官方教材：
https://unity3d.com/cn/learn/tutorials/topics/navigation/creating-click-move-game?playlist=17105

using UnityEngine;
using System.Collections;

namespace CompleteProject
{

    public class ClickToMove : MonoBehaviour {

        public float shootDistance = 10f;
        public float shootRate = .5f;
        public PlayerShooting shootingScript;

        private Animator anim;
        private NavMeshAgent navMeshAgent;
        private Transform targetedEnemy;
        private Ray shootRay;
        private RaycastHit shootHit;
        private bool walking;
        private bool enemyClicked;
        private float nextFire;

        // Use this for initialization
        void Awake () 
        {
            anim = GetComponent<Animator> ();
            navMeshAgent = GetComponent<NavMeshAgent> ();
        }
        
        // Update is called once per frame
        void Update () 
        {
            Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
            RaycastHit hit;
            if (Input.GetButtonDown ("Fire2")) 
            {
                if (Physics.Raycast(ray, out hit, 100))
                {
                    if (hit.collider.CompareTag("Enemy"))
                    {
                        targetedEnemy = hit.transform;
                        enemyClicked = true;
                    }

                    else
                    {
                        walking = true;
                        enemyClicked = false;
                        navMeshAgent.destination = hit.point;
                        navMeshAgent.Resume();
                    }
                }
            }

            if (enemyClicked) {
                MoveAndShoot();
            }

            if (navMeshAgent.remainingDistance <= navMeshAgent.stoppingDistance) {
                if (!navMeshAgent.hasPath || Mathf.Abs (navMeshAgent.velocity.sqrMagnitude) < float.Epsilon)
                walking = false;
            } else {
                walking = true;
            }

            anim.SetBool ("IsWalking", walking);
        }

        private void MoveAndShoot()
        {
            if (targetedEnemy == null)
                return;
            navMeshAgent.destination = targetedEnemy.position;
            if (navMeshAgent.remainingDistance >= shootDistance) {
            
                navMeshAgent.Resume();
                walking = true;
            }

            if (navMeshAgent.remainingDistance <= shootDistance) {
            
                transform.LookAt(targetedEnemy);
                Vector3 dirToShoot = targetedEnemy.transform.position - transform.position;
                if (Time.time > nextFire)
                {
                    nextFire = Time.time + shootRate;
                    shootingScript.Shoot(dirToShoot);
                }
                navMeshAgent.Stop();
                walking = false;
            }
        }
    }
}