Feature Request Is there any way to access attributes bag after visual element was instantiated?

Suppose I have defined following control:

Spoiler: MyVisualElement

Code (csharp):

1.  
2. public partial class MyVisualElement : VisualElement, IBindableElement
3. {
4.     public new class UxmlFactory : UxmlFactory<MyVisualElement, UxmlTraits> { }
5.     public new class UxmlTraits : VisualElement.UxmlTraits
6.     {
7.         public override void Init(VisualElement ve, IUxmlAttributes bag, CreationContext cc)
8.         {
9.             base.Init(ve, bag, cc);
10.                
11.             bag.TryGetAttributeValue("custom-attribute", out var value);
12.         }
13.     }
14. }
15.  

I can invoke TryGetAttributeValue to access any attribute defined in uxml file inside Init method of UxmlTraits.

I would like to be able to access attributes of VisualElement which are not defined in C# with UxmlAttribute/UxmlTraits outside of custom UxmlTraits class. Something like myVisualElement.bag.TryGetAttributeValue(...).
I need this to be able to extend default behaviour of VisualElements just by adding an attribute.

Is there any chance for this feature to be implemented? Am I missing something and there is a way already?

 

You're missing something, yes. Refer to these docs: https://docs.unity3d.com/Manual/UIE-expose-custom-control-to-uxml.html

You get values from the Uxml attributes, and you can assign those values to fields/properties in the class itself, or types it inherits from. Such as so:

Code (CSharp):

1. public partial class MyVisualElement : VisualElement, IBindableElement
2. {
3.     private int _someInt;
4.    
5.     public int SomeInt => _someInt;
6.    
7.     public new class UxmlFactory : UxmlFactory<MyVisualElement, UxmlTraits> { }
8.    
9.     public new class UxmlTraits : VisualElement.UxmlTraits  
10.     {
11.         UxmlIntAttributeDescription m_someInt = new UxmlIntAttributeDescription { name = "some-int" };
12.        
13.         public override void Init(VisualElement ve, IUxmlAttributes bag, CreationContext cc)
14.         {
15.             base.Init(ve, bag, cc);
16.             var mve = (MyVisualElement)ve;
17.             mve._someInt = m_someInt.GetValueFromBag(bag, cc);
18.         }
19.     }
20. }

 

spiney199, thanks for answering, but that's not what I've asked about. I do know that it's possible to make a cusom control in C# with attributes.

I want to be able to add custom attributes through in uxml, i.e.:
<VisualElement my-custom-attribute="1234" />
and be able to read it from any other class which has access to that element

Note that I want to modify Unity's VisualElement and not my customly-declared MyVisualElement

 

griendeau_unity, I believe that I wasn't clear in my suggestion if you are giving me this answer. I'll try to clarify myself.

Suppose I have a following Text.uxml file and a MyVisualElement from first post

Spoiler: Test.uxml

Code (csharp):

1.  
2. <ui:UXML xmlns:ui="UnityEngine.UIElements" xmlns:uie="UnityEditor.UIElements" editor-extension-mode="False">
3.     <ui:VisualElement name="unityVisualElement" custom-attribute="my-custom-attribute-value"/>
4.     <MyVisualElement name="myVisualElement" custom-attribute="my-custom-attribute-value"/>
5. </ui:UXML>
6.  

I'm able to access 'custom-attribute' inside MyVisualElement's UxmlTrait.Init. Please, pay attention, that MyVisualElement does NOT have a corresponding declared attribute in C# like

Code (csharp):

1.  
2. [UxmlAttribute("custom-attribute")]
3. private String _customAttribute;
4.  

and yet, attribute 'custom-attribute' and it's value 'my-custom-attribute-value' arbitrarily defined in UXML are accessable from that Init method.

This proves that the bag (IUxmlAttributes) [or something what fills it] correctly parses UXML and collects all attributes with values defined there regardless of those attributes (not)being declared in C# control.

So my suggestion is to expose this bag as a property of a VisualElement, so it will be possible to do something like

Code (csharp):

1.  
2. unityVisualElement.bag.TryGetAttributeValue("custom-attribute", out var value);
3.  

wherever I have access to a unityVisualElement.

 

@griendeau_unity, sorry to tag you, but could you provide a follow up?

 

I think it is impossible to have access to bag at runtime, simply because bag doesn't exist anymore when your view is rendered.

What is happening, the Unity UI Builder reads from the UXML file your XML architecture and, then, import it into a VisualTreeAsset which is ready for runtime (without bag).

The only way to get the "bag" is to deserialize the XML yourself by referencing the UXML file and go through each markup to find yours and get attributes you want.

 

DarkRewar, bag is certainly accessable during runtime as I displayed in the code in the first post (inside Init method).
So it certainly possible to implement a new bag property which will hold that value.

 

Still believe that it's a good suggestion, so bumping thread to have some input from Unity team

 

Got it thanks for the detailed answer!