When working with different kinds of pickups, one approach is to use a C# List to maintain a flexible-length data structure of the items currently in the inventory. In this recipe, we will show you how, each time an item is picked up, a new object is added to such a List collection. An iteration through the List is how the text display of items is generated each time the inventory changes. We introduce a very simple PickUp script class, demonstrating how information about a pickup can be stored in a scripted component, extracted upon collision, and stored in our List.
This recipe assumes that you are starting with the project Simple2Dgame_SpaceGirl setup from the first recipe in this chapter. The font you need can be found in the 1362_02_02 folder.
To display inventory total text for multiple pickups of different object types, follow these steps:
- Start with a new copy of the mini-game
Simple2Dgame_SpaceGirl. - Edit the tags, changing tag Star to Pickup. Ensure that the
starGameObject now has the tag Pickup. - Add the following C# Script
PickUpto GameObjectstarin the Hierarchy:using UnityEngine; using System.Collections; public class PickUp : MonoBehaviour { public string description; } - In the Inspector, change the description property of component Pick Up (Script) of GameObject
starto the textstar, as shown in the following screenshot:
- Select the GameObject
starin the Hierarchy panel and make a copy of this GameObject, renaming the copyheart. - In the Inspector, change the description property of component Pick Up (Script) of GameObject
heartto the textheart. Also, drag from the Project panel (folderSprites) image healthheart into the Sprite property of GameObjectheart. The player should now see the heart image on screen for this pickup item. - Select the GameObject
starin the Hierarchy panel and make a copy of this GameObject, renaming the copykey. - In the Inspector, change the description property of component Pick Up (Script) of GameObject
keyto the textkey.Also, drag from the Project panel (folder Sprites) image icon_key_green_100 into the Sprite property of GameObjectkey. The player should now see the key image on screen for this pickup item. - Make another one or two copies of each pickup GameObject and arrange them around the screen, so there are two or three each of star, heart, and key pickup GameObjects.
- Add the following C# Script
Playerto GameObjectplayer-SpaceGirlin the Hierarchy:using UnityEngine; using System.Collections; using UnityEngine.UI; using System.Collections.Generic; public class Player : MonoBehaviour { private PlayerInventoryDisplay playerInventoryDisplay; private List<PickUp> inventory = new List<PickUp>(); void Start(){ playerInventoryDisplay = GetComponent<PlayerInventoryDisplay>(); playerInventoryDisplay.OnChangeInventory(inventory); } void OnTriggerEnter2D(Collider2D hit){ if(hit.CompareTag("Pickup")){ PickUp item = hit.GetComponent<PickUp>(); inventory.Add( item ); playerInventoryDisplay.OnChangeInventory(inventory); Destroy(hit.gameObject); } } } - Add a UI Text object (Create | UI | Text). Rename it
Text-inventory-list. Change its text to the quick brown fox jumped over the lazy dog the quick brown fox jumped over the lazy dog, or another long list of nonsense words, to test the overflow settings you change in the next step. - In the Text (Script) component, ensure that Horizontal Overflow is set to Wrap, and set Vertical Overflow to Overflow—this will ensure that the text will wrap onto a second or third line (if needed) and not be hidden if there are lots of pickups.
- In the Inspector panel, set its font to Xolonium-Bold (folder
Fonts) and set its color to yellow. For the Alignment property, center the text horizontally and ensure that the text is top aligned vertically, and set the Font Size to 28 and choose a yellow text Color. - Edit its Rect Transform and set its Height to
50. Then, while holding down SHIFT and ALT (to set pivot and position), choose the top-stretch box. The text should now be positioned at the middle top of the Game panel, and its width should stretch to match that of the whole panel. - Your text should now appear at the top of the game panel.
- Add the following C# Script
PlayerInventoryDisplayto GameObjectplayer-SpaceGirlin the Hierarchy:using UnityEngine; using System.Collections; using UnityEngine.UI; using System.Collections.Generic; public class PlayerInventoryDisplay : MonoBehaviour { public Text inventoryText; public void OnChangeInventory(List<PickUp> inventory){ // (1) clear existing display inventoryText.text = ""; // (2) build up new set of items string newInventoryText = "carrying: "; int numItems = inventory.Count; for(int i = 0; i < numItems; i++){ string description = inventory[i].description; newInventoryText += " [" + description+ "]"; } if(numItems < 1) newInventoryText = "(empty inventory)"; // (3) update screen display inventoryText.text = newInventoryText; } } - From the Hierarchy view, select the GameObject
player-SpaceGirl. Then, from the Inspector, access the Player Inventory Display (Script) component and populate the Inventory Text public field with the UI Text objectText-inventory-list. - Play the game—each time you pick up a star or key or heart, the updated list of what you are carrying should be displayed in the form carrying: [key] [heart].
In the script class Player, the variable inventory is a C# List<>. This is a flexible data structure, which can be sorted, searched, and dynamically (at run time, when the game is being played) have items added to and removed from it. The <PickUp> in pointy brackets means that variable inventory will contain a list of PickUp objects. For this recipe, our PickUp class just has a single field, a string description, but we'll add more sophisticated data items in PickUp classes in later recipes.
When the scene starts, the Start() method of script class Player gets a reference to the PlayerInventoryDisplay scripted component and also initializes variable inventory to be a new, empty C# List of PickUp objects. When the OnColliderEnter2D(…) method detects collisions with items tagged Pickup, the PickUp object component of the item hit is added to our inventory list. A call is also made to the OnChangeInventory(…) method of playerInventoryDisplay to update out inventory display to the player, passing the updated inventory List as a parameter.
The script class playerInventoryDisplay has a public variable, linked to the UI Text object Text-inventory-list. The OnChangeInventory(…) method first sets the UI text to empty, and then loops through the inventory list, building up a string of each items description in square brackets ([key], [heart], and so on). If there were no items in the list, then the string is set to the text (empty inventory). Finally, the text property of the UI Text object Text-inventory-list is set to the value of this string representation of what is inside variable inventory.
Some details you don't want to miss:
It would be nice to alphabetically sort the words in the inventory list—both for neatness and consistency (so, in a game, if we pick up a key and a heart, it will look the same regardless of which order), but also so that items of the same type will be listed together, so we can easily see how many of each item we are carrying.
To implement the alphabetic sorting of the items in the inventory list, we need to do the following:
- Add the following C# code to the beginning of method
OnChangeInventory(...)in the script classPlayerInventoryDisplay:public void OnChangeInventory(List<PickUp> inventory){ inventory.Sort( delegate(PickUp p1, PickUp p2){ return p1.description.CompareTo(p2.description); } ); // rest of the method as before … } - You should now see all the items listed in alphabetic sequence. This C# code takes advantage of the
List.Sort(…)method, a feature of collections whereby each item can be compared to the next, and they are swapped if in the wrong order (if theCompareTo(…)methods returns false).