ConditionalPropertyAttributes.cs

// Description: Unity 'EnableIf' and 'ShowIf' property attributes.
//
// Updated: 2020-05-16

/* MIT License
 *
 * Copyright (c) 2021 Jonatan Johansson
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

using System;
using System.Reflection;
using UnityEditor;
using UnityEngine;
using Object = UnityEngine.Object;

public abstract class ConditionalPropertyAttribute : PropertyAttribute {
	/// <summary>The name of the field to use.</summary>
	public string Reference { get; }

	/// <summary>The value to compare against.</summary>
	public object Comparand { get; }

	/// <summary>Invert the condition.</summary>
	public bool Invert { get; set; }

	internal bool IsComparison { get; }

	public ConditionalPropertyAttribute(string reference) {
		Reference = reference;
	}

	public ConditionalPropertyAttribute(string reference, object comparand) {
		Reference = reference;
		Comparand = comparand;
		IsComparison = true;
	}
}

/// <summary>
/// Disables a serialized field in the inspector if a certain condition evaluates to false. The condition can be
/// inverted with <see cref="ConditionalPropertyAttribute.Invert"/>.
/// </summary>
public class EnableIfAttribute : ConditionalPropertyAttribute {
	/// <summary>
	/// Disable the serialized field in the inspector unless the field with the name specified by <paramref name="reference"/>
	/// contains a truthy value.
	/// </summary>
	/// <param name="reference">The name of the reference field.</param>
	/// <remarks>
	/// 	<para>A value is considered truthy if it is neither null nor 0.</para>
	/// 	<para>The referenced field must be accessible from within the type in which the attribute is used.</para>
	/// </remarks>
	public EnableIfAttribute(string reference) : base(reference) { }

	/// <summary>
	/// Disable the serialized field in the inspector unless the value contained in the reference field is equal to
	/// <paramref name="comparand"/>.
	/// </summary>
	/// <param name="reference">The name of the reference field.</param>
	/// <param name="comparand">The value to compare against.</param>
	/// <remarks>
	/// 	<para>The referenced field must be accessible from within the type in which the attribute is used.</para>
	/// </remarks>
	public EnableIfAttribute(string reference, object comparand) : base(reference, comparand) { }
}

/// <summary>
/// Hide a serialized field in the inspector if a certain condition evaluates to false. The condition can be
/// inverted with <see cref="ConditionalPropertyAttribute.Invert"/>.
/// </summary>
public class ShowIfAttribute : ConditionalPropertyAttribute {
	/// <summary>
	/// Hide the serialized field in the inspector unless the field with the name specified by <paramref name="reference"/>
	/// contains a truthy value.
	/// </summary>
	/// <param name="reference">The name of the reference field.</param>
	/// <remarks>
	/// 	<para>A value is considered truthy if it is neither null nor 0.</para>
	/// 	<para>The referenced field must be accessible from within the type in which the attribute is used.</para>
	/// </remarks>
	public ShowIfAttribute(string reference) : base(reference) { }

	/// <summary>
	/// Hide the serialized field in the inspector unless the value contained in the reference field is equal to
	/// <paramref name="comparand" />.
	/// </summary>
	/// <param name="reference">The name of the reference field.</param>
	/// <param name="comparand">The value to compare against.</param>
	/// <remarks>
	/// 	<para>The referenced field must be accessible from within the type in which the attribute is used.</para>
	/// </remarks>
	public ShowIfAttribute(string reference, object comparand) : base(reference, comparand) { }
}


#if UNITY_EDITOR
namespace PropertyDrawers {
	[CustomPropertyDrawer(typeof(ConditionalPropertyAttribute), true)]
	public class ConditionalPropertyDrawer : PropertyDrawer {
		private const int HelpBoxPadding = 2;
		private const int HelpBoxMinHeight = 38; // Magic constant.

		private Type cachedReferenceFieldType;
		private FieldInfo cachedReferenceField;
		private bool cachedReferenceFieldStatic;

		private bool ok;
		private bool needsUpdate;
		private bool conditionResult;
		private string errorMessage;

		private float propHeight;

		public override bool CanCacheInspectorGUI(SerializedProperty property) {
			return false; // Probably not?
		}

		public override float GetPropertyHeight(SerializedProperty property, GUIContent label) {
			EvaluateCondition(property);

			if (ok && attribute is ShowIfAttribute && !conditionResult)
				return 0f; // Hidden.

			float height = propHeight = EditorGUI.GetPropertyHeight(property, label, true);
			if (!ok && errorMessage != null)
				height += HelpBoxPadding + Mathf.Max(HelpBoxMinHeight,
				                                     EditorStyles.helpBox.CalcHeight(
				                                         new GUIContent(errorMessage),
				                                         EditorGUIUtility.currentViewWidth));

			return height;
		}

		public override void OnGUI(Rect position, SerializedProperty property, GUIContent label) {
			if (needsUpdate) {
				Debug.Assert(false, "GetPropertyHeight did not execute before OnGUI.");
				EvaluateCondition(property);
			}

			needsUpdate = true;

			if (ok) {
				if (attribute is EnableIfAttribute) {
					EditorGUI.BeginDisabledGroup(!conditionResult);
					EditorGUI.PropertyField(position, property, label, true);
					EditorGUI.EndDisabledGroup();
					return;
				}
				if (attribute is ShowIfAttribute && !conditionResult)
					return; // Hidden.
			}
			else {
				if (errorMessage != null) {
					EditorGUI.PropertyField(position, property, label, true);
					position.yMin += HelpBoxPadding + propHeight;
					EditorGUI.HelpBox(position, errorMessage, MessageType.Error);
					return;
				}
			}

			// Fallback to default drawer.
			EditorGUI.PropertyField(position, property, label, true);
		}

		private void EvaluateCondition(SerializedProperty property) {
			ConditionalPropertyAttribute attr = attribute as ConditionalPropertyAttribute;

			ok = false;
			errorMessage = null;
			needsUpdate = false;

			// Validate
			if (attr == null) return;
			if (attr.Reference == null) {
				errorMessage = "Field reference is null.";
				return;
			}

			SerializedObject serializedObject = property.serializedObject;
			// Show default when multi editing objects.
			if (serializedObject.isEditingMultipleObjects) return;

			Object target = serializedObject.targetObject;
			if (target == null) return;

			// Find the reference field
			Type declType = fieldInfo.DeclaringType;
			Debug.Assert(declType != null);
			if (cachedReferenceField == null) {
				cachedReferenceField = declType.GetField(attr.Reference,
				                                         BindingFlags.Public | BindingFlags.NonPublic |
				                                         BindingFlags.Instance | BindingFlags.Static);

				if (cachedReferenceField == null) {
					errorMessage = $"No field named '{attr.Reference}' found in type '{declType.Name}'.";
					return;
				}

				cachedReferenceFieldType = cachedReferenceField.FieldType;
				cachedReferenceFieldStatic = cachedReferenceField.IsStatic;
			}

			// Check the condition
			object value = cachedReferenceField.GetValue(cachedReferenceFieldStatic ? null : target);
			bool result = attr.IsComparison
				? Equals(value, attr.Comparand)
				: IsTruthy(value, cachedReferenceFieldType);

			// Store the result
			conditionResult = attr.Invert ? !result : result;
			ok = true;
		}

		/// <summary>
		/// Check if a value is considered truthy.
		/// </summary>
		private static bool IsTruthy(object value, Type type) {
			if (type.IsValueType && value is IConvertible convertible) {
				TypeCode typeCode = convertible.GetTypeCode();
				if (typeCode == TypeCode.Object || typeCode == TypeCode.DateTime)
					return true;

				// All numbers are convertible to double
				try { return convertible.ToDouble(null) != 0.0; }
				catch { /* ignored */ }
			}

			return value != null && !value.Equals(null);
		}
	}
}
#endif