you can now sell Items with Right Mouse Click on an InventorySlot for the Item.SellPrice

and it gets put into the Shop for full price

renamed Item.cost to Item.price

Assets/Scenes/MainScene.unity

@@ -6456,7 +6456,7 @@ MonoBehaviour:
   m_EditorClassIdentifier: 
   itemsParent: {fileID: 610140154}
   shopUI: {fileID: 1671356616}
-  inventoryUI: {fileID: 971652020}
+  inventoryUI: {fileID: 1609015285}
 --- !u!224 &1551890462 stripped
 RectTransform:
   m_CorrespondingSourceObject: {fileID: 3510585822996971025, guid: 44dae5fbdb6f7df4f93a10807f66956f, type: 3}
@@ -6651,7 +6651,9 @@ MonoBehaviour:
   - {fileID: 11400000, guid: bb9777a7d5804bd6bf25d5510206aaf0, type: 2}
   - {fileID: 11400000, guid: bb9777a7d5804bd6bf25d5510206aaf0, type: 2}
   - {fileID: 11400000, guid: 008a8fdd2c3a95745acafee4087a855d, type: 2}
-  itemWasSold: 0
+  - {fileID: 11400000, guid: d651d57ba97a4246a0094409e29fe56a, type: 2}
+  - {fileID: 11400000, guid: d651d57ba97a4246a0094409e29fe56a, type: 2}
+  itemWasBought: 0
 --- !u!1001 &1701153146
 PrefabInstance:
   m_ObjectHideFlags: 0

Assets/Scripts/InventorySlot.cs

@@ -1,6 +1,18 @@
+using System;
 using UnityEngine;
+using UnityEngine.EventSystems;
+
+public class InventorySlot : ItemStorageSlot, IPointerClickHandler {
+    private Inventory _inventory;
+    private Shop _shop;
+    private PlayerController _playerController;
+
+    private void Start() {
+        _inventory = Inventory.instance;
+        _shop = Shop.instance;
+        _playerController = PlayerController.instance;
+    }
 
-public class InventorySlot : ItemStorageSlot {
     /**
      * Gets called when the Inventory Slot is clicked
      */
@@ -14,4 +26,25 @@ public class InventorySlot : ItemStorageSlot {
             }
         }
     }
+
+    /**
+     * Sells the Item for the Item Sell Price and puts it in the Shop if the selling was a mistake
+     */
+    private void SellItem() {
+        if(Item){
+            _playerController.ChangeMoney(Item.SellPrice);
+            _shop.AddItem(Item, 1);
+            _inventory.RemoveItem(Item, 1); // TODO: somehow sell more than 1 Item
+        }
+    }
+
+    /**
+     * Gets called when the Inventory Slot gets clicked on
+     */
+    public void OnPointerClick(PointerEventData eventData) {
+        // When clicked on with right Mouse Button sell the Item
+        if(eventData.button == PointerEventData.InputButton.Right) {
+            SellItem();
+        }
+    }
 }

Assets/Scripts/Item.cs

@@ -8,8 +8,8 @@ public class Item : ScriptableObject, IComparable<Item> {
     public int id;  //TODO: create an actual ID System that makes snens
     public Sprite selectedSprite;
     public Sprite defaultSprite;
-    public int cost;
-    public int SellPrice => Convert.ToInt32(cost * 0.8);
+    public int price;
+    public int SellPrice => Convert.ToInt32(price * 0.8);
     
     public Item(string displayName, string description, int id) {
         this.displayName = displayName;

Assets/Scripts/PlayerController.cs

@@ -25,7 +25,7 @@ public class PlayerController : MonoBehaviour {
     private int _money;
     private UsableItem _selectedItem;
 
-    public int startMoney = 100;
+    public int startMoney;
     public TextMeshProUGUI moneyTextMeshProUGUI;
 
     public int Money => _money;
@@ -35,8 +35,9 @@ public class PlayerController : MonoBehaviour {
     
     // Start is called before the first frame update
     private void Start() {
-        _money = startMoney;
         _inventory = Inventory.instance;
+        _money = startMoney;
+        UpdateMoneyUI();
 
         onMoneyChangedCallback += UpdateMoneyUI;
     }
@@ -56,6 +57,7 @@ public class PlayerController : MonoBehaviour {
 
     public void ChangeMoney(int amount) {
         _money += amount;
+        
         onMoneyChangedCallback?.Invoke();
     }
 

Assets/Scripts/Shop.cs

@@ -39,7 +39,7 @@ public class Shop : ItemStorage {
             _playerController = PlayerController.instance;
 
             if(_lastBoughtItem) {
-                _playerController.ChangeMoney(_lastBoughtItem.cost);
+                _playerController.ChangeMoney(_lastBoughtItem.price);
                 _inventory.RemoveItem(_lastBoughtItem, _lastBoughtItemAmount);
                 AddItem(_lastBoughtItem, _lastBoughtItemAmount);
                 itemWasBought = false;

Assets/Scripts/ShopSlot.cs

@@ -31,9 +31,9 @@ public class ShopSlot : ItemStorageSlot {
      */
     public override void UseItem() {
         if(Item) {
-            if(_playerController.Money >= Item.cost) {
+            if(_playerController.Money >= Item.price) {
                 if(Item) {
-                    _playerController.ChangeMoney(-Item.cost);
+                    _playerController.ChangeMoney(-Item.price);
                     _shop.itemWasBought = true;
                     
                     Debug.Log("Buying Item: " + Item.displayName);

Assets/Scripts/ShopUI.cs

@@ -35,7 +35,7 @@ public class ShopUI : MonoBehaviour {
      * Turn on/off the Shop UI
      */
     private void ToggleShop() {
-        // TODO: geht ned oda so: inventoryUI.gameObject.SetActive(!shopUI.activeSelf);
+        inventoryUI.gameObject.SetActive(!shopUI.activeSelf);
         shopUI.SetActive(!shopUI.activeSelf);
     }
 
@@ -48,7 +48,7 @@ public class ShopUI : MonoBehaviour {
             if (i < _shop.items.Count) {
                 _slots[i].AddItem(_shop.items.ElementAt(i).Key);
                 _slots[i].nameText.text = _slots[i].Item.displayName;
-                _slots[i].costText.text = _slots[i].Item.cost + " µ";
+                _slots[i].costText.text = _slots[i].Item.price + " µ";
                 _slots[i].amountText.text = _shop.items[_shop.items.ElementAt(i).Key] + " #";
             }
             else {