dotnet/maui · error · InvalidOperationException

call Forms.Init() before this

Error message

call Forms.Init() before this

What it means

PageExtensions.CreateContainer (GTK) builds the hosting container for a Page. It requires the Forms compatibility runtime to be initialized (Forms.IsInitialized) and throws InvalidOperationException('call Forms.Init() before this') otherwise, because the platform/handlers it constructs depend on initialized Forms state.

Source

Thrown at src/Compatibility/Core/src/GTK/Extensions/PageExtensions.cs:10

using System;

namespace Microsoft.Maui.Controls.Compatibility.Platform.GTK.Extensions
{
	public static class PageExtensions
	{
		public static GtkFormsContainer CreateContainer(this Page view)
		{
			if (!Forms.IsInitialized)
				throw new InvalidOperationException("call Forms.Init() before this");

			if (!(view.RealParent is Application))
			{
				Application app = new DefaultApplication();
				app.MainPage = view;
			}

			var result = new Platform();
			result.SetPage(view);

			return result.PlatformRenderer;
		}

		class DefaultApplication : Application
		{
		}
	}
}

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Call Forms.Init() (GTK overload) early in the GTK app entry, before creating/showing any Page or container.
2. Ensure the Init call precedes any CreateContainer/Platform.SetPage usage.
3. If embedding, init Forms at application startup rather than on first use.

Example fix

// before
var window = myPage.CreateContainer(); // throws — Forms not initialized
// after
Gtk.Application.Init();
Forms.Init(); // GTK init
var window = myPage.CreateContainer();

static GtkFormsContainer SafeCreateContainer(Page p)
{
    if (!Forms.IsInitialized)
        throw new InvalidOperationException("Call Forms.Init() before CreateContainer.");
    return p.CreateContainer();
}

static bool FormsReady => Forms.IsInitialized;

When it happens

Trigger: Calling page.CreateContainer() (or the GTK hosting entry that uses it) before Forms.Init(...) has run. Typical of an app whose Main/entry method tries to show a Page before bootstrapping Forms.

Common situations: GTK app entry point invoking CreateContainer on a Page before calling Forms.Init(); reordered startup code; a test or design-time host that bypasses Forms.Init; migration from a template that inits Forms lazily.

Related errors

• call GtkThemes.Init() before this
• Unable to find Application Services
• Unable to find Application Services
• MinimumDate must be lower than MaximumDate
• MaximumDate must be greater than MinimumDate

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/3de26d630bfed44c. Report an issue: GitHub.