Help with damaging the enemy with cards

So, I started making a card game like Slay the Spire. I am pretty new to Unity, so I mostly do not know what I am doing. I made a card game object and an enemy. I also made the card draggable with mouse in game. I gave the enemy hp with using text mesh and I typed there something like ----. What I wanted them to do is that when I drag the card to the enemy one of the - would be reduced and the card will be destroyed. Instead, what they do is throwing me back to the scene (but the game still runs) and making me unable to move the card.

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

public class cardScript : MonoBehaviour
{

    bool canMove;
    bool dragging;

    Collider2D collider;

    private void Start()
    {
        collider = GetComponent<Collider2D>();
        canMove = false;
        dragging = false;
    }

    private void Update()
    {
        Vector2 mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        if (Input.GetMouseButtonDown(0))
        {
            if (collider == Physics2D.OverlapPoint(mousePos))
            {
                canMove = true;
            }

            else
            {
                canMove= false;
            }

            if (canMove)
            {
                dragging = true;
            }

        }
        if (dragging)
        {
            this.transform.position = mousePos;
        }
        if (Input.GetMouseButtonUp(0))
        {
            canMove = false;
            dragging = false;
        }

    }

    private void OnTriggerEnter2D(Collider2D co)
    {
        if (co.name == "enemy")
        {
            co.GetComponentInChildren<Health>().decrease();
            Destroy(gameObject);
        }
    }

}

this is the code for the card

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

public class Health : MonoBehaviour
{
    TextMesh tm;
   
    void Start()
    {
        tm = GetComponent<TextMesh>();
    }

    public int current()
    {
        return tm.text.Length;
    }

    public void decrease()
    {
        if (current() > 1)
            tm.text = tm.text.Remove(tm.text.Length - 1);
        else
            Destroy(transform.parent.gameObject);
    }
}

And this is the code for enemy hp.
Help

Sounds like a bug! Time to start debugging. Before you do, contrive the simplest example of cards required to show the problem, even if you hard-place a few cards on the table to start, then go try your problematic code. This will let you quickly iterate and learn what the code is doing.

You must find a way to get the information you need in order to reason about what the problem is.

What is often happening in these cases is one of the following:

  • the code you think is executing is not actually executing at all
  • the code is executing far EARLIER or LATER than you think
  • the code is executing far LESS OFTEN than you think
  • the code is executing far MORE OFTEN than you think
  • the code is executing on another GameObject than you think it is
  • you’re getting an error or warning and you haven’t noticed it in the console window

To help gain more insight into your problem, I recommend liberally sprinkling Debug.Log() statements through your code to display information in realtime.

Doing this should help you answer these types of questions:

  • is this code even running? which parts are running? how often does it run? what order does it run in?
  • what are the values of the variables involved? Are they initialized? Are the values reasonable?
  • are you meeting ALL the requirements to receive callbacks such as triggers / colliders (review the documentation)

Knowing this information will help you reason about the behavior you are seeing.

You can also supply a second argument to Debug.Log() and when you click the message, it will highlight the object in scene, such as Debug.Log("Problem!",this);

If your problem would benefit from in-scene or in-game visualization, Debug.DrawRay() or Debug.DrawLine() can help you visualize things like rays (used in raycasting) or distances.

You can also call Debug.Break() to pause the Editor when certain interesting pieces of code run, and then study the scene manually, looking for all the parts, where they are, what scripts are on them, etc.

You can also call GameObject.CreatePrimitive() to emplace debug-marker-ish objects in the scene at runtime.

You could also just display various important quantities in UI Text elements to watch them change as you play the game.

If you are running a mobile device you can also view the console output. Google for how on your particular mobile target, such as this answer or iOS: https://discussions.unity.com/t/700551 or this answer for Android: https://discussions.unity.com/t/699654

Another useful approach is to temporarily strip out everything besides what is necessary to prove your issue. This can simplify and isolate compounding effects of other items in your scene or prefab.

Here’s an example of putting in a laser-focused Debug.Log() and how that can save you a TON of time wallowing around speculating what might be going wrong:

https://discussions.unity.com/t/839300/3

When in doubt, print it out!™

Note: the print() function is an alias for Debug.Log() provided by the MonoBehaviour class.

I somehow solved throwing back to the scene thing I do not know how. And I guess I also had to tell what errors I was getting from console. Thats on me. And it looks like looks like it wasn’t working because enemy did not have the text mesh instead, I had made another game object inside enemy that I named Health and that was where text mesh was. I made Health’s own collider and used that one in the code and then it worked.