如何防止玩家在 Unity3d 中穿过墙壁

我有以下播放器控制器：

using UnityEngine;
using UnityEngine.Networking;
using System.Collections;
[RequireComponent(typeof(NetworkIdentity))]
public class PlayerController : NetworkBehaviour {
    public Vector3 size = new Vector3(1, 1, 1);
    public float speed = 10;
    public float rotateSpeed = 9;
    private Transform _transform;
    private Map _map;
    private BoxCollider _collider;
    private bool _active = false;
    private Vector3 _lastPosition;
    private bool _isGrounded = false;
    void Start () {
        _transform = transform;
        Messenger.AddListener ("MAP_LOADED", OnMapLoaded);
        _transform.localPosition = new Vector3 (-100, -100, -100);
        gameObject.name = "Player " + gameObject.GetComponent<NetworkIdentity> ().netId.Value;
        _collider = gameObject.GetComponent<BoxCollider> ();
        _map = GameObject.Find ("Map").GetComponent<Map> ();
        _collider.size = size;
    }
    void OnMapLoaded () {
        if (isLocalPlayer) {
            // Hook up the camera
            PlayerCamera cam = Camera.main.GetComponent<PlayerCamera>();
            cam.target = transform;
            // Move the player to the it's spawn location
            _transform.localPosition = _map.GetPlayerSpawn();
        }
        // Set the player as active
        _active = true;
    }
    void Update () {
        if (!isLocalPlayer || !_active) {
            return;
        }
        _lastPosition = _transform.position;
        float transAmount = speed * Time.deltaTime;
        float rotateAmount = rotateSpeed * Time.deltaTime;
        if (Input.GetKey ("up")) {
            transform.Translate (0, 0, transAmount);
        }
        if (Input.GetKey ("down")) {
            transform.Translate (0, 0, -transAmount);
        }
        if (Input.GetKey ("left")) {
            transform.Rotate (0, -rotateAmount, 0);
        }
        if (Input.GetKey ("right")) {
            transform.Rotate (0, rotateAmount, 0);
        }
        if (!_isGrounded) {
            Vector3 down = _transform.TransformDirection(Vector3.down);
            _transform.position += down * Time.deltaTime * _map.gravity;
        }
    }
    void FixedUpdate () {
        //
        // Check what is below us
        //
        Vector3 down = _transform.TransformDirection(Vector3.down);
        RaycastHit[] hits;
        hits = Physics.RaycastAll(_transform.position, down, size.y + 0.001f);
        _isGrounded = false;
        foreach (RaycastHit hit in hits) {
            if (hit.collider.gameObject.tag.ToUpper() == "GROUND") {
                _isGrounded = true;
            }
        }
    }
    void OnTriggerEnter(Collider collider) {
        Debug.Log ("Triggered by " + collider.gameObject.tag.ToUpper ());
        if (collider.gameObject.tag.ToUpper () == "GROUND") {
            transform.position = _lastPosition;
        }
    }
}

在Update中，我正在获取用户的输入并移动转换。在FixedUpdate中，我正在检查玩家是否在地面上并适当地设置标志。最后，在OnTriggerEnter，我正在检查我是否正在尝试经历任何事情。

如果我在OnTriggerEnter击中了什么，我会尝试将玩家的位置恢复到一个好的位置，但这并没有发生。我的猜测是因为_lastPosition不是我所期望的。

有没有更好的方法可以做到这一点？