How to spawn prefabs within a certain period of time in Unity?

Question

I am trying to create a ball hitting game in the baseball format. I create a ball as a prefab. I want to push the ball to the main scene within a certain period of time.

For example; when the first ball is in the scene, the second ball will spawn after 5-6 seconds, then the third, fourth etc. I am the beginner level of Unity and I am not good at C#. I am not sure whether I am using the true functions such as Instantiate. Here is my script:

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

public class Ball : MonoBehaviour {
    public float RotateSpeed = 45; //The ball rotates around its own axis
    public float BallSpeed = 0.2f; 

    public GameObject[] prefab;

    public Rigidbody2D rb2D;

    void Start() {
        rb2D = GetComponent<Rigidbody2D>(); //Get component attached to gameobject
        Spawn ();
    }

    void FixedUpdate() {
        rb2D.MoveRotation(rb2D.rotation + RotateSpeed * Time.fixedDeltaTime); //The ball rotates around its own axis
        rb2D.AddForce(Vector2.left * BallSpeed);
        InvokeRepeating("Spawn", 2.0f, 2.0f);

    }

    public void Spawn () 
    {
        int prefab_num = Random.Range(0,3);
        Instantiate(prefab[prefab_num]);
    }

}

After I apply this script, the result is not what I want.

score 3 · Answer 1 · edited May 29 '18 at 00:26

3

Add InvokeRepeating("Spawn", 2.0f, 2.0f); to the Start not the FixedUpdate. InvokeRepeating invokes the method methodName in time seconds, then repeatedly every repeatRate seconds. You can check the documentation here.

edited May 29 '18 at 00:26

ThePyzhov

259
2
14

answered May 28 '18 at 20:56

WaleedYaser

605
5
9

score 3 · Answer 2 · edited Jun 20 '20 at 09:12

3

Use Coroutines

private IEnumerator SpawnBall() {
    while(true) {
        Instantiate(baseball);
        yield return new WaitForSeconds(5);
    }
}

Which can then be started with StartCoroutine() and terminated in one of three ways:

internally by breaking out of the while loop with break (the function would then have no more lines to execute and exit)
internally by yield break
externally by calling StopCoroutine() on a reference to the coroutine

edited Jun 20 '20 at 09:12

Community

1
1

answered May 29 '18 at 01:20

Draco18s no longer trusts SE

15,628
3
36
56

How can I use coroutine with prefab? When I want to update the code, it gives an error: `The type UnityEngine.GameObject[] cannot be used as type parameter T in the generic type or method UnityEngine.Object.Instantiate(T). There is no implicit reference conversion from UnityEngine.GameObject[] to UnityEngine.O` @Draco18s – Katzenliebe May 29 '18 at 15:23
1

Prefabs have nothing to do with your problem, but rather that you're trying to pass *an array* to a function that does not take an array. – Draco18s no longer trusts SE May 29 '18 at 18:57

score 2 · Answer 3 · answered May 29 '18 at 16:38

2

Alternative to the other answers: Just use a countdown. This sometimes gives you more control

// Set your offset here (in seconds)
float timeoutDuration = 2;

float timeout = 2;

void Update()
{
    if(timeout > 0)
    {
        // Reduces the timeout by the time passed since the last frame
        timeout -= Time.deltaTime;

        // return to not execute any code after that
        return;
    }

    // this is reached when timeout gets <= 0

    // Spawn object once
    Spawn();

    // Reset timer
    timeout = timeoutDuration;
}

answered May 29 '18 at 16:38

derHugo

83,094
9
75
115

Thank you. But I still can't achieve the expected result: https://i.imgur.com/c2TA5ZF.gif It's really hard to understand the issue for me. – Katzenliebe May 30 '18 at 14:54
I don't really get what you are doing or trying to archive to be honest. I wouldn't put this update function in the ball itself but on a seperated static gameoject. Right now it seems to be exponential because: you spawn a new ball every 2 seconds BUT: this newly spawned ball as well spawns a new ball every 2 seconds => after 2 seconds you have 2 balls, after 4 seconds both spawn a new ball => 4 balls; again after 2 seconds every of those spawn a new ball => 8 balls .... – derHugo May 31 '18 at 18:14

score 0 · Answer 4 · answered Jun 05 '18 at 17:27

I updated my script by considering your feedbacks and it works like a charm. Thanks to all!

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using System.Threading;

public class Ball : MonoBehaviour {
    public float RotateSpeed = 45; //The ball rotates around its own axis
    public float BallSpeed = 0.2f; 

    public GameObject BaseBall;
    public Transform BallLocation;

    public Rigidbody2D Ball2D;

    void Start() {
        Ball2D = GetComponent<Rigidbody2D>(); //Get component attached to gameobject
        InvokeRepeating("Spawn", 5.0f, 150f);
    }       

    void FixedUpdate() {
        Ball2D.MoveRotation(Ball2D.rotation + RotateSpeed * Time.fixedDeltaTime); //The ball rotates around its own axis
        Ball2D.AddForce(Vector2.left * BallSpeed);
    }

    public void Spawn () 
    {
        Instantiate (BaseBall, BallLocation.position, BallLocation.rotation);
    }
}

How to spawn prefabs within a certain period of time in Unity?

4 Answers4

Use Coroutines