stride3d/stride · error · ArgumentNullException

ArgumentNullException: session

Error message

ArgumentNullException: session

What it means

The NewProjectTemplateCollectionViewModel constructor requires a SessionViewModel representing the editor session; it throws ArgumentNullException when session is null because the template collection is built from the session's template descriptions.

Solutions

1. Ensure the SessionViewModel is fully initialized before constructing this view model
2. Null-check/guard the session source (service locator or parent view model)
3. Fix initialization order so the session is created before template-dependent UI

Example fix

// before
var vm = new NewProjectTemplateCollectionViewModel(serviceProvider, session); // session may be null
// after
if (session == null) throw new InvalidOperationException("Session must be initialized before showing project templates");
var vm = new NewProjectTemplateCollectionViewModel(serviceProvider, session);

if (session == null) throw new InvalidOperationException("Editor session must be loaded before listing project templates");

bool SessionReady(SessionViewModel s) => s != null && s.IsInitialized;

try { var vm = new NewProjectTemplateCollectionViewModel(sp, session); } catch (ArgumentNullException ex) when (ex.ParamName == "session") { /* abort dialog open; report session not ready */ }

When it happens

Trigger: Constructing NewProjectTemplateCollectionViewModel with a null session — e.g. the SessionViewModel has not been created yet, or a service locator returned null before session initialization.

Common situations: Opening the new-project dialog before the editor session loads; DI ordering issues where the view model is built before the session; failed session load silently yielding null.

Related errors

• ArgumentNullException: templates
• ArgumentNullException: removeAction
• Value cannot be null. (Parameter 'values')
• entity must contain a non-null asset entity.
• ArgumentNullException: dependencyManager

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/1a21539848cdf8e4. Report an issue: GitHub.

Appendix: source

Thrown at sources/editor/Stride.Core.Assets.Editor/Components/TemplateDescriptions/ViewModels/NewProjectTemplateCollectionViewModel.cs:23

using System.Linq;
using Stride.Core.Assets.Editor.Settings;
using Stride.Core.Assets.Editor.ViewModel;
using Stride.Core.Assets.Templates;
using Stride.Core.Extensions;
using Stride.Core.IO;
using Stride.Core.Presentation.ViewModels;

namespace Stride.Core.Assets.Editor.Components.TemplateDescriptions.ViewModels
{
    public class NewProjectTemplateCollectionViewModel : ProjectTemplateCollectionViewModel
    {
        private readonly TemplateDescriptionGroupViewModel rootGroup;
        private bool arePropertiesValid;

        public NewProjectTemplateCollectionViewModel(IViewModelServiceProvider serviceProvider, SessionViewModel session)
            : base(serviceProvider)
        {
            if (session == null) throw new ArgumentNullException(nameof(session));
            Session = session;

            rootGroup = new TemplateDescriptionGroupViewModel(serviceProvider, "All templates");

            // Add a default General group
            var defaultGroup = new TemplateDescriptionGroupViewModel(rootGroup, "General");
            
            foreach (TemplateDescription template in session.FindTemplates(TemplateScope.Session))
            {
                if (!IsAssetsOnlyTemplate(template))
                    continue;

                var viewModel = new PackageTemplateViewModel(serviceProvider, template, session);
                var group = ProcessGroup(rootGroup, template.Group) ?? defaultGroup;
                group.Templates.Add(viewModel);
            }

            Location = session.SolutionPath.GetFullDirectory() ?? InternalSettings.TemplatesWindowDialogLastNewSessionTemplateDirectory.GetValue();

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