Question Detecting existing colliders in 2D

Hello!
I am kind of new at Unity, so I hope my question will seem simple and easy to solve.

I am playing around with the engine. Currently I have a small field and a UI with one button for spawning a prefab. When I click the button it spawns the prefab on top of the mouse and then after a left click it places it in the world.

I add a 2D box collider to the prefab, but when I use OnMouseEnter to check for collisions, it does not register at all.

This is the code for the button which spawns the prefab.

Code (CSharp):

1. public class SpawnBuilding : MonoBehaviour
2. {
3.  
4.     //Mudhut and coordinates for it
5.     public GameObject mudHut;
6.     public Vector3 coordinates;
7.  
8.     void Start()
9.     {
10.  
11.     }
12.  
13.     // Update is called once per frame
14.     void Update()
15.     {
16.  
17. }
18.  
19.     public void Build() {
20.  
21.         coordinates = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 7);
22.         Instantiate(mudHut, coordinates, Quaternion.identity);
23.     }
24.  
25. }
26.  

This is the code attached to the prefab which allows to move and place it.

Code (CSharp):

1. public class PlaceBuilding : MonoBehaviour
2. {
3.     //Used for mouse coordinates
4.     float x;
5.     float y;
6.  
7.     //Used to detect collision with another building
8.     private bool noCollision;
9.  
10.     // Start is called before the first frame update
11.     void Start()
12.     {
13.         noCollision = true;
14.     }
15.  
16.     // Update is called once per frame
17.     void Update()
18.     {
19.  
20.         x = Input.mousePosition.x;
21.         y = Input.mousePosition.y;
22.  
23.         transform.position = Camera.main.ScreenToWorldPoint(new Vector3(x, y, 7));
24.        
25.         //Left click to place the prefab
26.         if (Input.GetMouseButtonDown(0) && noCollision)
27.         {
28.             Cursor.visible = true;
29.             gameObject.AddComponent<BoxCollider2D>();
30.             Destroy(this);
31.         }
32.         //Right click to destroy the prefab
33.         else if (Input.GetMouseButtonDown(1))
34.         {
35.             Cursor.visible = true;
36.             Destroy(gameObject);
37.             Destroy(this);
38.         }
39.     }
40.    
41.     //Enter collider
42.     private void OnMouseEnter()
43.     {
44.         noCollision = false;
45.     }
46.  
47.     //Exit collider
48.     private void OnMouseExit()
49.     {
50.         noCollision = true;
51.     }
52. }
53.  

This method of doing it I saw in a book called "Getting Started with Unity 5.x 2D Game Development". There you make a simple tower defense and the code works. But for some reason, it does not work for me here.

 

The problem has been fixed by using Rays to detect the presence of a collider on the screen, instead of relying on OnMouseEnter() to detect a collision.