Why is Input.GetAxisRaw("Horizontal") return 8.725659e-15 when it should be 0

[Sakuyurixxx]

new to unity, at first i use Input.GetAxisRaw(“Horizontal”) in one ‘playercontroller’ script to control player’s movement, and everything worked fine, player’s velocity.x only got -1/0/1. But when i use it in a state machine, i got this problem:

when i press a/d , player’s velocity.x set to -1/1 and it’s fine, then i release the button, velocity.x should return to 0 immediately but it first return to some strange number like 8.725659e-15, then to 0

刚学unity，我一开始只用playercontroller一个脚本控制角色所有行动，在这个脚本里用 Input.GetAxisRaw(“Horizontal”)控制玩家左右移动，然后也没什么问题，后来接触到状态机，在对着教程写代码的时候出现了这个问题：

按a/d进行移动时，velocity.x正常被设定为-1/1，但是松开按键后rigidbody里的velocity.x不会立即回到0，而是先回到一个类似8.725659e-15这样莫名其妙的值，然后再回到0。

Player.cs

public class Player : MonoBehaviour
{
    [Header("Move Info")]
    public float moveSpeed;
    #region 定义Unity组件
    public Animator anim { get; private set; }
    public Rigidbody2D rb { get; private set; }
    #endregion
    #region 定义States
    public PlayerStateMachine stateMachine { get; private set; }
    public PlayerIdleState idleState { get; private set; }
    public PlayerMoveState moveState { get; private set; }

    #endregion
    private void Awake()
    {
        stateMachine = new PlayerStateMachine();
        idleState = new PlayerIdleState(this, stateMachine, "Idle");
        moveState = new PlayerMoveState(this, stateMachine, "Move");

    }
    private void Start()
    {
        anim = GetComponentInChildren<Animator>();
        rb = GetComponent<Rigidbody2D>();
        stateMachine.Initialize(idleState);
    }
    private void Update()
    {
        stateMachine.currentState.Update();
    }

    public void SetVelocity(float _xVelocity, float _yVelocity)
    {
        rb.velocity = new Vector2(_xVelocity, _yVelocity);
    }
}

PlayerState.cs

//被继承的总类，后面的所以state都需要继承它
//实际上Player并没有进入过这个状态，没有调用此脚本，所有的调用均属于此脚本的子脚本
public class PlayerState
{
    protected PlayerStateMachine stateMachine;//创建PlayerStateMachine类，以承接来自Player.cs传过来的东西
    protected Player player;//创建Player类，以承接来自Player.cs传过来的东西

    #region Unity组件
    protected Rigidbody2D rb;//纯简化，将player.rb --> rb
    #endregion

    private string animBoolName;
    protected float xInput;
    public PlayerState(Player _player, PlayerStateMachine _stateMachine, string _animBoolName)
    {
        this.player = _player;
        this.stateMachine = _stateMachine;
        this.animBoolName = _animBoolName;
    }//构造函数，用于传递信息

    public virtual void Enter()
    {
        player.anim.SetBool(animBoolName, true);//通过animator自带的函数，将animator里的Bool值改变为想要的值
        rb = player.rb;//纯简化，将player.rb --> rb
    }
    public virtual void Update()
    {

        xInput = Input.GetAxisRaw("Horizontal");//对于键盘和游戏杆输入，该值将处于 -1...1 的范围内。 由于未对输入进行平滑处理，键盘输入将始终为 -1、0 或 1。 如果您想自己完成键盘输入的所有平滑处理，这非常有用。
    }
    public virtual void Exit()
    {
        player.anim.SetBool(animBoolName, false);
    }

}

PlayeyMoveState.cs

public class PlayerMoveState : PlayerState
{
    public PlayerMoveState(Player _player, PlayerStateMachine _playerStateMachine, string _animBoolName) : base(_player, _playerStateMachine, _animBoolName)
    {
    }

    public override void Enter()
    {
        base.Enter();
    }

    public override void Exit()
    {
        base.Exit();
    }

    public override void Update()
    {
        base.Update();

        player.SetVelocity(xInput, player.rb.velocity.y);


        if (xInput == 0)
            stateMachine.ChangeState(player.idleState);
    }
}

PlayerStateMachine.cs

public class PlayerStateMachine
{
    /// <summary>
    /// 用来切换状态
    /// </summary>
    public PlayerState currentState { get; private set; }

    public void Initialize(PlayerState _startState)
    {
        currentState = _startState;
        currentState.Enter();

    }

    public void ChangeState(PlayerState _newState)
    {
        currentState.Exit();
        currentState = _newState;
        currentState.Enter();
    }
}

PlayerIdleState.cs

public class PlayerIdleState : PlayerState
{
    public PlayerIdleState(Player _player, PlayerStateMachine _playerStateMachine, string _animBoolName) : base(_player, _playerStateMachine, _animBoolName)
    {
    }

    public override void Enter()
    {
        base.Enter();
    }

    public override void Exit()
    {
        base.Exit();
    }

    public override void Update()
    {
        base.Update();


        if (xInput != 0)
            stateMachine.ChangeState(player.moveState);
    }
}

[ArachnidAnimal]

The number (8.725659e-15) is in scientific format. It means 8.7 x 10^-15.
This is essentially 0.

If you need to check if the number is 0, you should use:

if (Mathf.Approximately(xInput, 0f)) instead of using the == or != operators.