Initial Commit

Editor/Extensions/Dropdown Field/DropdownFieldExtensions.cs

@@ -0,0 +1,130 @@
+#if UNITY_EDITOR
+
+using System;
+using System.Linq.Expressions;
+using System.Reflection;
+using UnityEditor;
+using UnityEngine.UIElements;
+
+namespace Utilities.Extensions.UIToolkit
+{
+    public static class DropdownFieldExtensions
+    {
+        private static Type genericOSMenuType;
+        private static Type iGenericMenuInterfaceType;
+
+        private const string CreateMenuCallback_Property_Name = "createMenuCallback";
+        private const string GenericOsMenu_Type_Name = "UnityEditor.UIElements.GenericOSMenu";
+        private const string IGenericMenu_Type_Name = "IGenericMenu";
+
+        private const string FormatSelectedValueCallback_Property_Name = "formatSelectedValueCallback";
+
+        #region Generic Menu Assigning
+
+        public static void AssignGenericMenu(this DropdownField dropdownField, 
+            Func<GenericMenu> genericMenuBuildingFunc)
+        {
+            Func<object> genericOSMenuFunc = () =>
+            {
+                GenericMenu menu = genericMenuBuildingFunc();
+                return GetGenericOSMenu(menu);
+            };
+
+            object boxedfunc = ConvertFuncToDesiredType(genericOSMenuFunc);
+
+            FieldInfo createMenuCallbackFieldInfo = typeof(DropdownField)
+                .GetField(CreateMenuCallback_Property_Name, BindingFlags.FlattenHierarchy | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
+
+            createMenuCallbackFieldInfo.SetValue(dropdownField, boxedfunc);
+        }
+
+        #region Generic OS Menu Creation
+
+        private static object GetGenericOSMenu(GenericMenu menu)
+        {
+            Type type = GetGenericOSMenuType();
+            object[] args = new object[] { menu };
+            return Activator.CreateInstance(type, args);
+        }
+
+        #endregion
+
+        #region Type helpers
+
+        private static Type GetGenericOSMenuType()
+        {
+            if (genericOSMenuType == null)
+            {
+                genericOSMenuType = typeof(UnityEditor.UIElements.ColorField).Assembly.GetType(GenericOsMenu_Type_Name, false, true);
+            }
+
+            return genericOSMenuType;
+        }
+
+        private static Type GetIGenericMenuInterfaceType()
+        {
+            if (iGenericMenuInterfaceType == null)
+            {
+                Type genericOSType = GetGenericOSMenuType();
+                iGenericMenuInterfaceType = genericOSType.GetInterface(IGenericMenu_Type_Name);
+            }
+
+            return iGenericMenuInterfaceType;
+        }
+
+        #endregion
+
+        #region Func Conversion
+
+        private static Delegate ConvertFuncToDesiredType(Func<object> func)
+        {
+            Type interfaceType = GetIGenericMenuInterfaceType();
+            Type resultType = typeof(Func<>).MakeGenericType(interfaceType);
+
+            Expression<Func<object>> expressionFunc = FuncToExpression(func);
+
+            InvocationExpression invokedExpression = Expression.Invoke(expressionFunc);
+            UnaryExpression convertedReturnValue = Expression.Convert(invokedExpression, interfaceType);
+
+            LambdaExpression lambda = Expression.Lambda(delegateType: resultType, body: convertedReturnValue);
+
+            return lambda.Compile();
+        }
+
+        private static Expression<Func<T>> FuncToExpression<T>(Func<T> f)
+        {
+            return () => f();
+        }
+
+        #endregion
+
+        #endregion
+
+        #region Formatting Callback Assigning
+
+        public static void AssignFormattingCallback(this DropdownField dropdownField, 
+            Func<string, string> formattingCallback)
+        {
+#if UNITY_2022_2_OR_NEWER
+            dropdownField.formatSelectedValueCallback = formattingCallback;
+#else
+            AssignFormattingCallbackViaReflection(dropdownField, formattingCallback);      
+#endif
+        }
+
+        private static void AssignFormattingCallbackViaReflection(this DropdownField functionDropdown, 
+            Func<string, string> formattingCallback)
+        {
+            PropertyInfo propertyInfo = typeof(DropdownField)
+                .GetProperty(FormatSelectedValueCallback_Property_Name, BindingFlags.FlattenHierarchy | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
+
+            object[] args = new object[] { formattingCallback };
+
+            propertyInfo.SetMethod.Invoke(functionDropdown, args);
+        }
+
+        #endregion
+    }
+}
+
+#endif