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Assets/Plugins/Animancer/Internal/Editor/GUI/DummySerializableCallback.cs

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+// Animancer // https://kybernetik.com.au/animancer // Copyright 2018-2023 Kybernetik //
+
+#if UNITY_EDITOR
+
+#pragma warning disable CS0649 // Field is never assigned to, and will always have its default value.
+
+using UnityEditor;
+using UnityEngine;
+using UnityEngine.Events;
+
+namespace Animancer.Editor
+{
+    /// <summary>
+    /// An object that holds a serialized callback (a <see cref="UnityEvent"/> by default) so that empty ones can be
+    /// drawn in the GUI without allocating array space for them until they actually contain something.
+    /// </summary>
+    internal class DummySerializableCallback : ScriptableObject
+    {
+        /************************************************************************************************************************/
+
+        [SerializeField] private SerializableCallbackHolder _Holder;
+
+        /************************************************************************************************************************/
+
+        private static SerializedProperty _CallbackProperty;
+
+        private static SerializedProperty CallbackProperty
+        {
+            get
+            {
+                if (_CallbackProperty == null)
+                {
+                    var instance = CreateInstance<DummySerializableCallback>();
+
+                    instance.hideFlags = HideFlags.HideInHierarchy | HideFlags.DontSave;
+                    var serializedObject = new SerializedObject(instance);
+                    _CallbackProperty = serializedObject.FindProperty(
+                        $"{nameof(_Holder)}.{SerializableCallbackHolder.CallbackField}");
+
+                    AssemblyReloadEvents.beforeAssemblyReload += () =>
+                    {
+                        serializedObject.Dispose();
+                        DestroyImmediate(instance);
+                    };
+                }
+
+                return _CallbackProperty;
+            }
+        }
+
+        /************************************************************************************************************************/
+
+        public static float Height => EditorGUI.GetPropertyHeight(CallbackProperty);
+
+        /************************************************************************************************************************/
+
+        public static bool DoCallbackGUI(ref Rect area, GUIContent label, SerializedProperty property,
+            out object callback)
+        {
+            var callbackProperty = CallbackProperty;
+            callbackProperty.serializedObject.Update();
+            callbackProperty.prefabOverride = property.prefabOverride;
+
+            area.height = Height;
+
+            EditorGUI.BeginChangeCheck();
+            label = EditorGUI.BeginProperty(area, label, property);
+
+            // UnityEvents ignore the proper indentation which makes them look terrible in a list.
+            // So we force the area to be indented.
+            var indentedArea = EditorGUI.IndentedRect(area);
+            var indentLevel = EditorGUI.indentLevel;
+            EditorGUI.indentLevel = 0;
+
+            EditorGUI.PropertyField(indentedArea, callbackProperty, label, false);
+
+            EditorGUI.indentLevel = indentLevel;
+
+            EditorGUI.EndProperty();
+            if (EditorGUI.EndChangeCheck())
+            {
+                callbackProperty.serializedObject.ApplyModifiedProperties();
+                callback = callbackProperty.GetValue();
+
+                callbackProperty.SetValue(null);
+                callbackProperty.serializedObject.Update();
+
+                if (AnimancerEvent.Sequence.Serializable.HasPersistentCalls(callback))
+                    return true;
+            }
+
+            callback = null;
+            return false;
+        }
+
+        /************************************************************************************************************************/
+    }
+}
+
+#endif