Inject behavior for the existing UI Toolkit VisualElements available in the scene

[mdm88]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

• Extenject does no inject UI Toolkits VisualElement clases

What is the new behavior?

• Extenject now does inject every UI Toolkits VisualElement added to the scene. It supports multiple UIDocuments.

Does this introduce a breaking change?

• Yes
• No

Other information

On which Unity version has this been tested?

• 2021.2
• 2020.4 LTS
• 2020.3
• 2020.2
• 2020.1
• 2019.4 LTS
• 2019.3
• 2019.2
• 2019.1
• 2018.4 LTS

Scripting backend:

• Mono
• IL2CPP

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[doctorseus]

I guess this is required when VisualElements are created by UI Toolkit itself when they are part of a uxml file definition?

The pull request description is a bit broad as I could also just create VisualElements at runtime using existing Extenject mechanism to support inject fields.

One thing to note is also that when you have the situation that you load a uxml file at runtime using Resources.Load<VisualTreeAsset>("...").CloneTree() it would then not have any injected fields I guess VS this situation here where it is already loaded on Scene start so they are available for injection.

[mdm88]

You are right, when creating VisualElements at runtime im using a simple factory. But this adds support for elements already added to the scene.

One thing to note is also that when you have the situation that you load a uxml file at runtime using Resources.Load("...").CloneTree() it would then not have any injected fields I guess VS this situation here where it is already loaded on Scene start so they are available for injection.

Its true, i didnt thought about that

[Mathijs-Bakker]

You are right, when creating VisualElements at runtime im using a simple factory. But this adds support for elements already added to the scene.

One thing to note is also that when you have the situation that you load a uxml file at runtime using Resources.Load("...").CloneTree() it would then not have any injected fields I guess VS this situation here where it is already loaded on Scene start so they are available for injection.

Its true, i didnt thought about that

I don't have any experience with the 'new' UI toolkit. As I still encounter the 'the good old' UnityUI system.
I can see te use of this PR. So I am going to merge this into master.

For a Loading UXML/VisualTreeAsset injecting behavior will be something to dive into next.

[Mathijs-Bakker]

good