Tukukkk

Let's suppose we have two cylinders in the scenes with red and blue materials on them. Also, we have two UI images with red and blue background. Now, what should I do to make the red image only draggable onto red cylinder and the blue image only draggable onto blue cylinder.

If I drag the red image onto the blue cylinder, then an error message should appear:

same for dragging blue image on red cylinder or vice versa.

See the picture below

using System.Collections;

using System.Collections.Generic;

using UnityEngine;



public class wrench : MonoBehaviour {



    public bool Dragging = false;

    public bool collision = false;

    Vector3 position;

    public List<GameObject> UIimages;



    public void BeginDrag() {



        position = gameObject.transform.position;

        Dragging = true;

        foreach (GameObject obj in UIimages) {

            obj.GetComponent<BoxCollider2D> ().enabled = false;

        }

    }



    public void Drag() {

        transform.position = Input.mousePosition;

    }



    public void Drop() {

        if (!collision) {

            gameObject.transform.position = position;

        }

        Dragging = false;

    }

}

Assuming your dropps are already detected as you say and the question is more about how to differ between the objects I would use a simple enum e.g.

public enum WhichObject

{

    red,

    blue

}

the advantage is that later you can very easily add more options without having to deal with layers, tags etc.

On the GameObject you drag around add a component e.g.

public class ObjectInformation

{

    public WhichObject IsObject;

}

and simply select in the Inspector (or if you spawn them via script) for each of your dragged objects which value the WhichObject variable shall have.

Than on your target objects where you detect the collision also add a WhichObject variable but this time configure the value you expect to be dropped here

public WhichObject ExpectedObject;

again set it via the inspector or script.

Than simply add a check

var info = droppedObject.GetComponent<ObjectInformation>();



// Something else dropped?

if(!info) return;



// Now check if the value matches

// the one this object expects

if(info.IsObject == ExpectedObject)

{

    // Correct object

    Debug.Log("Yeah!");

} 

else 

{

    // Wrong object

    Debug.LogFormat("Dropped object {0} does not match the expected object {1}!", info.IsObject, ExpectedObject);

}

Later you can also simply extend it using multiple enums like e.g. colors, forms etc.

And maybe you could as well make the check the other way round and check on the dragged object, if the values match and if the don't match not even allow to be dropped on that target object (this depends of course on your implementation).