cached and refactored a bit

problem : spelling errors and lisibility issues with some parts of the code

solution :

- used GetAllComponents generic nature to eliminate the need for casting
- cached sprite renderers in the Placeholder
- put hardcoded string in a const variable

Assets/Scripts/Drag&Drop/DraggablePlaceholder.cs

@@ -4,6 +4,8 @@ using UnityEngine;
 
 public abstract class DraggablePlaceholder : MonoBehaviour
 {
+    protected const string OutlineColor = "_OutlineColor";
+
     [SerializeField]
     protected Color _validColor = Color.green;
     [SerializeField]
@@ -13,6 +15,12 @@ public abstract class DraggablePlaceholder : MonoBehaviour
     protected Rect _lvlBoundsCache;
     protected bool _isOnValidPosition;
 
+    private List<SpriteRenderer> _outlineRenderers = new List<SpriteRenderer>();
+    public List<SpriteRenderer> OutlineRenderers
+    {
+        get => _outlineRenderers;
+    }
+    
     /// <summary>
     /// calculate level boundaries and finds main camera.
     /// </summary>
@@ -79,10 +87,9 @@ public abstract class DraggablePlaceholder : MonoBehaviour
     {
         Color getColor() => _isOnValidPosition ? _validColor : _invalidColor;
 
-        foreach (var child in GetComponentsInChildren<SpriteRenderer>(true))
+        foreach (var child in _outlineRenderers)
         {
-            if (!child.material.HasProperty("_OutlineColor")) continue;
+            child.material.SetColor(OutlineColor, getColor());
-            child.material.SetColor("_OutlineColor", getColor());
         }
     }
     public abstract void Place();

Assets/Scripts/Drag&Drop/GameObjectPlacementButton.cs

@@ -1,4 +1,5 @@
-using UnityEngine;
+using System.Linq;
+using UnityEngine;
 
 public class GameObjectPlacementButton : UnitPlacementButton
 {
@@ -18,19 +19,22 @@ public class GameObjectPlacementButton : UnitPlacementButton
         foreach (var coll in instance.transform.GetAllComponents<Collider2D>()) Destroy(coll);
         foreach (var script in instance.transform.GetAllComponents<MonoBehaviour>()) Destroy(script);
 
-        //assign outline material tou all renderers of the placeholder
+        var placeholder = instance.AddComponent<ObjectPlaceholder>();
+        placeholder.Prefab = _prefab;
+
+        //assign outline material to all renderers of the placeholder
         foreach (var rend in instance.transform.GetAllComponents<SpriteRenderer>())
         {
-            var color = (rend as SpriteRenderer).color;
-            color.a = 0.6f;
-            (rend as SpriteRenderer).color = color;
             
-            (rend as SpriteRenderer).material = _outlineMaterial;
+            var color = rend.color;
+            color.a = 0.6f;
+            rend.color = color;
+
+            rend.material = _outlineMaterial;
+            placeholder.OutlineRenderers.Add(rend);
         }
         
 
-        var placeholder = instance.AddComponent<ObjectPlaceholder>();
-        placeholder.Prefab = _prefab;
 
         CreateRange(placeholder, detectionRect);
     }

Assets/Scripts/General/Extensions.cs

@@ -7,7 +7,7 @@ using GatherAndDefend.LevelEditor;
 
 public static class Extensions
 {
-    public static Component[] GetAllComponents<T>(this Component component) where T : Component
+    public static T[] GetAllComponents<T>(this Component component) where T : Component
     {
         List<T> comps = new List<T>();
         comps.AddRange(component.GetComponents<T>());