{"record":{"id":"703243452d8ce5ac","repo":"PrismLibrary/Prism","slug":"targetelement","errorCode":null,"errorMessage":"targetElement","messagePattern":"targetElement","errorType":"exception","errorClass":"ArgumentNullException","httpStatus":null,"severity":"error","filePath":"src/Maui/Prism.Maui/Navigation/Regions/Behaviors/DelayedRegionCreationBehavior.cs","lineNumber":123,"sourceCode":"            {\n                string regionName = RegionManagerAccessor.GetRegionName(TargetElement);\n                CreateRegion(TargetElement, regionName);\n                Track();\n                _regionCreated = true;\n            }\n        }\n    }\n\n    /// <summary>\n    /// Method that will create the region, by calling the right <see cref=\"IRegionAdapter\"/>.\n    /// </summary>\n    /// <param name=\"targetElement\">The target element that will host the <see cref=\"IRegion\"/>.</param>\n    /// <param name=\"regionName\">Name of the region.</param>\n    /// <returns>The created <see cref=\"IRegion\"/></returns>\n    protected virtual IRegion CreateRegion(VisualElement targetElement, string regionName)\n    {\n        if (targetElement == null)\n            throw new ArgumentNullException(nameof(targetElement));\n\n        try\n        {\n            if (!targetElement.TryGetParentPage(out var page))\n                throw new Exception(\"The Target Element has not yet been parented and we cannot get the parent page.\");\n\n            // Build the region\n            var container = page.GetContainerProvider();\n            targetElement.SetContainerProvider(container);\n            var regionAdapter = _regionAdapterMappings.GetMapping(targetElement.GetType());\n            var region = regionAdapter.Initialize(targetElement, regionName);\n\n            return region;\n        }\n        catch (Exception ex)\n        {\n            throw new RegionCreationException(string.Format(CultureInfo.CurrentCulture, Resources.RegionCreationException, regionName, ex), ex);\n        }","sourceCodeStart":105,"sourceCodeEnd":141,"githubUrl":"https://github.com/PrismLibrary/Prism/blob/358118cd640d9a22ff8cf21c8ad197fa038b7990/src/Maui/Prism.Maui/Navigation/Regions/Behaviors/DelayedRegionCreationBehavior.cs#L105-L141","documentation":"DelayedRegionCreationBehavior.CreateRegion throws ArgumentNullException when the VisualElement that should host the region (targetElement) is null. This method instantiates the region for a lazily-created host; without a host element there is nothing to adapt.","triggerScenarios":"The delayed creation behavior fires (e.g. on Loaded) but the tracked target element reference is null — the control was garbage-collected, removed from the visual tree, or the WeakReference expired before TryCreateRegion invoked CreateRegion.","commonSituations":"Regions declared inside controls that are unloaded/destroyed quickly; collection virtualization recycling items away; navigation replacing a page before the region behavior's timer/Loaded callback runs.","solutions":["Ensure the element with RegionName stays alive and in the visual tree long enough for region creation","Avoid removing/unloading the host control before its Loaded event fires","Check that the RegionName attached property is set on an actual VisualElement instance, not a template placeholder","Wrap region-hosted content so the host is retained until navigation completes"],"exampleFix":"// before\n<Grid prism:RegionManager.RegionName=\"{Binding MaybeNullRegionName}\" />\n// after\n<Grid IsVisible=\"{Binding HasRegionHost}\"\n      prism:RegionManager.RegionName=\"MyRegion\" />","handlingStrategy":"type-guard","validationCode":"if (targetElement is null || targetElement.Parent is null) return; // skip creation until parented","typeGuard":"bool CanCreateRegion(VisualElement? e) => e is not null && e.TryGetParentPage(out _);","tryCatchPattern":"try { var region = CreateRegion(element, name); }\ncatch (ArgumentNullException ex) { logger.Warn(ex, \"Region host vanished before creation\"); }","preventionTips":["Keep region hosts alive until region creation completes","Avoid RegionName on virtualized/recycled template items","Subscribe to Loaded before triggering region-dependent logic"],"tags":["null-argument","maui","regions","delayed-creation"],"backgroundTag":"null-argument","analyzedSha":"358118cd640d9a22ff8cf21c8ad197fa038b7990","analyzedAt":"2026-09-15T15:00:31.079Z","contentChangedAt":"2026-09-15T15:00:31.079Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}