Add NavigationStack script

Author: adamgraham

Runtime/NavigationStack.cs

@@ -0,0 +1,82 @@
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.EventSystems;
+using UnityEngine.InputSystem;
+
+namespace Zigurous.UI
+{
+    [RequireComponent(typeof(EventSystem))]
+    [AddComponentMenu("Zigurous/UI/Navigation/Navigation Stack")]
+    public class NavigationStack : MonoBehaviour
+    {
+        public EventSystem eventSystem { get; private set; }
+        public Stack<GameObject> navigationStack { get; private set; }
+        public GameObject CurrentSelectedGameObject => this.navigationStack.Peek();
+        public InputAction backInput;
+        public bool allowEmptyStack = false;
+        public bool allowNullSelections = false;
+
+        private void Reset()
+        {
+            this.backInput = new InputAction("MenuBackNavigation", InputActionType.Button);
+            this.backInput.AddBinding("<Keyboard>/escape");
+            this.backInput.AddBinding("<Keyboard>/backspace");
+            this.backInput.AddBinding("<Gamepad>/select");
+            this.backInput.AddBinding("<Gamepad>/buttonEast");
+        }
+
+        private void Awake()
+        {
+            this.eventSystem = GetComponent<EventSystem>();
+            this.navigationStack = new Stack<GameObject>(8);
+        }
+
+        private void OnEnable()
+        {
+            this.backInput.Enable();
+            this.backInput.performed += OnBack;
+        }
+
+        private void OnDisable()
+        {
+            this.backInput.Disable();
+            this.backInput.performed -= OnBack;
+        }
+
+        private void Update()
+        {
+            if (this.eventSystem.currentSelectedGameObject != CurrentSelectedGameObject)
+            {
+                if (this.eventSystem.currentSelectedGameObject != null || this.allowNullSelections) {
+                    this.navigationStack.Push(this.eventSystem.currentSelectedGameObject);
+                }
+            }
+        }
+
+        public void Back()
+        {
+            if (this.navigationStack.Count == 0) {
+                return;
+            }
+
+            if (this.navigationStack.Count > 1 || this.allowEmptyStack) {
+                this.navigationStack.Pop();
+            }
+
+            this.eventSystem.SetSelectedGameObject(null);
+
+            if (this.navigationStack.Count > 0) {
+                this.eventSystem.SetSelectedGameObject(this.navigationStack.Peek());
+            }
+        }
+
+        private void OnBack(InputAction.CallbackContext context)
+        {
+            if (context.performed) {
+                Back();
+            }
+        }
+
+    }
+
+}