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Feature Request Make UxmlElement attribute of a derived class optional

Discussion in 'UI Toolkit' started by Hellfim, Sep 28, 2023.

  1. Hellfim

    Hellfim

    Joined:
    Sep 11, 2014
    Posts:
    91
    Suppose I have following classes:
    Code (CSharp):
    1. [UxmlElement]
    2. public partial class BaseClass : VisualElement
    3. {
    4. }
    5.  
    6. [UxmlElement]
    7. public partial class DerivedClass : BaseClass
    8. {
    9. }
    Now it's possible to omit UxmlElement on a derived class, though UI Toolkit will not be able to work with DerivedClass and will display 'Unknown class: <full class name>' error instead of the VisualElement.

    I would love if you make it possible to use following declaration:
    Code (CSharp):
    1. public class DerivedClass : BaseClass
    2. {
    3. }
     
    Hellfim, Sep 28, 2023
    #1

  2. karl_jones

    karl_jones

    Unity Technologies

    Joined:
    May 5, 2015
    Posts:
    7,820
    We need the attribute for element creation, it takes the place of the UxmlFactory. Is there a reason you don't want to add it?
     
    karl_jones, Sep 28, 2023
    #2

  3. Hellfim

    Hellfim

    Joined:
    Sep 11, 2014
    Posts:
    91
    Well, if there is no uxml-related code in DerivedClass (i.e. no UxmlAttributes), then it seems that it's possible to use a base factory to create class.

    Actually the only reason I brought up, is because I have a generic BaseClass which handles all uxml-related stuff, and it's DerivedClasses are only directly specifing generic parameter, and slightly customize their behaviour.
     
    Hellfim, Sep 28, 2023
    #3

  4. karl_jones

    karl_jones

    Unity Technologies

    Joined:
    May 5, 2015
    Posts:
    7,820
    We cant use the base factory because its responsible for creating the instance and needs the actual type. It generates this method
    https://docs.unity3d.com/2023.3/Doc...ements.UxmlSerializedData.CreateInstance.html

    Which just creates a new instance of the type.
    E.G

    Code (csharp):
    1. public partial class DerivedClass : BaseClass
    2. {
    3.     public class UxmlSerializedData : BaseClass.UxmlSerializedData
    4.     {
    5.         public override object CreateInstance() => new DerivedClass();
    6.     }
    7. }
    So you do need to have the generated code if you want the element to be serialized from uxml.
    The BaseClass will just create a new BaseClass, it would not work with a derived type.
     
    karl_jones, Sep 28, 2023
    #4
    Hellfim likes this.