Add a component 1 time in LateUpdate

Questions & Answers
1

I have the GrayScale Image Effect, that put all the screen white and black, so i have too in my
LateUpdate void that when my Life is lower that 16 I add the GrayScale effect to the MainCamera, but this GrayScale
is added infinitely how i can add it 1 time?
this is my Script:

        void LateUpdate()
        {
            LowLife();
        }

 void LowLife()
        {
            Grayscale grayscale;

            if (currentHealth <= lowLife)
            {
                Camera.main.gameObject.AddComponent<Grayscale>(); // Add the GrayScale

                if (!lowLifeSource.isPlaying && !dead)
                {
                    lowLifeSource.clip = heartClip;
                    lowLifeSource.Play();
                }
            }
            else
            {
                if (!dead)
                {
                    
                    lowLifeSource.Stop();
                }
            }
        }
2

try this:

    if(Camera.main.gameObject.GetComponent<Grayscale>()==null)
    {
       Camera.main.gameObject.AddComponent<Grayscale>();
    }
3

if(Camera.main.gameObject.GetComponent()==null)

Camera.main.gameObject.AddComponent();

4

Running GetComponent() method during every frame is a terrible idea. Instead, introduce a bool field to your script which changes its state depending on if GrayScale is added or not. The code will look something like this.

private bool _isGrayScaleAdded;

void LateUpdate()
{
	LowLife();
}
void LowLife()
{
	 Grayscale grayscale;

	 if (currentHealth <= lowLife)
	 {
	 
		//This part checks if you've already added it or not.
		if(!_isGrayScaleAdded){
			if(Camera.main.gameObject.GetComponent<GrayScale> == null)
				Camera.main.gameObject.AddComponent<Grayscale>(); // Add the GrayScale
			_isGrayScaleAdded = true; //Changing this value to true makes sure it won't be added again and also makes sure GetComponent method won't be called again
		}
		 

		 if (!lowLifeSource.isPlaying && !dead)
		 {
			 lowLifeSource.clip = heartClip;
			 lowLifeSource.Play();
		 }
	 }
	 else
	 {
		 if (!dead)
		 {
			 
			 lowLifeSource.Stop();
		 }
	 }
}