c# - Issue with my script; An object reference is required to access non-static member

I'm having an issue with my script and I don't have a clue what is wrong.

The error I get is:

Assets/Scripts/BlackBirdDrag.cs(43,41): An object reference is required to access non-static member `UnityEngine.Rigidbody2D.isKinematic'

Here is the script:

using UnityEngine;
using System.Collections;

public class BlackBirdDrag : MonoBehaviour {


  public float maxStreatch = 3.0f;
  public LineRenderer catapultLineFront;
  public LineRenderer catapultLineBack;

  private SpringJoint2D spring;
  private Transform catapult;
  private Ray rayToMouse;
  private Ray leftCatapultToProjectile;
  private float maxStretchSqr;

  private bool clickedOn;
  private float circlRadius;
  private Vector2 prevVelocity;
  //private GameObject circle;



  void Awake () {
    spring = GetComponent  ();
    catapult = spring.connectedBody.transform;

  }

  void Start () {

    LineRendererSetup ();
    rayToMouse = new Ray(catapult.position, Vector3.zero);
    leftCatapultToProjectile = new Ray(catapultLineFront.transform.position, Vector3.zero);
    maxStretchSqr = maxStreatch * maxStreatch;
    CircleCollider2D circle = Collider2D as CircleCollider2D;
    circlRadius = circle.radius;

  }


  void Update () {
    if(clickedOn)
      Dragging ();

    if(spring != null) {
      if(!Rigidbody2D.isKinematic && prevVelocity.sqrMagnitude > Rigidbody2D.velocity.sqrMagnitude) {
        Destroy (spring);

        Rigidbody2D.velocity = prevVelocity;
      }
      if(!clickedOn)
        prevVelocity = Rigidbody2D.velocity;

      LineRendererupdate ();

    }else{
      catapultLineFront.enabled = false;
      catapultLineBack.enabled = false;

    }

  }

  void LineRendererSetup () {
    catapultLineBack.SetPosition(0,catapultLineBack.transform.position);
    catapultLineFront.SetPosition(0,catapultLineFront.transform.position);

    catapultLineBack.sortingLayerName = "foreground";
    catapultLineFront.sortingLayerName = "foreground";


    catapultLineBack.sortingOrder = 1;
    catapultLineFront.sortingOrder = 3;

  }

  void OnMouseDown () {
    spring.enabled = false;
    clickedOn = true;
  }


  void OnMouseUp () {
    spring.enabled = true;
    Rigidbody2D.isKinematic = false;
    clickedOn = false;
  }

  void LineRendererupdate () {
    Vector2 catapultToProjectile = transform.position - catapultLineFront.transform.position;
    leftCatapultToProjectile.direction = catapultToProjectile;

    Vector3 holdpoint = leftCatapultToProjectile.GetPoint(catapultToProjectile.magnitude + circlRadius);
    catapultLineBack.SetPosition(1, holdpoint);
    catapultLineFront.SetPosition(1, holdpoint);
  }

  void Dragging () {
    Vector3 mouseWorldPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);
    Vector2 catapultToMouse = mouseWorldPoint - catapult.position;

    if(catapultToMouse.sqrMagnitude > maxStretchSqr) {

      rayToMouse.direction = catapultToMouse;
      mouseWorldPoint = rayToMouse.GetPoint(maxStreatch);
    }

    mouseWorldPoint.z = 0f;
    transform.position = mouseWorldPoint;
  }

}

Answer

I'm not familiar with Unity.

Your issue is that you try to call methods on a Class instead of calling methods on an instance of a Class, i.e. on an Object.

Specifically, the issue shows up in two places:

First, in Update()

if(spring != null) {
  if(!Rigidbody2D.isKinematic ...

and later, in OnMouseUp()

  void OnMouseUp () {
    spring.enabled = true;

    Rigidbody2D.isKinematic = false;
    clickedOn = false;
  }

RigidBody2D doesn't have a static member called isKinematic. Only instances of it have such a member.

You must fetch the instance of the Rigidbody2D component and call the methods on that instead.

Here is an example (retrieved from here).

using UnityEngine;
using System.Collections;


public class ExampleClass : MonoBehaviour {
    public Rigidbody rb;
    void Start() {
        rb = GetComponent();
    }
    void FixedUpdate() {
        rb.AddForce(Vector3.up);
    }
}

Then you'll be able to call the functions on the variable rb if you follow the example. ie. rb.isKinematic