Replace Input.GetKey(KeyCode.Mouse0) with New Input System

Question

I was implementing the new Input system for my game, when I saw that I still had a script in my player that wouldnt allow me to start the scene, because the script still operated with the old input manager. Its probably just because I literally ask him to do so, in line 24, I think. I was still wondering if someone could tell me, how to actually use the new input system for this script and how I would have to change the script for it. And also btw I actually want to use it with an xbox one controller, if that would change anthing. Heres the script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.InputSystem;

public class PlayerAttack : MonoBehaviour{

private float timeBtwAttack;
public float startTimeBtwAttack;
PlayerControls controls;
public Transform attackPos;
public LayerMask whatIsEnemies;
//public Animator camAnim;
//public Animator playerAnim;
public float attackRangeX;
public float attackRangeY;
public int damage;

void Update(){
    
    if(timeBtwAttack <= 0){

        if(Input.GetKey(KeyCode.Mouse0)){
            //camAnim.SetTrigger("shake");
            //playerAnim.SetTrigger("attack");
            Collider2D[] enemiesToDamage = Physics2D.OverlapBoxAll(attackPos.position, new       Vector2(attackRangeX, attackRangeY), 0, whatIsEnemies);
            for (int i = 0; i < enemiesToDamage.Length; i++) {
                enemiesToDamage[i].GetComponent<Enemy>().TakeDamage(damage);
            }
            timeBtwAttack = startTimeBtwAttack;
        }
    
} else  {          
    timeBtwAttack -= Time.deltaTime;   
 }

}void OnDrawGizmosSelected(){
        
        Gizmos.color = Color.black;
        Gizmos.DrawWireCube(attackPos.position, new Vector3(attackRangeX, attackRangeY, 1));

  }
}

Answer 1

If you want a quick&dirty drop-in replacement:

if( Mouse.current.leftButton.wasPressedThisFrame ) {

However, that's not how the new input system is supposed to be used. The old input system was based on the philosophy that you poll the state of the input devices during Update. The new input system is based on events. You don't ask the system what's the input state; the system tells you that an input event occurred by calling a callback method. But doing it like that requires that you completely rethink the way you handle input in your game.

What you usually have in a project using the new input system is:

1. An Input Actions asset which allows you to define semantic input actions (like "shoot") and then assign multiple controls to them (like left mouse button, Gamepad button X, keyboard keys Space and x and pressing the touchscreen).
2. A bunch of handler-methods on various scripts which are supposed to be called when one of those semantic input actions happens
3. A PlayerInput component which links semantic actions to the handler-methods.

But explaining the whole thing from start to finish would be yet another Unity new input system tutorial. Others have already created enough of those which are easy to find with your preferred search engine. Or you could read the manual which also offers a pretty good introduction into how to use the system efficiently.