stride3d/stride · error · InvalidOperationException

The associated slider must have a Track child named…

Error message

The associated slider must have a Track child named 'PART_Track'

What it means

SliderDragFromTrackBehavior lets users start dragging the slider thumb by clicking anywhere on the slider's track. In SliderInitialized it applies the template and looks for a Track visual child; if none is found or the found track is not named 'PART_Track', it throws InvalidOperationException because dragging cannot be wired up without the standard slider Track part.

Solutions

Restore a <Track x:Name="PART_Track"/> element in the slider's ControlTemplate (standard Slider templates always include it).
Ensure the Track's name is exactly PART_Track — the check is case-sensitive and name-based.
Verify the behavior is attached to a Slider that actually loads that template (correct Template/Style applied, not a fallback).
If the template can't change, remove the behavior or implement track-click handling without this behavior.

Example fix

<!-- before: custom template without a Track part -->
<ControlTemplate TargetType="Slider">
  <Border Background="{TemplateBinding Background}" />
</ControlTemplate>

<!-- after -->
<ControlTemplate TargetType="Slider">
  <Track x:Name="PART_Track" Value="{TemplateBinding Value}">
    <Track.Thumb>
      <Thumb />
    </Track.Thumb>
  </Track>
</ControlTemplate>

Defensive patterns

Strategy: validation

Validate before calling

slider.ApplyTemplate();
var track = slider.FindVisualChildOfType<Track>();
if (track == null || track.Name != "PART_Track")
    log.Warn("Slider template lacks PART_Track; SliderDragFromTrackBehavior will throw.");

Type guard

static bool HasSliderTrackPart(Slider s) { s.ApplyTemplate(); var t = s.FindVisualChildOfType<Track>(); return t?.Name == "PART_Track"; }

Try / catch

try { behavior.Attach(slider); }
catch (InvalidOperationException ex) when (ex.Message.Contains("PART_Track")) { log.Error("Slider template must include <Track x:Name='PART_Track'/>"); }

Prevention

Base custom slider styles on the default Slider template so PART_Track is preserved.
Never rename or remove the PART_Track part in a custom template.
Smoke-test custom-styled sliders with this behavior attached before shipping themes.

When it happens

Trigger: Attaching the behavior to a custom slider whose ControlTemplate does not include a Track named PART_Track, or whose template hasn't produced a Track visual child after ApplyTemplate; attaching before/during template application such that FindVisualChildOfType<Track> runs too early in some custom templates.

Common situations: Using a custom or third-party slider style that renamed or removed PART_Track; building a minimal slider template for a lightweight look without a Track; attaching the behavior to a control that isn't actually a slider template host.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/52b74bae45339ecd. Report an issue: GitHub.

Appendix: source

Thrown at sources/presentation/Stride.Core.Presentation.Wpf/Behaviors/SliderDragFromTrackBehavior.cs:46

        protected override void OnDetaching()
        {
            AssociatedObject.Initialized -= SliderInitialized;
            AssociatedObject.RemoveHandler(UIElement.PreviewMouseLeftButtonDownEvent, (MouseButtonEventHandler)TrackMouseEvent);
            AssociatedObject.RemoveHandler(UIElement.PreviewMouseLeftButtonUpEvent, (MouseButtonEventHandler)TrackMouseEvent);
            if (track != null && track.Thumb != null)
            {
                track.Thumb.MouseEnter -= MouseEnter;
            }
            base.OnDetaching();
        }

        private void SliderInitialized(object sender, EventArgs e)
        {
            AssociatedObject.ApplyTemplate();

            track = AssociatedObject.FindVisualChildOfType<Track>();
            if (track == null || track.Name != "PART_Track")
                throw new InvalidOperationException("The associated slider must have a Track child named 'PART_Track'");
            track.Thumb.MouseEnter += MouseEnter;
            AssociatedObject.Initialized += SliderInitialized;
        }

        private void TrackMouseEvent(object sender, [NotNull] MouseButtonEventArgs e)
        {
            if (e.ChangedButton == MouseButton.Left)
                trackMouseDown = e.ButtonState == MouseButtonState.Pressed;
        }

        private void MouseEnter(object sender, [NotNull] MouseEventArgs e)
        {
            if (trackMouseDown)
            {
                var args = new MouseButtonEventArgs(e.MouseDevice, e.Timestamp, MouseButton.Left) { RoutedEvent = UIElement.MouseLeftButtonDownEvent };
                track.Thumb.RaiseEvent(args);
                trackMouseDown = false;
            }

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