{"record":{"id":"78d74eeb051b14dc","repo":"PrismLibrary/Prism","slug":"argumentnullexception-for-target","errorCode":null,"errorMessage":"ArgumentNullException for 'target'","messagePattern":"ArgumentNullException for 'target'","errorType":"exception","errorClass":"ArgumentNullException","httpStatus":null,"severity":"error","filePath":"src/Maui/Prism.Maui/Navigation/Regions/Xaml/RegionManager.cs","lineNumber":155,"sourceCode":"        CreateRegion(view);\n    }\n\n    private static void CreateRegion(VisualElement element)\n    {\n        var regionCreationBehavior = ContainerLocator.Container.Resolve<DelayedRegionCreationBehavior>();\n        regionCreationBehavior.TargetElement = element;\n        regionCreationBehavior.Attach();\n    }\n\n    /// <summary>\n    /// Gets the value of the <see cref=\"RegionNameProperty\"/> attached property.\n    /// </summary>\n    /// <param name=\"target\">The target element.</param>\n    /// <returns>The <see cref=\"IRegionManager\"/> attached to the <paramref name=\"target\"/> element.</returns>\n    public static IRegionManager GetRegionManager(VisualElement target)\n    {\n        if (target == null)\n            throw new ArgumentNullException(nameof(target));\n\n        return (IRegionManager)target.GetValue(RegionManagerProperty);\n    }\n\n    /// <summary>\n    /// Sets the <see cref=\"RegionManagerProperty\"/> attached property.\n    /// </summary>\n    /// <param name=\"target\">The target element.</param>\n    /// <param name=\"value\">The value.</param>\n    public static void SetRegionManager(VisualElement target, IRegionManager value)\n    {\n        if (target == null)\n            throw new ArgumentNullException(nameof(target));\n\n        target.SetValue(RegionManagerProperty, value);\n    }\n\n    private static void OnRegionContextChanged(BindableObject bindable, object oldValue, object newValue)","sourceCodeStart":137,"sourceCodeEnd":173,"githubUrl":"https://github.com/PrismLibrary/Prism/blob/358118cd640d9a22ff8cf21c8ad197fa038b7990/src/Maui/Prism.Maui/Navigation/Regions/Xaml/RegionManager.cs#L137-L173","documentation":"RegionManager.GetRegionManager retrieves the IRegionManager attached to a VisualElement via the RegionManager attached property. It throws ArgumentNullException when the target element is null, as no attached value can be read.","triggerScenarios":"Calling RegionManager.GetRegionManager(null).","commonSituations":"Resolving a scoped region manager from a page whose content is null; passing a ViewModel or service instead of a VisualElement.","solutions":["Pass the actual VisualElement (e.g. the page or its content region host).","Null-check the element before retrieving the region manager.","If a null region manager result is also possible, cast-check or null-check the returned value."],"exampleFix":"// before\nvar rm = RegionManager.GetRegionManager(null);\n// after\nvar rm = element is not null ? RegionManager.GetRegionManager(element) : null;","handlingStrategy":"type-guard","validationCode":"if (target is null) return null;","typeGuard":"var rm = target is VisualElement el ? RegionManager.GetRegionManager(el) : null;","tryCatchPattern":"try { rm = RegionManager.GetRegionManager(element); }\ncatch (ArgumentNullException) { rm = null; }","preventionTips":["Null-check the resolved element before fetching its region manager.","Also null-check the returned IRegionManager for elements without a scope."],"tags":["prism","maui","regions","argument-null","region-manager"],"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"}