c# - Detect collision/colliding only once

Question

I have an object that moves towards another object and physically collides with it, I want that collision/colliding event to happen only once. I tried using a bool but it didn't work as intended. It seems that I'm doing something wrong.

bool doDamage = true;
void OnCollisionEnter2D(Collision2D other)
{
    if (other.gameObject.tag == "Target" && doDamage)
    {
        doDamage = false;
        // damage code
    }
}

void OnCollisionExit2D(Collision2D other)
{
    if (other.gameObject.tag == "Target")
    {
        doDamage = true;
    }
}

Edit:

I want the "damage code" to run only once, even if the 2 objects are still in contact. This script is only assigned to 1 object, not both.

Answer 1

I don't know the easiest way to explain why your code is not working but I will try.

You have two GameObjects:

1. GameObject A with doDamage variable.

2. GameObject B with doDamage variable.

When GameObject A collides with GameObject B:

A.The OnCollisionEnter2D function is called on GameObject A. if(other.gameObject.tag == "Target" && doDamage) executes because doDamage is true.

B.The doDamage variable from GameObject A is then set to false.

This does not affect the doDamage variable from GameObject B.

Then

C.The OnCollisionEnter2D function is called on GameObject B. if(other.gameObject.tag == "Target" && doDamage) executes because doDamage is true.

D.The doDamage variable from GameObject B is then set to false.

Both your damage code will run because doDamage is always true in each OnCollisionEnter2D call. What you are currently doing is only affecting doDamage variable in each individual script.

What you are currently doing:

Setting doDamage in the local/this script to false while also checking if local/this doDamage is set or not.

What you need to do:

Set doDamage in the other script to false but read the local/this doDamage to check if it is set or not.

This is what it should look like:

public class DamageStatus : MonoBehaviour
{
    bool detectedBefore = false;

    void OnCollisionEnter2D(Collision2D other)
    {
        if (other.gameObject.CompareTag("Target"))
        {
            //Exit if we have already done some damage
            if (detectedBefore)
            {
                return;
            }

            //Set the other detectedBefore variable to true
            DamageStatus dmStat = other.gameObject.GetComponent<DamageStatus>();
            if (dmStat)
            {
                dmStat.detectedBefore = true;
            }

            // Put damage/or code to run once below

        }
    }

    void OnCollisionExit2D(Collision2D other)
    {
        if (other.gameObject.tag == "Target")
        {
            //Reset on exit?
            detectedBefore = false;
        }
    }
}