EditText UI element IsSelectionActive throws object reference error

[BlackCurtainStudio]

Release Type: Official Release

Version: 4.2.0.2282

Platform(s): Windows

Describe the bug
When enabling and focusing a EditText UI element using IsSelectionActive = true, the error Object reference not set to an instance of an object is thrown. However, the EditText element seems to be responsive and accepts input anyway.

To Reproduce
Repro project: https://github.com/BlackCurtainStudio/Stride-EditTextSample

Expected behavior
No errors should occur.

Screenshots

Log and callstacks
[EditTextSample.UiScript]: Error: Object reference not set to an instance of an object. [EditTextSample.UiScript]: Error: at Stride.Core.ServiceRegistryExtensions.GetSafeServiceAs[T](IServiceRegistry registry) in C:\BuildAgent\work\b5f46e3c4829a09e\sources\core\Stride.Core\ServiceRegistryExtensions.cs:line 22 at Stride.UI.Controls.EditText.ActivateEditTextImpl() in C:\BuildAgent\work\b5f46e3c4829a09e\sources\engine\Stride.UI\Controls\EditText.Direct.cs:line 125 at Stride.UI.Controls.EditText.set_IsSelectionActive(Boolean value) in C:\BuildAgent\work\b5f46e3c4829a09e\sources\engine\Stride.UI\Controls\EditText.cs:line 160

[TranquilAbyss]

Providing some research I did for whom ever picks this up.

Problem
I think this exception is happening when UIComponent is enabled and IsSelectionActive = true happens in the same frame.

Work Around

• Wait another frame before running UIComponent IsSelectionActive = true
• Enable UIComponent from the start and avoid the problem entirely.

Problem Explanation
This happens due to the EditText not having a Services set until the update run. This seems to be a unique problem to EditText.Direct (not that I tested it) due to UIElementServices.Services.GetSafeServiceAs<InputManager>(); being in EditText type Direct, but other UIElements may require it too.
The null Services is a IServiceRegistry and they all get set by their parent during run time by the UIElement.Update, where the parent passes their Services (aka registry) to the child. ~This is why running IsSelectionActive = true on the next frame after UIComponent is enabled, works.

protected virtual void Update(GameTime time)
{
    if (Parent != null && !Parent.UIElementServices.Equals(ref uiElementServices))
        uiElementServices = Parent.UIElementServices;
}

I believe the UIRenderFeature DrawInternal that kicks off this process by setting a Page's rootElement which passes down Services to the children through Update.

Edit:
Per jonyfries mention below, Update is only one of two ways to set the Services from the UIElements parent. The UIElementServices getter also sets the services. It makes me wonder if the parent is set at the time of error, otherwise jonyfries is correct and its the root object's Services are not set on the frame the UIComponent is enabled

Two suggestion for solutions

• Try to pass in the Services on the UIElement SetParent, Which may also mean before the UIRenderFeature DrawInternal as well.
• Find a different way for the code to handle ActivateEditTextImpl without needing to accessing Services early. DeactivateEditTextImpl most likely wont need to change, but it could help just in case some tries to call it on the same frame.

This UIElementServices.Services.GetSafeServiceAs<InputManager>(); appears to only be called by EditText Direct from searching the entire solution

[jonyfries]

The same code that is in the Update function is also in the getter for the UIElementServices:

`
internal UIElementServices UIElementServices
{
get
{
if (Parent != null && !Parent.UIElementServices.Equals(ref uiElementServices))
uiElementServices = Parent.UIElementServices;

            return uiElementServices;
        }
        set
        {
            if (Parent != null)
                throw new InvalidOperationException("Can only assign UIElementService to the root element!");

            uiElementServices = value;
        }
    }

`

So it seems to me that the code in the Update function should be unnecessary and that this issue will occur only if the root element doesn't have a UIElementServices defined.