From 55735b4c6448fa4373d4beaa91754503f91018f8 Mon Sep 17 00:00:00 2001
From: Ellpeck <me@ellpeck.de>
Date: Tue, 13 Sep 2022 14:27:49 +0200
Subject: [PATCH] Added Element.OnAddedToUi and Element.OnRemovedFromUi

---
 CHANGELOG.md                |  1 +
 MLEM.Ui/Elements/Element.cs | 14 ++++++++++++--
 MLEM.Ui/UiSystem.cs         |  2 ++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d8dda3e..8d505d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@ Fixes
 Additions
 - Added some extension methods for querying Anchor types
 - Added Element.AutoSizeAddedAbsolute to allow for more granular control of auto-sizing
+- Added Element.OnAddedToUi and Element.OnRemovedFromUi
 
 Improvements
 - Allow elements to auto-adjust their size even when their children are aligned oddly
diff --git a/MLEM.Ui/Elements/Element.cs b/MLEM.Ui/Elements/Element.cs
index ccf3748..4e168f0 100644
--- a/MLEM.Ui/Elements/Element.cs
+++ b/MLEM.Ui/Elements/Element.cs
@@ -407,14 +407,22 @@ namespace MLEM.Ui.Elements {
         /// </summary>
         public GamepadNextElementCallback GetGamepadNextElement;
         /// <summary>
-        /// Event that is called when a child is added to this element using <see cref="AddChild{T}"/>
+        /// Event that is called when a child or any level of grandchild is added to this element using <see cref="AddChild{T}"/>
         /// </summary>
         public OtherElementCallback OnChildAdded;
         /// <summary>
-        /// Event that is called when a child is removed from this element using <see cref="RemoveChild"/>
+        /// Event that is called when a child or any level of grandchild is removed from this element using <see cref="RemoveChild"/>
         /// </summary>
         public OtherElementCallback OnChildRemoved;
         /// <summary>
+        /// Event that is called when this element is added to a <see cref="UiSystem"/>, that is, when this element's <see cref="System"/> is set to a non-<see langword="null"/> value.
+        /// </summary>
+        public GenericCallback OnAddedToUi;
+        /// <summary>
+        /// Event that is called when this element is removed from a <see cref="UiSystem"/>, that is, when this element's <see cref="System"/> is set to <see langword="null"/>.
+        /// </summary>
+        public GenericCallback OnRemovedFromUi;
+        /// <summary>
         /// Event that is called when this element's <see cref="Dispose"/> method is called, which also happens in <see cref="Finalize"/>.
         /// This event is useful for unregistering global event handlers when this object should be destroyed.
         /// </summary>
@@ -497,6 +505,7 @@ namespace MLEM.Ui.Elements {
             element.AndChildren(e => {
                 e.Root = this.Root;
                 e.System = this.System;
+                e.OnAddedToUi?.Invoke(e);
                 this.Root?.InvokeOnElementAdded(e);
                 this.OnChildAdded?.Invoke(this, e);
             });
@@ -520,6 +529,7 @@ namespace MLEM.Ui.Elements {
             element.AndChildren(e => {
                 e.Root = null;
                 e.System = null;
+                e.OnRemovedFromUi?.Invoke(e);
                 this.Root?.InvokeOnElementRemoved(e);
                 this.OnChildRemoved?.Invoke(this, e);
             });
diff --git a/MLEM.Ui/UiSystem.cs b/MLEM.Ui/UiSystem.cs
index 2f4fd32..b9d78e7 100644
--- a/MLEM.Ui/UiSystem.cs
+++ b/MLEM.Ui/UiSystem.cs
@@ -347,6 +347,7 @@ namespace MLEM.Ui {
             root.Element.AndChildren(e => {
                 e.Root = root;
                 e.System = this;
+                e.OnAddedToUi?.Invoke(e);
                 root.InvokeOnElementAdded(e);
                 e.SetAreaDirty();
             });
@@ -369,6 +370,7 @@ namespace MLEM.Ui {
             root.Element.AndChildren(e => {
                 e.Root = null;
                 e.System = null;
+                e.OnRemovedFromUi?.Invoke(e);
                 root.InvokeOnElementRemoved(e);
                 e.SetAreaDirty();
             });