How do I use a function’s return value as a parameter in another function?

Question

I am using Unity 2019.4.20f1

Hi, I am currently trying to dynamically set the Game Object value of a button’s OnClick() method. To do this, I am trying to use a delegate event system, which passes along a reference to the clicked-on-GameObject and a couple of functions.

alt text

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 // Attatched to InspectMenuController GameObject
 public class InspectMenuController : MonoBehaviour
 {
     private Transform equipTransform;
     private GameObject currentPrefab;
 
     public GameObject useButton;
     public GameObject replaceButton;
 
     private void OnEnable()
     {
         GameEvents.OnMessageSent += SetCurrentPrefab;
     }
     private void OnDisable()
     {
         GameEvents.OnMessageSent -= SetCurrentPrefab;
     }
    
     // This method is called after a GameObject has been clicked on
     // I think it should take the clicked on GameObject reference as a parameter
     // I don't think it is set up correctly
     public void SetCurrentPrefab(GameObject myClickedPrefab)
     {
         GetCurrentPrefab(myClickedPrefab);
     }
 
     // When this function is called by SetCurrentPrefab it should retrun the passed in GameObject parameter as a value
     // I don't think it is set up correctly
     public GameObject GetCurrentPrefab(GameObject myClickedPrefab)
     {
         myClickedPrefab = currentPrefab;
         Debug.Log("Made it to GetCurrentPrefab");
         return currentPrefab;
     }
 
     // This function should be called with a button OnClick method
     // Ideally, it would use the GetCurrentPrefab return value to dynamically set the GameObject value in the OnClick method
     // I don't think it is set up correctly
     public void CenterPrefab(GameObject currentPrefab)
     {
         currentPrefab = GetCurrentPrefab(currentPrefab);
         if (currentPrefab.TryGetComponent(out EquipmentClass equipment))
         {
             // currentPrefab = myClickedPrefab;
             Debug.Log(equipment.Name);
             Debug.Log("Hi CurrentPrefab");
         }
     }
 }

My project is set up in a way that everytime a GameObject is clicked, it triggers a delegate event which passes on a reference to the clicked-on-gameObject to all of the event subscribers. When the delegate event is triggered it calls the function SetCurrentPrefab(GameObject myClickedPrefab). I am using this function mainly to call the next function GetCurrentPrefab(GameObject, myClickedPrefab). Both methods’ arguments should be filled by the currently selected GameObject. However, as I type this I am realizing that I probably don’t have this set up correctly. GetCurrentPrefab() would then return a GameObject as a value, and that GameObject should be the GameObject which was passed along with the delegate event.

Finally, CenterPrefab(GameObject currentPrefab) should pass in GetCurrentPrefab()’s return value as a parameter for its currentPrefab argument. I am using the out parameter to access the selected-GameObject’s components.

As it is currently set up, I am given the error: ArgumentException: Object of type 'UnityEngine.Object' cannot be converted to type 'UnityEngine.GameObject'

When I manually set the OnClick() parameter to the GameObject I am currently testing on I get the error: NullReferenceException: Object reference not set to an instance of an object. This error is triggered by line 45, and I think it has something to do with how I’m using the out parameter and the fact that I am probably not passing my GameObject correctly between the previous three functions.

I’m not sure if this is useful but, in the dropdown menu, I only have one option, CenterPrefab( GameObject), rather than the usual two, static and dynamic.

I’m not a competent coder, and there is a good chance a lot of this is nonsense as I’m not always sure if I am correctly using terms and what-not. I would be very thankful for any help!

Answer 1

Best Answer

Answer by rage_co · Jul 27, 2021 at 04:09 AM

Ah! I just paid attention to what you said in the paras after the code (i was late last night, sorry i didn't pay more attention then)...so the first solution i suggested is wrong, you can roll it back, keep the variable names solution tho, since i didn't understand the jist of the problem, the error lies in the fact that you cannot call a function without providing the adequate parameters.

The correct approach would be to use another parameterless function to call the CenterPrefab() function

 public void CallCP()
 {
   GameObject prefabReturn = GetCurrentPrefab();
   CenterPrefab(prefabReturn);
 }

and remove the

 currentPrefab = GetCurrentPrefab(currentPrefab);

line from CenterPrefab() altogether. Also you need to remove the GameObject parameter from the GetCurrentPrefab function, instead just replace it's contents entirely with

 {
   Debug.Log("");
   return(currentPrefab);
 }

Also SetCurrentPrefab is kind of both useless since it only calls GetCurrentPrefab with the same parameter and i don't think it does the job it's intended to...so to correct it

 public void SetCurrentPrefab(GameObject myClickedPrefab)
 {
    currentPrefab = myClickedPrefab;
 }

and pass the myClickedPrefab parameter through the inspector (seeing that you aren't using raycasts directly on objects and instead buttons to do the trick).....and i think this should do....Hope this helps!

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wattse13 · Jul 27, 2021 at 08:29 AM 1

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It works! In addition to your suggestions, I had to declare prefabReturn as a GameObject variable. After that I took the empty GameObject that the InspectMenuController script was attatched to and added it to the OnClick() method through the inspector. Thank you for your time and help! How can I mark you answer as correct? Edit: It also works when prefabReturn is replaced with currentPrefab.

rage_co wattse13 · Jul 27, 2021 at 09:06 AM 0

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Oops, sorry about not declaring prefabReturn as an GameObject, i wrote the code right here..soo i couldn't check for errors...i will edit that into the comment and convert it into an answer...then you can accept it...again, glad that i could be of service.

How do I use a function’s return value as a parameter in another function?

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