Cannot query for an element, returns null.

I managed to use C# to create additional items and append them, but not remove them, clone them or store them. The creation and appending has succeeded, so the connection between C# script and UXML is valid (no crazy lack of references)

Code:

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.UIElements;
3.  
4.  
5. namespace UITEST
6. {
7.     public class CompProc : MonoBehaviour
8.     {
9.  
10.         UIDocument doc;
11.         VisualElement root;
12.         VisualElement prefab;
13.      
14.  
15.         void Start()
16.         {
17.             doc = GetComponent<UIDocument>();
18.             root = doc.rootVisualElement;
19.  
20.  
21.             // This works. So the UXML works.
22.             var newBox = new UnityEngine.UIElements.Box();
23.             var newLabel = new UnityEngine.UIElements.Label("Holy smokes batman!");
24.             newBox.Add(newLabel);
25.             root.Add(newBox);
26.  
27.          
28.             // This returns null, why?
29.             prefab = root.Q<UnityEngine.UIElements.Button>("prefab");
30.             Debug.Log(prefab); // Null
31.          
32.          
33.             // How do I clone
34.             for (int i = 0; i < 10; i++)
35.             {
36.                 //root.Append("dataHolder", buttonPrefab) ??????
37.             }
38.  
39.          
40.             // How do I remove an object?
41.             var remBtn = root.Q<UnityEngine.UIElements.Box>("remBtn");
42.             root.Remove(remBtn);
43.             // ArgumentException: Cannot remove null child
44.          
45.         }
46.  
47.     }
48. }
49.  

And UXML:

Code (CSharp):

1. <ui:UXML xmlns:ui="UnityEngine.UIElements" xmlns:uie="UnityEditor.UIElements" editor-extension-mode="False">
2.     <Style src="test.uss" />
3.     <ui:Box class="dataHolder">
4.         <ui:Button text="New Button" name="button" class="prefab" />
5.         <ui:Button text="RemBtn" name="button" class="remBtn" />
6.     </ui:Box>
7. </ui:UXML>
8.  

Note: I really really don't like UI Builder and I would really really focus on the C# approach to dynamically remove/add things.

 

I had an entire paragraph here which I deleted because it seems to have vanished. When you edit UXML script, under certain conditions, UIBuilder will popup for no reason. Closing it doesn't help, uninstalling it breaks UIToolkit. Thats my remaining issue, it has to be installed, it popups without request and cannot be removed and isn't worked in.

Two other things which happened to me but aren't true anymore are that UIBuilder would throw an error saying "do not edit files externally, because it could cause data loss" and that you couldn't unset width of an element (to go 'width: auto') because as soon as you added another element, it would still forcibly apply a fixed size of 450px which wasn't present in code. But they are gone for now.

Other than that props to UIToolkit developers at Unity. Making UI is finally not a burden.

--

The remove part threw:

ArgumentException: This visualElement is not my child

from code:

Code (CSharp):

1. var remBtn = root.Q<UnityEngine.UIElements.Button>(className: "remBtn");
2.             Debug.Log(remBtn);
3.             root.Remove(remBtn);

I'll try to getting closer in hierarchy and then select the object.

edit3:

This works:

Code (CSharp):

1.  
2.             var dataHolder = root.Q<UnityEngine.UIElements.Box>(className: "dataHolder");
3.             var remBtn = dataHolder.Q<UnityEngine.UIElements.Button>(className: "remBtn");
4.            
5.             Debug.Log(remBtn);
6.             dataHolder.Remove(remBtn);

You actually have to go to the parent of that object.