How to change a single material at an object which has multiple materials.

Hello guys, I tried this script to swap a material of a game object on collision. Problem is that the collision happens correctly but the material is not swapped at all.

Code (CSharp):

1. using UnityEngine;
2. using System;
3.  
4. public class MaterialSwitcher : MonoBehaviour
5. {
6.     [SerializeField]
7.     int indexToSwitch = 0;
8.  
9.     [SerializeField]
10.     Material newMaterial;
11.  
12.  
13.     private Material GetMeshMaterialAtIndex(int index)
14.     {
15.         return GetComponent<Renderer>().materials[index];
16.     }
17.  
18.     public void SwitchMaterial()
19.     {
20.         Material currentMaterial = GetMeshMaterialAtIndex(indexToSwitch);
21.      
22.         Debug.Log("Collison worked!");
23.  
24.         if(String.Equals(currentMaterial.name, newMaterial.name))
25.         {
26.             Debug.Log("Material already swapped!");
27.         }
28.         else
29.         {
30.             GetComponent<Renderer>().materials[indexToSwitch] = newMaterial;
31.             Debug.Log("Material swapped succesfully!");
32.         }
33.     }
34. }
35.  

The function that should swap the material is called from another gameObject ( the player ) like so:

Code (CSharp):

1.  private void OnCollisionEnter(Collision other)
2.     {
3.          if(!other.gameObject.GetComponent<MaterialSwitcher>()) return;
4.          other.gameObject.GetComponent<MaterialSwitcher>().SwitchMaterial();
5.     }

And finally, this is the console output:


One funny thing is that If I create a public variable with an array of two materials, and I try to swap the current materials with the one in the array, it works! So the problem is with INDIVIDUAL material. If a game object has multiple materials, you can only change all of them or none at all.

Code (CSharp):

1. using UnityEngine;
2. using System;
3.  
4. public class MaterialSwitcher : MonoBehaviour
5. {
6.     [SerializeField]
7.     int indexToSwitch = 0;
8.  
9.     [SerializeField]
10.     Material newMaterial;
11.  
12.     [SerializeField]
13.     Material[] newMaterials;
14.  
15.     void Start()
16.     {
17.         // CHECK FOR ARRAY SWAP
18.         GetComponent<Renderer>().materials = newMaterials;
19.     }
20.    
21.     private Material GetMeshMaterialAtIndex(int index)
22.     {
23.         return GetComponent<Renderer>().materials[index];
24.     }
25.  
26.     public void SwitchMaterial()
27.     {
28.         Material currentMaterial = GetMeshMaterialAtIndex(indexToSwitch);
29.        
30.         Debug.Log("Collison worked!");
31.  
32.         if(String.Equals(currentMaterial.name, newMaterial.name))
33.         {
34.             Debug.Log("Material already swapped!");
35.         }
36.         else
37.         {
38.             GetComponent<Renderer>().materials[indexToSwitch] = newMaterial;
39.             Debug.Log("Material swapped succesfully!");
40.         }
41.     }
42. }
43.  

It is driving me nuts! Help guys!

Thank you for your time.

 

If you have a look at the docs here https://docs.unity3d.com/ScriptReference/Renderer-materials.html you'll see this line:

This means that the following line in your code is getting a new copy of the materials list, not a reference to the materials list on the object. When you swap the material it's only changing the new copy that you have.

GetComponent<Renderer>().materials[indexToSwitch] = new Material(newMaterial);

So the solution is to store a reference to the returned list, modify that reference, and then set it back to the renderer.

Code (CSharp):

1.         else
2.         {
3.             Material[] materials = GetComponent<Renderer>().materials;
4.             materials[indexToSwitch] = newMaterial;
5.             GetComponent<Renderer>().materials = materials;
6.             Debug.Log("Material swapped succesfully!");
7.         }

I would also recommend you store a Renderer varible in your MaterialSwitcher script that is set in Start() so that you only have to call GetComponent<> once.

 

Amazing! Thank you so much for your explanation, you right it works now and I understood why. Didn't know at all about this thing!