gather-and-defend/Assets/Scripts/Drag&Drop/UnitPlacementButton.cs

using System.Collections;
using System.Collections.Generic;
using TMPro;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
using GatherAndDefend.Events;

[RequireComponent(typeof(Button))]
public abstract class UnitPlacementButton : MonoBehaviour, IPointerDownHandler
{
    [SerializeField]
    protected Material _outlineMaterial;
    [SerializeField]
    protected Sprite _detectionRangeSprite;

    [SerializeField]
    protected int _wood;
    [SerializeField]
    protected int _rock;
    [SerializeField]
    protected int _food;

    protected Button _button;
    [SerializeField]
    private TMP_Text _foodLabel;
    [SerializeField]
    private TMP_Text _woodLabel;
    [SerializeField]
    private TMP_Text _rockLabel;

    protected bool _canSpawn = false;

    protected virtual void Start()
    {
        _button = GetComponent<Button>();

        _button.enabled = false;
        EventAggregator.Instance.GetEvent<LevelLoadedEvent>().Attach(OnLevelLoaded);
        EventAggregator.Instance.GetEvent<ExitingLevelEvent>().Attach(DeactivateButton);
    }
    private void OnLevelLoaded(GatherAndDefend.LevelEditor.Level level)
    {
        _canSpawn = true;
        EventAggregator.Instance.GetEvent<LevelLoadedEvent>().Detach(OnLevelLoaded);
    }

    void DeactivateButton() 
    {
        EventAggregator.Instance.GetEvent<ExitingLevelEvent>().Detach(DeactivateButton);
        _canSpawn = false;
    }
    protected virtual void Update()
    {
        _button.interactable = CanPlace();

        SetTextFor(_foodLabel, _food);
        SetTextFor(_rockLabel, _rock);
        SetTextFor(_woodLabel, _wood);
    }
    void SetTextFor(TMP_Text label, int value)
    {
        label.transform.parent.gameObject.SetActive(value > 0);
        label.text = "" + value;
    }
    public void OnPointerDown(PointerEventData eventData)
    {
        if (!_button.interactable) return;

        var placeholder = Place();
        placeholder.Rock = _rock;
        placeholder.Wood = _wood;
        placeholder.Food = _food;
    }
    protected abstract DraggablePlaceholder Place();
    protected abstract bool CanPlace();
}