How can I detect how many gameobjects have a certain material?

Question

So I'm currently working on a puzzle game in unity using c#. The way I'm determining whether the player won or not is if a bunch of gameobjects have the same material. How can I determine how many gameobjects have a certain material attached?

Answer 1

This code should help you.

When you call this method passing the Material you want to check, it gives back the number of GameObjects, currently active in scene, that use the same Material.

    //-----------------------------------------------------------------------------
    // getObjsWithMat
    //-----------------------------------------------------------------------------
    public static int getObjsWithMat (Material mat) {
        Material m_DefaultMat = mat;
        int m_c = 0;

        GameObject[] AllObjs = Object.FindObjectsOfType<GameObject> ();
        foreach (GameObject Obj in AllObjs) {
            if (Obj.activeInHierarchy) {
                if (Obj.GetComponent <Renderer> ()) {
                    foreach (Material Mat in Obj.GetComponent <Renderer> ().sharedMaterials) {
                        if (Mat == m_DefaultMat)
                            m_c++;
                    }
                }
            }
        }

        return m_c;
    }

This is the implementation I did in the editor to test it out. Since I made it and I don't need it, I figured it could help someone sometime, so here it is. You need to copy it in a script preferably called 'GetStatsWindow.cs', that must be in a folder called 'Editor'. You can open the window in the edito from the menu "Window/Find Objects with Material".

//---------------------
//FrankGames production
//---------------------

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;

public class GetStatsWindow : EditorWindow {

    private static Material m_DefaultMat = null;
    private static int m_c = -1;
    private static int m_c2 = 0;

    private static bool m_DisplayResult = false;
    private static Vector2 m_RectPos = Vector2.zero;

    private static GameObject[] m_ObjsFound = new GameObject[0];

    private static bool m_Working = false;

    //-----------------------------------------------------------------------------
    // ShowWindow
    //-----------------------------------------------------------------------------
    [MenuItem ("Window/Find Objects with Material")]
    public static void ShowWindow () {
        EditorWindow.GetWindow (typeof (GetStatsWindow));
    }

    //-----------------------------------------------------------------------------
    // OnGUI
    //-----------------------------------------------------------------------------
    void OnGUI () {
        EditorGUILayout.BeginVertical ();

        EditorGUILayout.HelpBox ("First, select a material in the 'Material to find' Input field.\nThan press the 'Find' Button.\nAfter some calculations (it could take some time, depending on your Hardware and the amount of objects and Materials that it has to check.", MessageType.Info);

        if (m_Working)
            EditorGUI.BeginDisabledGroup (true);

        m_DefaultMat = EditorGUILayout.ObjectField ("Material to find", m_DefaultMat, typeof (Material), true) as Material;

        if (m_DefaultMat == null && !m_Working)
            EditorGUI.BeginDisabledGroup (true);

        if (GUILayout.Button ("Find Objects")) {
            getObjWithMat ();
        }

        if (m_DefaultMat == null && !m_Working)
            EditorGUI.EndDisabledGroup ();

        if (m_Working)
            EditorGUILayout.LabelField ("Calculating...");

        if (m_c != -1) {
            if (GUILayout.Button ("Clear result") && EditorUtility.DisplayDialog ("Are you sure?", "Do you really want to clear the result of your search?", "Continue", "Cancel")) {
                m_DefaultMat = null;
                m_c = -1;
                m_c2 = 0;
                m_DisplayResult = false;
                m_RectPos = Vector2.zero;
                m_ObjsFound = new GameObject[0];
                m_Working = false;
            } else {

                EditorGUILayout.LabelField (m_c2 + " Objects have been checked!");
                EditorGUILayout.LabelField (m_c + " Objects with the '" + m_DefaultMat.name + "' Material have been found!");

                m_DisplayResult = EditorGUILayout.Toggle ("Display Results", m_DisplayResult);

                if (m_DisplayResult) {
                    EditorGUILayout.LabelField ("Objects found with '" + m_DefaultMat.name + "':");

                    m_RectPos = EditorGUILayout.BeginScrollView (m_RectPos);
                    EditorGUILayout.BeginVertical ();
                    EditorGUI.BeginDisabledGroup (true);
                    for (int i = 0; i < m_ObjsFound.Length; i++) {
                        EditorGUILayout.ObjectField ("[" + i + "] Object found", m_ObjsFound [i], typeof(GameObject), true);
                    }
                    EditorGUI.EndDisabledGroup ();
                    EditorGUILayout.EndVertical ();
                    EditorGUILayout.EndScrollView ();

                }
            }
        }

        if (m_Working)
            EditorGUI.EndDisabledGroup ();

        EditorGUILayout.EndVertical ();
    }

    //-----------------------------------------------------------------------------
    // getObjWithMat
    //-----------------------------------------------------------------------------
    public static int getObjWithMat (Material mat = null) {
        if (mat != null)
            m_DefaultMat = mat;
        else if (m_DefaultMat == null)
            return -1;

        m_Working = true;

        m_c = 0;
        m_c2 = 0;

        List<GameObject> Objs = new List<GameObject> ();

        GameObject[] AllObjs = Object.FindObjectsOfType<GameObject> ();
        foreach (GameObject Obj in AllObjs) {
            m_c2++;
            bool Found = false;
            if (Obj.activeInHierarchy) {
                if (Obj.GetComponent <Renderer> ()) {
                    foreach (Material Mat in Obj.GetComponent <Renderer> ().sharedMaterials) {
                        if (Mat == m_DefaultMat) {
                            Found = true;
                            m_c++;
                        }
                    }
                }
            }
            if (Found)
                Objs.Add (Obj);
        }

        m_ObjsFound = Objs.ToArray ();
        Objs.Clear ();

        m_Working = false;

        return m_c;
    }

}

[Edit] I saw the code example that you shared, used to change the material.

Try instead:

if (col.GetComponent<MeshRenderer> ())
    col.GetComponent<MeshRenderer> ().sharedMaterial = mat;

This is because checking if the GameObject has the component before accessing it, even if it might not be necessary for your solution, it can prevent some 'Null Exception reference' from happening. Also, using .sharedMaterial is a safer option that using the .material, as it creates a new instance of the material (I corrected this last affermation from the answer of @fredrik-widerberg because I was incorrect). The last tip, if you didn't know, getting the Renderer component, allows you to get access to all Renderer types (such as MeshRenderer, SkinnedMeshRenderer, ...).

I hope I was Helpful!

Diego