CODEWITHSUNDEEP
c#unity-game-engineunity3d-2dtools
KGSB
KGSB

Reputation: 39

Moving a Physics Sprite in Unity

How do I move a physics sprite in Unity? Do I apply force to the body like in farseers physics, or do I move the character sprite? This is how I'm currently trying to move it and im getting:

NullReferenceException: UnityEngine.Rigidbody2D.get_velocity()

    _position.x = Input.GetAxis ("Horizontal");
    _position.y = Input.GetAxis ("Vertical");

    if (Input.GetKeyDown(KeyCode.Space))
    {   
        _rig.AddForce(new Vector2(_rig.velocity.x, _jumpHeight));
        _rig.velocity = new Vector2(Mathf.Clamp(_rig.velocity.x, -_clampValue.x, _clampValue.x), Mathf.Clamp(_rig.velocity.y, -_clampValue.y, _clampValue.y));
    }

    if (Input.GetKey(KeyCode.D))
    {
        //_rig.AddForce(new Vector2(_moveSpeed, _rig.velocity.x));
        //_rig.velocity = new Vector2(Mathf.Clamp(_rig.velocity.x, -_clampValue.x, _clampValue.x), Mathf.Clamp(_rig.velocity.y, -_clampValue.y, _clampValue.y));
        _rig.velocity = new Vector2(_position.x * _moveSpeed, _rig.velocity.y);
    }

    if (Input.GetKey(KeyCode.A))
    {
        _rig.AddForce(new Vector2(-_moveSpeed, _rig.velocity.y));
        _rig.velocity = new Vector2(Mathf.Clamp(_rig.velocity.x, -_clampValue.x, _clampValue.x), Mathf.Clamp(_rig.velocity.y, -_clampValue.y, _clampValue.y));
    }

Upvotes: 0

Views: 678

Answers (1)

ReMinoer
ReMinoer

Reputation: 402

It simply seems that you didn't assign RigidBody2D to your sprite.

I suppose that _rig is assigned this way in your Start or Awake method :

_rig = GetComponent<Rigidbody2D>();

But if you don't have assign a Rigidbody2D to your GameObject, it will return a null reference. That is the reason of the exception.

Go in the Editor, select your GameObject in Hierarchy panel, then add a component Rigidbody2D to it in the Inspector panel.

The way you add forces is also false. You need to pass a Vector2 that represent the direction of the move. By the way, you can't clamp a velocity in negative value because velocity is always positive.

To conclude, you made a mistake in the way you handled the inputs. You use Input.GetAxis to get the axis value and the A and D keys to launch the move. Maybe it can work because A and D are the keys use for Horizontal and Vertical axis by default but it can cause errors later.

For all these reasons, I suggest that you to edit your code this way :

float horizontal = Input.GetAxis ("Horizontal");

if (Input.GetKeyDown(KeyCode.Space))
    _rig.AddForce(new Vector2(0, _jumpHeight));

if (horizontal < 0)
    _rig.AddForce(new Vector2(-_moveSpeed, 0));
if (horizontal > 0)
    _rig.AddForce(new Vector2(_moveSpeed, 0));

if (_rig.velocity.x > _clampValue.x)
    _rig.velocity = new Vector2(_clampValue.x, _rig.velocity.y);
if (_rig.velocity.y > _clampValue.y)
    _rig.velocity = new Vector2(_rig.velocity.x, _clampValue.y);

Upvotes: 2

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