Why NullReferenceException when nothing is null?

Question

Here is my code:

 protected void TerrainOn(Transform clop)
     {
         MediumTank tank = currentUnit;
         Collider[] colliderList = Physics.OverlapSphere(clop.position, 0.5f);
         if (colliderList.Length != 0)
         {
 
             switch (colliderList[0].tag)
             {
                 case "town":
                     GameObject townhexon = GameObject.Find("townHex");
                     tank.CurrentDefence = tank.InitialDefence + townhexon.GetComponent<Town>().town.VehDefence;
                     break;
 
                 case "plains":
                     GameObject plainsHexOn = GameObject.Find("plainsHex");
                     tank.CurrentDefence = tank.InitialDefence + plainsHexOn.GetComponent<Plains>().plains.VehDefence;
 
                     break;
             }
         }
     }

Unity throws a null reference exception saying that clop is not set to an instance of an object on line 4 when I try to execute TerrainOn(), but clop is definitely set to a valid transform in the inspector.

Answer 1

Answer by Captain_Pineapple · Jul 20, 2022 at 09:16 AM

This is not how you should approach this. If you can set clop in the inspector this means it is a member variable a la

 public class SomeClass {
       public Transform clop; //member variable
       
       public void TerrainOn(Transform clop) //clop is local variable
       {
              Debug.Log(this.clop); // member variable
              Debug.Log(clop); //clop is local variable
       }
 }

also just because you assign somethin in the editor does not mean that the code could not overwrite the value somewhere.

So if you want to claim that "nullref even though variable is not null" then please prove this by adding a Debug.Log(clop); in line 3.

0 Show 5 · Share

TheQwertz · Jul 22, 2022 at 08:41 AM 0

Share

Hi, sorry for ignoring this answer. I couldn't find this question when I went to look for it so I assumed it was deleted, hence the duplicate question. Debug.Log(clop) gives the transform that I assigned in the inspector. I have double checked everything and cannot find the problem anywhere.

Captain_Pineapple TheQwertz · Jul 22, 2022 at 08:52 AM 0

Share

sure no problem.

Problem here is: if

  Debug.Log(clop);

does not say null then it is quite unlikely (to a level of impossibility) that it randomly becomes null in the next line.

Try this:

 Debug.Log("called on Object: " + gameObject.name);
 Debug.Log("clop is: " + clop);
 Debug.Log("clop position: " + clop.position);
 Debug.Log("tests done");
 Collider[] colliderList = Physics.OverlapSphere(clop.position, 0.5f);

If this runs then you really should check if you did not mix up the line your nullref points to. If you want to be really sure i'd suggest you learn how to attach the visual studio debugger to your unity instance so you can set a breakpoint in the code and step through the code line by line.

TheQwertz Captain_Pineapple · Jul 22, 2022 at 10:13 AM 0

Share

I could have sworn it was line 4. . . Now the nre is line 17, so that means either tank.InitialDefence or plains.VehDefence is null?

Show more comments

Why NullReferenceException when nothing is null?

1 Reply

Your answer

Welcome to Unity Answers

Follow this Question

Related Questions