stride3d/stride · error · InvalidOperationException

The OnComboBoxClosedWithSelectionBehavior must be attached…

Error message

The OnComboBoxClosedWithSelectionBehavior must be attached to a ComboBox.

What it means

OnComboBoxClosedWithSelectionBehavior checks in OnAttached that the AssociatedObject is a ComboBox because its OnEvent handler relies on the ComboBox DropDownClosed event and its SelectedItem semantics. Attaching it to any other element throws InvalidOperationException immediately.

Solutions

Move the behavior declaration onto a ComboBox element in XAML
If the target is not a ComboBox, use the appropriate behavior for that control type
For programmatic attachment, check 'if (target is ComboBox)' before adding the behavior

Example fix

// before
<TextBox>
  <i:Interaction.Behaviors>
    <b:OnComboBoxClosedWithSelectionBehavior/>
  </i:Interaction.Behaviors>
</TextBox>
// after
<ComboBox>
  <i:Interaction.Behaviors>
    <b:OnComboBoxClosedWithSelectionBehavior/>
  </i:Interaction.Behaviors>
</ComboBox>

Defensive patterns

Strategy: type-guard

Validate before calling

if (element is ComboBox) element.AddBehavior(new OnComboBoxClosedWithSelectionBehavior());

Type guard

static bool CanAttachComboBoxClosedBehavior(object o) => o is ComboBox;

Try / catch

try { behaviors.Add(new OnComboBoxClosedWithSelectionBehavior()); }
catch (InvalidOperationException ex) { log.Warn($"Wrong AssociatedObject: {ex.Message}"); }

Prevention

Verify the behavior's documented target control before reuse
Keep behavior XAML co-located with its target control type
Use code-behind attachment with a type check when unsure

When it happens

Trigger: Attaching the behavior (via Interaction.Behaviors in XAML or code) to anything other than a ComboBox, e.g. a TextBox, DataGrid, or plain Control.

Common situations: Copy-paste of behavior markup between controls; refactor renaming a ComboBox to another control while leaving the behavior attached; generic event-trigger behaviors reused on the wrong element.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/ce3b5c8887eb69da. Report an issue: GitHub.

Appendix: source

Thrown at sources/editor/Stride.Core.Assets.Editor/View/Behaviors/OnComboBoxClosedWithSelectionBehavior.cs:20

// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.
using System;
using System.Windows.Controls;

using Stride.Core.Presentation.Behaviors;

namespace Stride.Core.Assets.Editor.View.Behaviors
{
    public class OnComboBoxClosedWithSelectionBehavior : OnEventCommandBehavior
    {
        public OnComboBoxClosedWithSelectionBehavior()
        {
            EventName = "DropDownClosed";
        }

        protected override void OnAttached()
        {
            if (!(AssociatedObject is ComboBox))
                throw new InvalidOperationException("The OnComboBoxClosedWithSelectionBehavior must be attached to a ComboBox.");

            base.OnAttached();
        }

        protected override void OnEvent()
        {
            var comboBox = (ComboBox)AssociatedObject;
            if (comboBox.SelectedItem != null)
                base.OnEvent();
        }
    }
}

View on GitHub (pinned to 96fad776d2)