{"record":{"id":"410c937ddf16ad8d","repo":"PrismLibrary/Prism","slug":"navigation-cannot-proceed-until-a-region-is-set-for-the","errorCode":null,"errorMessage":"Navigation cannot proceed until a region is set for the RegionNavigationService.","messagePattern":"Navigation cannot proceed until a region is set for the RegionNavigationService\\.","errorType":"exception","errorClass":"InvalidOperationException","httpStatus":null,"severity":"error","filePath":"src/Maui/Prism.Maui/Navigation/Regions/Navigation/RegionNavigationService.cs","lineNumber":109,"sourceCode":"            throw new ArgumentNullException(nameof(navigationCallback));\n\n        try\n        {\n            DoNavigate(target, navigationCallback, regionParameters);\n        }\n        catch (Exception e)\n        {\n            NotifyNavigationFailed(new NavigationContext(this, target), navigationCallback, e);\n        }\n    }\n\n    private void DoNavigate(Uri source, Action<NavigationResult> navigationCallback, INavigationParameters regionParameters)\n    {\n        if (source == null)\n            throw new ArgumentNullException(nameof(source));\n\n        if (Region == null)\n            throw new InvalidOperationException(Resources.NavigationServiceHasNoRegion);\n\n        _currentNavigationContext = new NavigationContext(this, source, regionParameters);\n\n        // starts querying the active views\n        RequestCanNavigateFromOnCurrentlyActiveView(\n            _currentNavigationContext,\n            navigationCallback,\n            Region.ActiveViews.OfType<VisualElement>().ToArray(),\n            0);\n    }\n\n    private void RequestCanNavigateFromOnCurrentlyActiveView(\n        NavigationContext navigationContext,\n        Action<NavigationResult> navigationCallback,\n        VisualElement[] activeViews,\n        int currentViewIndex)\n    {\n        if (currentViewIndex < activeViews.Length)","sourceCodeStart":91,"sourceCodeEnd":127,"githubUrl":"https://github.com/PrismLibrary/Prism/blob/358118cd640d9a22ff8cf21c8ad197fa038b7990/src/Maui/Prism.Maui/Navigation/Regions/Navigation/RegionNavigationService.cs#L91-L127","documentation":"DoNavigate throws InvalidOperationException when the Region property has not been assigned. A RegionNavigationService is only usable once it is attached to a region (via IRegion.NavigationService); navigation cannot proceed without an owning region. This is a lifecycle/state error, not an argument error.","triggerScenarios":"Calling RequestNavigate on a region navigation service that was created but never assigned to a region — e.g. resolving IRegionNavigationService from the container directly and navigating without setting Region.","commonSituations":"Manually resolving RegionNavigationService instead of getting it from region.NavigationService; region not yet attached during early app startup; custom region adapters that forget to attach the navigation service via region behaviors.","solutions":["Always navigate through region.NavigationService obtained from an attached region (regionManager.Regions[\"Name\"].NavigationService.RequestNavigate(...)).","Ensure the region exists before navigating: check regionManager.Regions.ContainsRegionName(\"...\").","Make sure your custom IRegionAdapter registers the navigation behaviors so Region gets set before navigation."],"exampleFix":"// before\nvar navService = container.Resolve<IRegionNavigationService>();\nnavService.RequestNavigate(new Uri(\"MainView\", UriKind.Relative), r => { });\n// after\nvar region = regionManager.Regions[\"ContentRegion\"];\nregion.NavigationService.RequestNavigate(new Uri(\"MainView\", UriKind.Relative), r => { });","handlingStrategy":"validation","validationCode":"if (!regionManager.Regions.ContainsRegionName(\"ContentRegion\"))\n    throw new InvalidOperationException(\"Region not registered yet\");\nregionManager.Regions[\"ContentRegion\"].NavigationService.RequestNavigate(uri, r => { });","typeGuard":"bool CanNavigate(IRegion region) => region is not null && region.NavigationService?.Region is not null;","tryCatchPattern":"try\n{\n    region.NavigationService.RequestNavigate(uri, result => OnNavigated(result));\n}\ncatch (InvalidOperationException)\n{\n    // region not attached yet; defer navigation until region is available\n}","preventionTips":["Navigate only through region.NavigationService from regionManager.Regions[...].","Wait for the view hosting the region to load before navigating (e.g. OnLoaded).","Ensure custom region adapters attach the navigation behaviors that set Region."],"tags":["invalid-state","navigation","lifecycle","prism"],"backgroundTag":"invalid-state-transition","analyzedSha":"358118cd640d9a22ff8cf21c8ad197fa038b7990","analyzedAt":"2026-09-15T15:00:31.079Z","contentChangedAt":"2026-09-15T15:00:31.079Z","schemaVersion":2},"datasetVersion":"2026-09-16T04:17:20.429Z"}