Swapping item in the inventory

Hey There! I have been making a UI inventory like click first item and second item to swap their position along slots. But the line in the commented below called problem starts - ends, items cliked are not swapped.Always the first clicked one change its properties as second one but the second always the same.

 //Itemdata script includes eventSystems events like 
 //OnPointerClick to execute MoveItem method by 
 //clicking to the slot.
  

 ItemData firstSlot, secondSlot;
 
 
 
 public void MoveItem(GameObject clicked)
     {
         if (firstSlot== null)
         {
              //the -1 means if there is an item in the slot
             if (clicked.GetComponent<ItemData>().item.id != -1)
             {
                 Debug.Log("clicked first slot");
                 firstSlot = clicked.GetComponent<ItemData>();
                 firstSlot.GetComponent<Image>().color = Color.gray;
             }
 
         }
 
         else if (secondSlot == null)
         {
             Debug.Log("clicked second slot");
             secondSlot= clicked.GetComponent<ItemData>();
         }
 
         if (secondSlot != null && firstSlot != null)
         {
             Debug.Log("firstSlot AND secondSlot ARE NOT NULL ANYMORE");
        //Problem lines starts

             firstSlot.GetComponent<Image>().sprite = secondSlot.GetComponent<Image>().sprite;

             secondSlot.GetComponent<Image>.sprite = firstSlot.GetComponent<Image>().sprite;
             
         //Problem lines ends

             secondSlot.GetComponent<ItemData>().item = firstSlot.GetComponent<ItemData>().item;

             firstSlot.GetComponent<Image>().color = Color.white;
             firstSlot= null;
             secondSlot = null;
         }
 
 
     }