Choose random prefabs from list?

Question

Hi, so i made a list with 10 prefabs in, and i want the shop to randomly pick 5 from the list everytime the shop is opened. I am really new to unity and have been following tutorials up to this point. Thanks. alt text

The code is

 namespace Assets.Scripts.UserInterface
 {
     public class StoreUIController : MonoBehaviour
     {
       
         public ItemList MerchantInventory;
 
         [SerializeField]
         private GameObject ItemTemplate;
         [SerializeField]
         private GameObject CurrencyTemplate;
         
         private Transform _scrollViewContent;
 
         private PlayerInventoryUIController _playerInventoryUI;
 
         private void Start()
         {
             _playerInventoryUI = FindObjectOfType<PlayerInventoryUIController>();
         }
 
         public void PopulateInventory(ItemList inventoryList)
         {
             ClearInventory();
             MerchantInventory = inventoryList;
 
             if (_scrollViewContent == null)
             {
                 _scrollViewContent = transform.Find("Scroll View").Find("Viewport").Find("Content"); ;
             }
 
             foreach (var item in inventoryList.ClothingItems)
             {
                 GameObject newItem = Instantiate(ItemTemplate, _scrollViewContent);
 
                 newItem.transform.localScale = Vector3.one;
                 newItem.transform.Find("Image").GetComponent<Image>().sprite = item.Sprite;
                 newItem.transform.Find("Name").GetComponent<Text>().text = item.Name;
                 newItem.transform.Find("Description").GetComponent<Text>().text = item.Description;
 
                 foreach (var cur in item.PurchasePrice)
                 {
                     GameObject newCurrency = Instantiate(CurrencyTemplate, newItem.transform.Find("Currency/List"));
 
                     newCurrency.transform.localScale = Vector3.one;
                     newCurrency.transform.Find("Image").GetComponent<Image>().sprite = cur.Currency.Image;
                     newCurrency.transform.Find("Amount").GetComponent<Text>().text = cur.Amount.ToString();
 
                 }
                 newItem.transform.Find("Currency").Find("BuyBtn").GetComponent<Button>().onClick.AddListener(BuyOnClick);
 
             }
             
 
         }
         public void ClearInventory()
         {
             MerchantInventory = null;
 
             //Since this starts out as disabled, we need to do a check the first time we try to access the content element, as we may not have a reference to it.
             if (_scrollViewContent == null)
             {
                 _scrollViewContent = transform.Find("Scroll View").Find("Viewport").Find("Content");
             }
 
             foreach (Transform child in _scrollViewContent)
             {
                 Destroy(child.gameObject);
             }
         }
 
         public void BuyOnClick()
         {
             Item purchasedItem = MerchantInventory.ClothingItems.Find(x => x.Name.Equals(EventSystem.current.currentSelectedGameObject.transform.parent.parent.Find("Name").GetComponent<Text>().text));
 
             if (purchasedItem == null)
             {
                 Debug.Log("Unable To Find Item In Database");
                 return;
             }
             else if (purchasedItem.PurchasePriceInPound() >= _playerInventoryUI.PlayerInventory.PoundCoins)
             {
                 Debug.Log("Cannot Afford Item");
                 return;
             }
 
             _playerInventoryUI.PurchaseItem(purchasedItem);
 
             MerchantInventory.ClothingItems.Remove(purchasedItem);
 
             PopulateInventory(MerchantInventory);
         }
         
     }
 }

Answer 1

Hi,

that's a good question. Randomly pick one item from a list is easy. You can simply do something like :

 myListOfItems[Random.Range(0, myListOfItems.Length)] // if it's an array
 myListOfItems[Random.Range(0, myListOfItems.Count)] // if it's a List

But picking a given number of items from a list is a bit more interesting.

Let me give this a try and explain through it. Let's begin with the method signature (our goal).

 public static List<T> GetRandomItemsFromList<T> (List<T> list, int number)

This will be a generic method, with type T so that it can work with a list of anything. It will take a list, and a number of items to pick for parameters. Then, we want to duplicate the input list, so that we can remove items from it as we add them to a new list. Eventually, we want to return the new list.

 // this is the list we're going to remove picked items from
 List<T> tmpList = new List<T>(list);
 // this is the list we're going to move items to
 List<T> newList = new List<T>();
 return newList;

Now we want to loop and move items from one list to the other.

 // make sure tmpList isn't already empty
 while (newList.Count < number && tmpList.Count > 0)
 {
     int index = Random.Range(0, tmpList.Count);
     newList.Add(tmpList[index]);
     tmpList.RemoveAt(index);
 }

So, here's the whole method :

 public static List<T> GetRandomItemsFromList<T> (List<T> list, int number)
 {
     // this is the list we're going to remove picked items from
     List<T> tmpList = new List<T>(list);
     // this is the list we're going to move items to
     List<T> newList = new List<T>();
 
     // make sure tmpList isn't already empty
     while (newList.Count < number && tmpList.Count > 0)
     {
         int index = Random.Range(0, tmpList.Count);
         newList.Add(tmpList[index]);
         tmpList.RemoveAt(index);
     }
 
     return newList;
 }

And this is how to use it :

 List<Item> randomItems = GetRandomItemsFromList<Item> (allItems, 5);

Hope this helps you figure this out.

Choose random prefabs from list?

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