Input.GetAxis("Horizontal") ，一直输出为 0

using System.Collections;

using System.Collections.Generic;

using UnityEngine;

public class main : MonoBehaviour {

    // Use this for initialization

    void Start () {

        Debug.Log("y  " + Input.GetAxis("Horizontal"));

//输出 y 0

    }

// Update is called once per frame

void Update () {

}

}