call method from another script C# Unity3d

Question

I want to call another script method (stars) when object is destroyed, Below is my code so far I had done, I am getting error (Null reference) at line "tim.stars", Any suggestions what I had done wrong? Here is my code.

using UnityEngine;
using System.Collections;
public class clear : MonoBehaviour {
// Use this for initialization
void Start () {
    GetComponent<ParticleSystem> ().emissionRate = 0;
}
// Update is called once per frame
void Update () {
    if (Input.GetMouseButtonDown (1)) {
        GetComponent<ParticleSystem> ().Emit (10);
    }
}
void OnParticleCollision(GameObject obj)
{
    if (obj.gameObject.tag == "fire1") {
        Destroy (obj, 5.0f);
        TimingForIndust2 tim = GetComponent<TimingForIndust2> ();
        tim.stars ();
    }
        StartCoroutine (TestCoroutine());
    }
IEnumerator TestCoroutine(){
    yield return new WaitForSeconds(8);
    Application.LoadLevel (25);
}
}

here is my 2nd script TimingForIndust2

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using MadLevelManager;
public class TimingForIndust2 : MonoBehaviour {
public Transform TimingBar;
public Transform TextIndicator;
public Transform TextRemaining;
[SerializeField] private float currentAmount;
[SerializeField] private float speed;

// method to reduce the time continously
void Update () {

    if (currentAmount > 0) {
        currentAmount -= speed*Time.deltaTime;
        TextIndicator.GetComponent<Text>().text=((int)currentAmount).ToString()+"s";
        TextRemaining.gameObject.SetActive(true);

    } else {
        TextRemaining.gameObject.SetActive(false);
        TextIndicator.GetComponent<Text>().text="TimeUP";
        Application.LoadLevel (62);

    }
    TimingBar.GetComponent<Image> ().fillAmount = currentAmount / 60;
}
public void stars()
{
    if (currentAmount > 45.0f) {

        MadLevelProfile.SetLevelBoolean (MadLevel.currentLevelName, "star_1", true);
        MadLevelProfile.SetLevelBoolean (MadLevel.currentLevelName, "star_2", true);
        MadLevelProfile.SetCompleted (MadLevel.currentLevelName, true);
    } else if (currentAmount > 20.0f && currentAmount < 29.0f) {

        MadLevelProfile.SetLevelBoolean (MadLevel.currentLevelName, "star_1", true);
        MadLevelProfile.SetLevelBoolean (MadLevel.currentLevelName, "star_2", true);
        MadLevelProfile.SetCompleted (MadLevel.currentLevelName, true);

    } else if (currentAmount > 2.0f && currentAmount < 19.0f) {

        MadLevelProfile.SetLevelBoolean (MadLevel.currentLevelName, "star_1", true);
    }
}
}

Answer 1

By reading your comment, you have to Find the Timer with GameObject.Find then get the component from it. You can't be doing this each time there is a collision. You have to cache it in the Start() function once then re-use it.

I also cached ParticleSystem in the new code. Also, instead of comparing tag directly with obj.gameObject.tag == "fire1" , use the CompareTag function to compare tags.

This should fix your problem. Now, it's your job to cache the Text component that is attached to the TextIndicator script which you are calling in the updat function from the TimingForIndust2 script.

using UnityEngine;
using System.Collections;
public class clear : MonoBehaviour {
TimingForIndust2 timingForIndust2;

ParticleSystem particles;

// Use this for initialization
void Start () {
    particles = GetComponent<ParticleSystem> ();
    particles.emissionRate = 0;

    GameObject tempObj = GameObject.Find("Timer");
    timingForIndust2 = tempObj.GetComponent<TimingForIndust2>();
}
// Update is called once per frame
void Update () {
    if (Input.GetMouseButtonDown (1)) {
        particles.Emit (10);
    }
}
void OnParticleCollision(GameObject obj)
{
    if (obj.CompareTag("fire1")) {
        Destroy (obj, 5.0f);
        timingForIndust2.stars ();
    }
        StartCoroutine (TestCoroutine());
    }
IEnumerator TestCoroutine(){
    yield return new WaitForSeconds(8);
    Application.LoadLevel (25);
}
}