CODEWITHSUNDEEP
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Daemonique
Daemonique

Reputation: 648

Updating image UI with unity

I was trying to make a program that updated the amount of hearts the player has every turn (full, half and empty hearts). When I was doing this I instantiated a gameobject of that prefab as a variable and then assigned it to my UI panel in unity. However (I'm not sure but I think that) the variables used in the update just before are still being referenced after being destroyed in the next loop giving me the error:

MissingReferenceException: The object of type 'GameObject' has been destroyed but you are still trying to access it.

Here is the update loop:

void Update()
{
    if (HP <= 0)
    {
        anim.SetBool("Death", true);
        Destroy(GameObject.Find("Hearts"));
        Destroy(GameObject.Find("Inventory"));
        text.alignment = TextAnchor.LowerCenter;
        text.text = "\n YOU DIED";
        text.fontSize = 150;
        text.color = new Color(255, 0, 0);
    } else {
        foreach (Transform child in GameObject.Find("Hearts").transform)
        {
            Destroy(child.gameObject);
        }
        for (var i = 0; i<(int)HP; i++)
        {
           GameObject Heart = Instantiate(heart, new Vector3(0, 0, 0), Quaternion.identity) as GameObject;
            Heart.transform.SetParent(GameObject.Find("Hearts").transform);
        }
        if (HP - (float)((int)HP) == 0.5F) {
            GameObject HalfHeart = Instantiate(halfheart, new Vector3(0, 0, 0), Quaternion.identity) as GameObject;
            HalfHeart.transform.SetParent(GameObject.Find("Hearts").transform);
        }
        for (var i =0; i<Mathf.Floor(MaxHP-HP); i++)
        {
            GameObject EmptyHeart = Instantiate(emptyheart, new Vector3(0, 0, 0), Quaternion.identity) as GameObject;
            EmptyHeart.transform.SetParent(GameObject.Find("Hearts").transform);
        }
    }

Is there a way to instantiate a prefab without making a variable?, or a way to make the variable reference temporary so it only lasts one update? Thank you for your help in advance!

Upvotes: 1

Views: 338

Answers (1)

Kalle Halvarsson
Kalle Halvarsson

Reputation: 1268

The problem is that once HP goes below zero, every subsequent update will enter the first if-statement and try to delete the "Hearts" and "Inventory" objects over and over. You can solve this by adding a bool called isDead and change the statement to if (HP <= 0 && !isDead) and then set isDead = true inside the block. This will prevent it from entering it twice.

Frankly though, your way of solving things is entirely backwards. As others have pointed out, deleting and instantiating objects every frame is very inefficient, and Transform.Find is also slow. You don't really need to destroy anything at all - you can rather just have a list of hearts and enable/disable an appropriate amount whenever the HP changes. You can have a single half-heart at the end of the list and enable/disable it when appropriate - if you are using a HorizontalLayoutGroup, it will still align correctly. You might want to make it so that you can only change the HP using a property or function (something like ModifyHealth(float amount)), and put the logic for updating the hearts display in there.

Upvotes: 2

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