Nullreferenceexception, Struct, Array, List

I found the following script on the forums and it works well until targets are destroyed, then throws the aforementioned exception. The error occurs around line 53. I’ve tried adding “if (target != null)” to the script and get the following error:

Assets/_Scripts/TargetingHUD.cs(53,29): error CS0019: Operator !=' cannot be applied to operands of type TargetingHUD.TargetStruct’ and `null’

Been looking for a way around this for a few hours now without much luck. Any help would be appreciated.

using UnityEngine;
using System.Collections;
using System.Collections.Generic;               //Use this so you can manipulate Lists

public class TargetingHUD : MonoBehaviour
{
	public Texture2D targetIcon;                //The target icon that will be placed in front of targets
	public float maxTargetIconSize = 300f;      //The maximum size of icons when close to the target
	public float minTargetIconSize = 20f;        //The minimum size of icons when they appear (far from the target)
	public float maxDistanceDisplay = 10f;      //The maximum distance from where you can see the icons appearing
	public float minDistanceDisplay = 2f;       //The minimum distance from where you see the icons disappearing when too close
	public float smoothGrowingParameter = 25f;  //The speed of the growing effect on icons
	public float smoothMovingParameter = 25f;   //The moving speed of items : high values means the icon is "attached" to the item
	public bool directViewEnabled = true;       //If you want to allow icon display even if targets aren't in direct view for the player

	public struct TargetStruct                  //Structure that contain every icon informations
	{
		public GameObject item;                 //-the item the icon is linked to
		public Vector3 screenPos;               //-the screen position of the icon (!= world position)
		public float xSize, ySize;              //-the current size of the icon on the screen
		public float xPos, yPos;                //-the current coordinates of the screen position
		public float xTargetSize, yTargetSize;  //-the coordinates you want the icon to reach
		public float xTargetPos, yTargetPos;    //-the size you want the icon to reach on the screen
		public float distance;                  //-the distance between player and the item linked to the icon
		public bool directView;                 //-tells you if the item is in direct view or not
	}

	public List<TargetStruct> TargetList = new List<TargetStruct>();//Your ICONS LIST
	public GameObject[] Targets;                                    //The GameObjects considered as targets

	private int targetsCount;                                       //Number of targets in the scene

	void Awake()                                                        
	{
		Targets = GameObject.FindGameObjectsWithTag("enemy");     //Get all the potential targets in the scene (just replace it by your own tag : "MyTag")
		foreach(GameObject target in Targets)                                   //Put every detected GameObject into your ICONS LIST
		{
			TargetStruct newTarget = new TargetStruct();
			newTarget.item = target;                                            //and attach each icon its GameObject
			TargetList.Add(newTarget);
		}
		
		targetsCount = TargetList.Count;                                        //Count the number of target in the scene
	}

	void Update()
	{       
		for(int i = 0; i<targetsCount; i++)                                                         //You have to repeat it for every icons : be aware that if you have too much that could use a lot of ressoures 
		{
			TargetStruct target = new TargetStruct();                                               //You have to create a temporary TargetStruct since you can't access a variable of an element in a list directly

			target = TargetList*;                                                                 //You take the item attached to the icon*

// if (target != null)
// {

  •  		target.screenPos = camera.WorldToScreenPoint(target.item.transform.position);           //Convert world coordinates of the item into screen ones*
    
  •  		target.distance = Vector3.Distance(target.item.transform.position, transform.position); //Get the distance between item and player*
    
  •  		if(target.distance>maxDistanceDisplay || target.distance<minDistanceDisplay)            //If the item is too far or too close*
    
  •  		{*
    
  •  			target.xTargetSize = minTargetIconSize;                                             //you want it to disappear*
    
  •  			target.yTargetSize = minTargetIconSize;                                             //or at least to be in its smaller size*
    
  •  		}*
    
  •  		else*
    
  •  		{*
    
  •  			target.xTargetSize = maxTargetIconSize/(target.distance);                           //Else you get its size with the*
    
  •  			target.yTargetSize = maxTargetIconSize/(target.distance);                           //distance : far<=>small / close<=>big*
    
  •  		}*
    
  •  		if(target.distance>maxDistanceDisplay)                                                  //If the item is too far, you set its screen position : (this way it seems as if the icon was coming away from the screen to focus your target)*
    
  •  		{*
    
  •  			if(target.screenPos.x<Screen.width/2)                                               //-if it's under the center of the view field*
    
  •  				target.xTargetPos = 0;                                                          //to the bottom of the screen*
    
  •  			else                                                                                //-else*
    
  •  				target.xTargetPos = Screen.width;                                               //to the top of the screen*
    
  •  			if(target.screenPos.y<Screen.height/2)                                              //-if it's on the right of the view field*
    
  •  				target.yTargetPos = Screen.height;                                              //to the right of the screen*
    
  •  			else                                                                                //-else*
    
  •  				target.yTargetPos = 0;                                                          //to the left of the screen*
    
  •  		}*
    
  •  		else                                                                                    //If the item is NOT too far, you set its screen position :*
    
  •  		{*
    
  •  			target.xTargetPos = target.screenPos.x-target.xSize/2;                              //in x-axis to the item's x-position minus half of the icon's size*
    
  •  			target.yTargetPos = Screen.height-target.screenPos.y-target.ySize/2;                //in y-axis to the item's y-position minus half of the icon's size*
    
  •  		}*
    

_ target.xSize = Mathf.Lerp(target.xSize, target.xTargetSize, smoothGrowingParameterTime.deltaTime); //You do lerps on your icons size so you can adjust_
_ target.ySize = Mathf.Lerp(target.xSize, target.yTargetSize, smoothGrowingParameter
Time.deltaTime); //the speed of their resizing_
_ target.xPos = Mathf.Lerp(target.xPos, target.xTargetPos, smoothMovingParameterTime.deltaTime); //You do lerps on your icons position so you can adjust_
_ target.yPos = Mathf.Lerp(target.yPos, target.yTargetPos, smoothMovingParameter
Time.deltaTime); //their moving speed_

  •  		RaycastHit hitInfos = new RaycastHit();                                                                 //You create a new variable to stock the information of the coming raycast*
    
  •  		Physics.Raycast(transform.position, target.item.transform.position-transform.position, out hitInfos);   //and you RayCast from the player's position to the item's position*
    
  •  		if(hitInfos.collider.gameObject.layer==8)                                                               //HERE IS A BIT TRICKY : you have to creat new layers (I called them "Interactive Items" and "Obstacles") and to apply them to your various items.*
    
  •  			target.directView=true;                                                                             //Then you select EVERY items in your scene and set their layer to "Ignore Raycast". After that you select your interactive items biggest shape (if you have big trigger colliders on them select the item that hold it),*
    
  •  		else                                                                                                    //and set their layers to "Interactive Items". Last part is setting every potential obstacle item layer to "Obstacles".*
    
  •  			target.directView=false;                                                                            //NOTE : Here my "Interactive Items" layer number is 8*
    

_ TargetList = target; //You apply all the variables to your index-i icon in the ICONS LIST_
// }
* }*
* }*

* void OnGUI()*
* {*
* for(int i = 0; i<targetsCount; i++) //For every icon*
* {*
if(TargetList_.screenPos.z>0 && (!directViewEnabled || (directViewEnabled && TargetList*.directView))) //If the icon is in front of you and all the required conditions are okay*
GUI.DrawTexture(new Rect(TargetList.xPos, TargetList.yPos, TargetList.xSize, TargetList*.ySize), targetIcon);//you display the icon with it’s size and position*
* }
}
}*_

the coment above by “Huacanacha” answered this for me, reposting as an answer so I can mark this as answered

TargetStruct is a struct, which can’t be null. The problem is that the item (GameObject) is probably being destroyed so references to target.item.transform are invalid. I can’t see where the objects are destroyed so I’m assuming that’s in an unrelated script.
Try adding Debug.Logs for target.item, and if that’s not null for target.item.transform. Then you will see what is actually failing.
Once you figure out what is going on you’ll need to maintain the target list when targets are destroyed. The easiest way would be to remove fro the list in Update() once an item is gone. You could also look into using a callback when the target objects are destroyed.