Merge pull request #9 from Thundernerd/feature/drag_and_drop

Feature/drag and drop

Author: Thundernerd

Editor/Drawers/RawReferenceDrawer.cs

@@ -69,6 +69,8 @@ public void OnGUI(Rect position)
                 RawReferenceProperty,
                 new GUIContent(rawReferenceValue.GetType().Name),
                 true);
+
+            HandleDragAndDrop(objectFieldRect);
         }
 
         /// <inheritdoc />

Editor/Drawers/ReferenceDrawer.cs

@@ -1,15 +1,26 @@
 using System;
+using System.Linq;
 using TNRD.Utilities;
 using UnityEditor;
 using UnityEditor.IMGUI.Controls;
 using UnityEngine;
+using UnityEngine.Assertions;
 using UnityEngine.SceneManagement;
 using Object = UnityEngine.Object;
 
 namespace TNRD.Drawers
 {
     internal abstract class ReferenceDrawer
     {
+        private enum DragAndDropMode
+        {
+            None,
+            Raw,
+            Unity
+        }
+
+        private DragAndDropMode dragAndDropMode;
+
         protected readonly SerializedProperty Property;
         protected readonly Type GenericType;
         protected readonly CustomObjectDrawer CustomObjectDrawer;
@@ -95,5 +106,94 @@ private void OnItemSelected(ReferenceMode mode, object reference)
         }
 
         protected abstract void OnPropertiesClicked();
+
+        protected void HandleDragAndDrop(Rect position)
+        {
+            if (Event.current.type == EventType.DragPerform)
+            {
+                HandleDragPerform();
+            }
+            else if (Event.current.type == EventType.DragUpdated)
+            {
+                HandleDragUpdated(position);
+            }
+        }
+
+        private void SetDragAndDropMode(bool success, DragAndDropMode? successMode = null)
+        {
+            if (success)
+            {
+                Assert.IsTrue(successMode.HasValue);
+                dragAndDropMode = successMode.Value;
+                DragAndDrop.visualMode = DragAndDropVisualMode.Link;
+            }
+            else
+            {
+                dragAndDropMode = DragAndDropMode.None;
+                DragAndDrop.visualMode = DragAndDropVisualMode.Rejected;
+            }
+        }
+
+        private void HandleDragUpdated(Rect position)
+        {
+            if (!position.Contains(Event.current.mousePosition))
+                return;
+
+            if (DragAndDrop.objectReferences.Length > 1)
+            {
+                SetDragAndDropMode(false);
+                return;
+            }
+
+            Object objectReference = DragAndDrop.objectReferences[0];
+
+            if (objectReference is GameObject gameObject)
+            {
+                Component component = gameObject.GetComponent(GenericType);
+                SetDragAndDropMode(component != null, DragAndDropMode.Unity);
+            }
+            else if (objectReference is MonoScript monoScript)
+            {
+                Type scriptType = monoScript.GetClass();
+
+                if (scriptType.IsSubclassOf(typeof(UnityEngine.Object)))
+                {
+                    SetDragAndDropMode(false);
+                    return;
+                }
+                
+                if (!GenericType.IsAssignableFrom(scriptType))
+                {
+                    SetDragAndDropMode(false);
+                    return;
+                }
+
+                bool isValidDrop = scriptType.GetConstructors().Any(x => x.GetParameters().Length == 0);
+                SetDragAndDropMode(isValidDrop, DragAndDropMode.Raw);
+            }
+            else
+            {
+                SetDragAndDropMode(GenericType.IsInstanceOfType(objectReference), DragAndDropMode.Unity);
+            }
+        }
+
+        private void HandleDragPerform()
+        {
+            switch (dragAndDropMode)
+            {
+                case DragAndDropMode.Raw:
+                    RawReferenceProperty.managedReferenceValue =
+                        Activator.CreateInstance(((MonoScript)DragAndDrop.objectReferences[0]).GetClass());
+                    ReferenceModeProperty.enumValueIndex = (int)ReferenceMode.Raw;
+                    break;
+                case DragAndDropMode.Unity:
+                    UnityReferenceProperty.objectReferenceValue = DragAndDrop.objectReferences[0];
+                    ReferenceModeProperty.enumValueIndex = (int)ReferenceMode.Unity;
+                    break;
+                case DragAndDropMode.None:
+                default:
+                    throw new ArgumentOutOfRangeException();
+            }
+        }
     }
 }

Editor/Drawers/UnityReferenceDrawer.cs

@@ -27,6 +27,7 @@ public void OnGUI(Rect position)
             Type referenceType = unityReference == null ? typeof(Object) : unityReference.GetType();
             GUIContent objectContent = EditorGUIUtility.ObjectContent(unityReference, referenceType);
             CustomObjectDrawer.OnGUI(position, label, objectContent);
+            HandleDragAndDrop(position);
         }
 
         protected override void OnPropertiesClicked()