How to access a variable from another class (GetComponent()?)

Questions & Answers
1

Hi.

    I am new to Unity and my programming skills are very rusty. Please help me with my Unity3D problem.

I have 2 classes.
public class Ball: MonoBehaviour
()
public class Star: MonoBehaviour
()

Ball playerBall; //is the main player game object in the Unity Hierarchy
Star itemStar; //is a star item game object in the Unity Hierarchy // the playerBall collects stars within the game world.

My question is how can I access a variable from another class.

int starCount;// is a variable inside of the Ball script

I want to access the variable starCount from inside the Star script.

//The following OnTriggerEnter(Collider collision) is located inside the Star script
void OnTriggerEnter(Collider collision)
{
if (collision.gameObject.tag == "ballTriggerCollision")
{
Ball tempBall;
tempBall= this.GetComponent("Ball") as Ball;
tempBall.GetComponent<Ball>().starCount += 1; // ****** THIS IS THE LINE THAT CREATES THE ERROR

killStar();

}
}

The game runs fine until the exact same moment that the Ball Trigger collider collides with the star.
I get an error.

NullReferenceException: Object reference not set to an instance of an object
Ball.OnTriggerEnter (UnityEngine.Collider collision) (at Assets/Scripts/Ball.cs:97)
UnityEditor.Toolbar:OnGUI()

tempBall.GetComponent<Ball>().starCount += 1; // ****** THIS IS THE LINE THAT CREATES THE ERROR

I don't want to add the Ball game object as a variable on the Star script because then I will need to rewrite much of my game code.

If you can help me then I thank you for your help in advance. Your time and energy is appreciated.
2

The error comes from that line :

tempBall= this.GetComponent("Ball") as Ball;

As you can see, you’re getting the component from “this”, which is the star. What you want instead, is to get the component from the ball’s gameObject. So, do this instead :

tempBall = collision.gameObject.GetComponent<Ball>();
tempBall.starCount += 1; // You could test if tempBall is != null, unless you're sure it won't be.