{"record":{"id":"24a63060226ed569","repo":"PrismLibrary/Prism","slug":"resources-viewnotinregionexception","errorCode":null,"errorMessage":"Resources.ViewNotInRegionException","messagePattern":"Resources\\.ViewNotInRegionException","errorType":"exception","errorClass":"ArgumentException","httpStatus":null,"severity":"error","filePath":"src/Wpf/Prism.Wpf/Navigation/Regions/Region.cs","lineNumber":433,"sourceCode":"#else\n            if (view is AvaloniaObject avaloniaObject)\n            {\n                Regions.RegionManager.SetRegionManager(avaloniaObject, scopedRegionManager);\n            }\n#endif\n\n            ItemMetadataCollection.Add(itemMetadata);\n        }\n\n        private ItemMetadata GetItemMetadataOrThrow(object view)\n        {\n            if (view == null)\n                throw new ArgumentNullException(nameof(view));\n\n            ItemMetadata itemMetadata = ItemMetadataCollection.FirstOrDefault(x => x.Item == view);\n\n            if (itemMetadata == null)\n                throw new ArgumentException(Resources.ViewNotInRegionException, nameof(view));\n\n            return itemMetadata;\n        }\n\n        private void OnPropertyChanged(string propertyName)\n        {\n            PropertyChanged?.Invoke(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));\n        }\n\n        /// <summary>\n        /// The default sort algorithm.\n        /// </summary>\n        /// <param name=\"x\">The first view to compare.</param>\n        /// <param name=\"y\">The second view to compare.</param>\n        /// <returns></returns>\n        [SuppressMessage(\"Microsoft.Naming\", \"CA1704:IdentifiersShouldBeSpelledCorrectly\", MessageId = \"y\")]\n        [SuppressMessage(\"Microsoft.Naming\", \"CA1704:IdentifiersShouldBeSpelledCorrectly\", MessageId = \"x\")]\n        public static int DefaultSortComparison(object x, object y)","sourceCodeStart":415,"sourceCodeEnd":451,"githubUrl":"https://github.com/PrismLibrary/Prism/blob/358118cd640d9a22ff8cf21c8ad197fa038b7990/src/Wpf/Prism.Wpf/Navigation/Regions/Region.cs#L415-L451","documentation":"Region.GetItemMetadataOrThrow throws ArgumentException with ViewNotInRegionException for parameter \"view\" when the supplied view instance is not found in the region's ItemMetadataCollection. Methods like Activate, Deactivate, and Remove delegate to this helper, so operating on a view the region doesn't contain fails here.","triggerScenarios":"Calling region.Remove(view), region.Activate(view), or region.Deactivate(view) with a view instance that was never added to this region (or was already removed), or with a different instance of the same view type.","commonSituations":"Cross-region confusion — activating a view in region A that lives in region B; using a new'd-up view instance instead of the registered one; stale references kept after Remove.","solutions":["Add the view to the region before activating/deactivating/removing it.","Confirm you are using the exact registered instance (e.g. retrieved from region.Views or region.GetView(name)), not a new instance.","Guard with region.Views.Contains(view) before calling the operation."],"exampleFix":"// before\nregion.Activate(myView); // may not belong to this region\n// after\nif (region.Views.Contains(myView))\n    region.Activate(myView);","handlingStrategy":"validation","validationCode":"if (view == null || !region.Views.Contains(view))\n    return; // view not managed by this region\nregion.Activate(view);","typeGuard":null,"tryCatchPattern":"try\n{\n    region.Remove(view);\n}\ncatch (ArgumentException)\n{\n    // view was not in this region — nothing to remove\n}","preventionTips":["Keep track of which region each view belongs to (view's RegionManager).","Only pass instances obtained from region.Views or region.GetView(name).","Guard Activate/Deactivate/Remove with region.Views.Contains(view)."],"tags":["wpf","prism","region","argument","not-found"],"backgroundTag":"resource-not-found","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"}