How does one access the Label argument of a PropertyField within a PropretyDrawer using UIToolkit/UIElements?

Hey @craftsmanbeck,

It does appear that the label argument to the PropertyField constructor is ignored during CreateInspectorGUI when using a custom property drawer with UIElements. However, I have found a bit of a hack workaround using EditorCoroutineUtility.StartCoroutine. You can install the EditorCoroutine package via Window -> Package Manager. Be sure to check Advanced -> Show Preview Packages.

Below is an example that demonstrates the problem of not being able to set the labels as well as a solution. It uses the Recipe/Ingredient data structure from https://docs.unity3d.com/ScriptReference/PropertyDrawer.html. Here's a screenshot of the resulting UI (note the custom labels):

Assets/Recipe.cs

 // From the example at https://docs.unity3d.com/ScriptReference/PropertyDrawer.html
 using System;
 using UnityEngine;
 
 public enum IngredientUnit { Spoon, Cup, Bowl, Piece }
 
 // Custom serializable class
 [Serializable]
 public class Ingredient
 {
     public string name;
     public int amount = 1;
     public IngredientUnit unit;
 }
 
 public class Recipe : MonoBehaviour
 {
     public Ingredient potionResult;
     public Ingredient[] potionIngredients;
 }

Assets/Editor/IngredientDrawer.cs

 using UnityEditor;
 using UnityEditor.UIElements;
 using UnityEngine.UIElements;
 
 [CustomPropertyDrawer(typeof(Ingredient))]
 public class IngredientDrawer : PropertyDrawer
 {
     public override VisualElement CreatePropertyGUI(SerializedProperty property)
     {
         // NOTE: This gets called when you call `ui.Bind()` in `RecipeEditor.cs`,
         //       but also gets called again automatically afterwards, which seems
         //       to be what's blowing away the changes to the labels.
         //Debug.Log($"[IngredientDrawer.CreatePropertyGUI] - {property.displayName}"); // For tracing
 
         var container = new VisualElement();
 
         // NOTE: These 3 `label` arguments work fine
         var amountField = new PropertyField(property.FindPropertyRelative("amount"), "Amount (arg)");
         var unitField = new PropertyField(property.FindPropertyRelative("unit"), "Unit (arg)");
         var nameField = new PropertyField(property.FindPropertyRelative("name"), "Name (arg)");
 
         container.Add(amountField);
         container.Add(unitField);
         container.Add(nameField);
 
         return container;
     }
 }

Assets/Editor/IngredientDrawer.cs

 using System.Collections;
 using Unity.EditorCoroutines.Editor;
 using UnityEditor;
 using UnityEditor.UIElements;
 using UnityEngine;
 using UnityEngine.UIElements;
 
 [CustomEditor(typeof(Recipe))]
 public class RecipeEditor : Editor
 {
     PropertyField resultField;
     PropertyField ingredientsField;
 
     public override VisualElement CreateInspectorGUI()
     {
         //Debug.Log($"[RecipeEditor.CreateInspectorGUI] - BEGIN"); // For tracing
 
         var ui = new VisualElement();
 
         // NOTE: The `label` arguments, "Result (arg)" and "Ingredients (arg)", seem to be ignored.
         //resultField = new PropertyField(serializedObject.FindProperty("potionResult"), "Result (arg)");
         //ingredientsField = new PropertyField(serializedObject.FindProperty("potionIngredients"), "Ingredients (arg)");
 
         // NOTE: Setting the `label` property after creating the fields also doesn't work.
         //resultField.label = "Result (set prop)";
         //ingredientsField.label = "Test Ingredients (set prop)";
 
         resultField = new PropertyField(serializedObject.FindProperty("potionResult"));
         ingredientsField = new PropertyField(serializedObject.FindProperty("potionIngredients"));
         ui.Add(resultField);
         ui.Add(ingredientsField);
 
         // Calling `Bind` actually fleshes out the PropertyFields above, but it doesn't matter,
         // since the fields get overwritten later, so setting the labels after this still won't work.
         ////Debug.Log(ingredientsField.childCount); // 0
         //ui.Bind(serializedObject);
         ////Debug.Log(ingredientsField.childCount); // 1 -- doesn't matter
 
 
         // HOWEVER!! Setting the labels in a coroutine later does work!!
         EditorCoroutineUtility.StartCoroutine(InitializeUICoroutine(), this);
         EditorCoroutineUtility.StartCoroutine(RefreshUICoroutine(), this);
 
         //Debug.Log($"[RecipeEditor.CreateInspectorGUI] - END"); // For tracing
 
         return ui;
     }
 
     void InitializeUI()
     {
         // Static labels (not dynamic list/array)
         // OPTION: Create and insert a new label
         resultField.Insert(0, new Label("Result (coroutine)"));
     }
 
     void RefreshUI()
     {
         //Debug.Log($"[RecipeEditor.UpdateLabels]"); // For tracing
 
         // OPTION: Find and edit an existing label
         var foldout = ingredientsField.Q<Foldout>("unity-foldout-potionIngredients");
         foldout.text = "Potion Ingredients (coroutine)";
 
         // Alternative quick-n-dirty way to do the above since we know it's the first label
         //ingredientsField.Q<Label>().text = "Potion Ingredients (coroutine2)";
 
         // Another example of finding and editing an existing label
         var sizeField = ingredientsField.Q<IntegerField>("unity-input-potionIngredients.Array.size");
         sizeField.label = "Size (coroutine)";
 
         // Really hacky way to set a label's text, if you know the exact child layout (FRAGILE!)
         //((Label)ingredientsField[0][0][0][0]).text = "Size (coroutine2)";
 
         // New size field needs a new event handler
         sizeField.RegisterCallback<BlurEvent>(HandleSizeFieldBlur);
     }
 
     IEnumerator InitializeUICoroutine()
     {
         yield return new WaitForSecondsRealtime(0.067f);
         InitializeUI();
     }
 
     IEnumerator RefreshUICoroutine()
     {
         yield return new WaitForSecondsRealtime(0.067f);
         RefreshUI();
     }
 
     void HandleSizeFieldBlur(BlurEvent evt)
     {
         EditorCoroutineUtility.StartCoroutine(RefreshUICoroutine(), this);
     }
 
 }

And here's a screenshot of when I was using the UIElements debugger to find the structure of the UI:

Note: tested with Unity version 2019.3.13f1 and 2020.1.0b3

Hope this helps!