripts/Pairs.cs:23)"
My code is:
using System.Collections;
using System.Collections.Generic;
using UnityEngine.UI;
using UnityEngine;
public class Card : MonoBehaviour {
public static bool NO_TURN = false;
[SerializeField]
private int cardState; //state of card
[SerializeField]
private int cardNumber; //Card value (1-13)
[SerializeField]
private bool _setUp = false;
private Sprite cBack; //card back (Green square)
private Sprite cFace; //card face (1-10 JQKA)
private GameObject pairsManager;
void Begin()
{
cardState = 1; //cards face down
pairsManager = GameObject.FindGameObjectWithTag("PairsManager");
}
public void SetUpArt()
{
cBack = pairsManager.GetComponent<Pairs>().GetBack(); //<--error
cFace = pairsManager.GetComponent<Pairs>().GetFace(cardNumber);
turnCard();//turns the card
}
public void turnCard() //handles turning of card
{
if (cardState == 0)
{
cardState = 1;
}
else if(cardState == 1)
{
cardState = 0;
}
if (cardState == 0 && !NO_TURN)
{
GetComponent<Image>().sprite = cBack; // shows card back
}
else if (cardState == 1 && !NO_TURN)
{
GetComponent<Image>().sprite = cFace; // shows card front
}
}
//setters and getters
public int Number
{
get {return cardNumber;}
set { cardNumber = value;}
}
public int State
{
get { return cardState; }
set { cardState = value; }
}
public bool SetUp
{
get { return _setUp; }
set { _setUp = value; }
}
public void PairCheck()
{
StartCoroutine(pause ());
}
IEnumerator pause()
{
yield return new WaitForSeconds(1);
if (cardState == 0)
{
GetComponent<Image>().sprite = cBack;
}
else if (cardState == 1)
{
GetComponent<Image>().sprite = cFace;
}
}
}
And:
using System.Collections;
using System.Collections.Generic;
using UnityEngine.UI;
using UnityEngine.SceneManagement;
using UnityEngine;
public class Pairs : MonoBehaviour {
public Sprite[] cardFace; //array of card faces
public Sprite cardBack;
public GameObject[] deck; //array of deck
public Text pairsCount;
private bool deckSetUp = false;
private int pairsLeft = 13;
// Update is called once per frame
void Update () {
if (!deckSetUp)
{
SetUpDeck();
}
if (Input.GetMouseButtonUp(0)) //detects left click
{
CheckDeck();
}
}//Update
void SetUpDeck()
{
for(int i = 0; i <deck.Length; i++)//resets cards
{
deck[i].GetComponent<Card>().SetUp = false;
}
for (int ix = 0; ix < 2; ix++) //sets up cards twice,
{
for(int i = 1; i < 14; i++)//sets up card value (2-10 JQKA)
{
bool test = false;
int val = 0;
while (!test)
{
val = Random.Range(0, deck.Length);
test = !(deck[val].GetComponent<Card>().SetUp);
}//while
//sets up cards
deck[val].GetComponent<Card>().Number = i;
deck[val].GetComponent<Card>().SetUp = true;
}//nested for
}//for
foreach (GameObject crd in deck)
{
crd.GetComponent<Card>().SetUpArt();
}
if (!deckSetUp)
{
deckSetUp = true;
}
}//SetUpDeck
public Sprite GetBack()
{
return cardBack;
}//getBack
public Sprite GetFace(int i)
{
return cardFace[i - 1];
}//getFace
void CheckDeck()
{
List < int > crd = new List<int>();
for(int i = 0; i < deck.Length; i++)
{
if(deck[i].GetComponent<Card>().State == 1)
{
crd.Add(i);
}
}
if(crd.Count == 2)
{
CompareCards(crd);
}
}//CheckDeck
void CompareCards(List<int> crd)
{
Card.NO_TURN = true; //stops cards turning
int x = 0;
if(deck[crd[0]].GetComponent<Card>().Number ==
deck[crd[1]].GetComponent<Card>().Number)
{
x = 2;
pairsLeft--;
pairsCount.text = "PAIRS REMAINING: " + pairsLeft;
if(pairsLeft == 0) // goes to home screen when game has been won
{
SceneManager.LoadScene("Home");
}
}
for(int j = 0; j < crd.Count; j++)
{
deck[crd[j]].GetComponent<Card>().State = x;
deck[crd[j]].GetComponent<Card>().PairCheck();
}
}//CompareCards
}
Any help anyone can offer would be greatly appreciated. Thank you in advance.
Link to GitHub Repository

I don't have knowledge about C#, as I'm working with java. You should initialize your variables. For more information I found this link What is a NullReferenceException, and how do I fix it?

How to display health using GUIText?

I want to display my health as the GUIText and decreasing when the player hits. How to code based on my health script?
Here is my healthscript
using UnityEngine;
using System.Collections;
public class HealthScript : MonoBehaviour {
public static HealthScript instance;
public int hp = 1;
private GUIText scoreReference;
private GUIText highscoreReference;
private static int _highscore = -1;
public int highscore {
get { if (_highscore == -1)
_highscore = PlayerPrefs.GetInt("Highscore", 0);
return _highscore;
}
set {
if (value > _highscore) {
_highscore = value;
highscoreReference.text = _highscore.ToString();
PlayerPrefs.SetInt("Highscore", _highscore);
}
}
}
public bool isEnemy = true;
private static int points;
public void Damage(int damageCount) {
hp -= damageCount;
if (hp <= 0)
{
// Dead!
Destroy(gameObject);
points++;
scoreReference.text = points.ToString();
}
}
public void gameEnd() {
highscore = points;
points = 0;
}
void Start()
{
scoreReference = GameObject.Find("Score").guiText;
highscoreReference = GameObject.Find("HighScore").guiText;
scoreReference.text = points.ToString();
highscoreReference.text = highscore.ToString ();
instance = this;
}
UPDATE: I DON'T WANT TO DISPLAY ENEMY HEALTH, THIS SCRIPT WAS ATTACHED TO EVERY ENEMY

I recommend you to use OnGui method always to show the interface of the game
void OnGUI(){
GUI.color = Color.red;
GUI.Label(new Rect (20,20,200,20), "Health = " + hp);
}
All the documentation you need to understand this code is here:
GUI.Label http://docs.unity3d.com/ScriptReference/GUI.Label.html
OnGui method: http://docs.unity3d.com/ScriptReference/MonoBehaviour.OnGUI.html
Hope this help you, ask if you have any troubles with this code!

You can use a variable to show on the GUI with C# easily by doing:
var myNiceVariable = "Showing the health values!";
var guiText = GameObject.Find("GUI Text").GetComponent(GUIText);
guiText.text = myNiceVariable;
Or you can use the OnGui method, you can add to your script:
void OnGui(){
GUI.Label(new Rect (5,5,10,100), "Health: " + hp);
}
Code taken from here and here.

Unity C# Object reference not set to an instance of an object

I keep getting the error Object reference not set to an instance of an object on line 64 and I can't figure out what I need to do
Everything is working like the lives are showing up and the timer and the score is but the score isn't increasing if you can tell me what is wrong I would be so thankful
Here's my code:
using UnityEngine;
using System.Collections;
public class Player : MonoBehaviour {
private CountdownTimer myTimer;
private int score = 0;
private int lives = 3;
private int DEATH_Y = -10;
public Texture2D LivesLeft1;
public Texture2D LivesLeft2;
public Texture2D LivesLeft3;
public int GetScore(){
return score;
}
public int GetLives()
{
return lives;
}
private void Start()
{
myTimer = GetComponent<CountdownTimer>();
}
private void Update()
{
float y = transform.position.y;
if (y < DEATH_Y) {
MoveToStartPosition();
lives--;
}
if (score == 10)
{
Application.LoadLevel("Level2");
}
if (lives == 0)
{
Application.LoadLevel("GameOver");
}
}
private void OnGUI()
{
GUILayout.BeginHorizontal ();
DisplayLives();
int secondsLeft = myTimer.GetSecondsRemaining();//this is line 64
string timeMessage = "Seconds left = " + secondsLeft;
GUILayout.Label(timeMessage);
string scoreMessage = "Score = " + score;
GUILayout.Label (scoreMessage);
}
private void DisplayLives()
{
int playerLives = GetLives();
if (1 == playerLives) {
GUILayout.Label(LivesLeft1);
}
if (2 == playerLives)
{
GUILayout.Label(LivesLeft2);
}
if(3 == playerLives){
GUILayout.Label(LivesLeft3);
}
}
private void MoveToStartPosition()
{
Vector3 startPosition = new Vector3(0,5,0);
transform.position = startPosition;
}
/**
* what increases the score
* anything with the tag Hidden
*/
private void OnTriggerEnter(Collider c)
{
string tag = c.tag;
if("Hidden" == tag)
{
score++;
}
}
}

Are you sure that your GameObject have the Component called CountdownTimer?
Also, change the Start function to Awake, because that line is not depending on anything else.