Unity Destroy 和其他代码不起作用？

Question

I'm trying to make the game Snake, and I'm trying to get the apple functionality working. What this script is meant to do, is whenever my Snake goes over the Apple, the apple disappears and reappears at a random location on the screen. But instead it does nothing, any idea as to why?

PS: Camera is Size 10 and Aspect Ratio is 16:9 which is why I have some weird Random.Range values. Also I used Debug.Log in Update to make sure that the variable worked, and yes it does, whenever my snake moves its coordinates are displayed.

public class Apple_RandomSpawn : MonoBehaviour
{
    private Vector2 foodPos;
    private Snake_Move snakeMove;

    void Start()
    {
        SpawnApple();
    }

    public void Update()
    {
        transform.position = new Vector2(foodPos.x, foodPos.y);
        SnakeAte();
    }

    public void SpawnApple()
    {
        foodPos = new Vector2(Random.Range(-17, 17), Random.Range(-9, 9));
    }

    public void SnakeAte()
    {
        if (Mathf.Approximately(foodPos.x, snakeMove.pos.x) && Mathf.Approximately(foodPos.y, snakeMove.pos.y))
        {
            SpawnApple();
        }
    }
}

Answer 1

First of all, it does not directly have something to do with your problem, but DO NOT put GetComponent() or GameObject.Find() in the Update() function. These two, especially GameObject.Find() function is super heavy , so It's recommended that you should call these kinds of function inside Start() or Awake() , or at the initiallization of a class. It can directly, and heavily impact the performance of your game, so here's my suggestion:

[SerializeField]
private Snake_Move snakeMove;

And drag your gameobject (which Snake_Head component is attatched) via Inspector. You should always consider this way first, rather than using GameObject.Find() and GetComponent() .

Second, Float is not recommend to compare equality directly through = , since there must be rounding error . There is a help function with regard to comparing two float value in Unity, like Mathf.Approximately(float a, float b) . Directly comparing two float value via = would almost always not work as you might think.

Third, It doesn't seem to be that there are no Instantiate() function in your code, but you are try to use one apple object, and every time you consume it, just change it's position. Then why does Object.Destroy(gameObject) exists? What you're doing is, just destroying the apple when you get it first time. I think you have to remove the Destroy() function, and SpawnApple() changes the target coordinate of apple, and the position will be updated in Update() function.

And it's no need to indirectly set the target position, and update to it in Update() function. You can directly set the position of apple, like:

// assuming you followed my suggestio aboven about snakeMove.

public void Update()
    {
        SnakeAte();

        Debug.Log(snakeMove.pos);
    }

public void SpawnApple()
    {
        transform.position = new Vector2(Random.Range(-17, 17), Random.Range(-9, 9));
    }

public void SnakeAte()
    {
        if (foodPos == snakeMove.pos)
        {
            SpawnApple();
        }
    }

Answer 2

First of all your null ref in your last comment comes from: private Snake_Move snakeMove; Its a private variable and its never assigned. You either need to make it public/[SerialistField] and assign it in inspect or have some sort of initialize function that give it a value.

For the hit detection Mathf.Approximately is good if you wan to check if 2 floats are exactly the same. If you'r checking 2 positions of moving objects the chance of them being exactly the same is very low and may rely on frame rate and such. Keeping your implementation you can check instead for a minimum distance between the 2 positions. You can tweak DISTANCE_THRESHOLD for a value that suits your better.

public class Apple_RandomSpawn : MonoBehaviour
        {
            private const float DISTANCE_THRESHOLD = 0.1f;
            private Vector2 foodPos;
            private Snake_Move snakeMove;

            void Start()
            {
                SpawnApple();
            }

            public void Update()
            {                   
                SnakeAte();
            }

            public void SpawnApple()
            {
                foodPos = new Vector2(Random.Range(-17, 17), Random.Range(-9, 9));
                transform.position = new Vector2(foodPos.x, foodPos.y);
            }

            public void SnakeAte()
            {
                if (Vector3.Distance(foodPos, snakeMove) < DISTANCE_THRESHOLD)
                {
                    SpawnApple();
                }
            }
        }

Now remember that since your teleporting the apple to a purely random location it might teleport right back on top of your snake:).