{"record":{"id":"f4ae3217109612b5","repo":"PrismLibrary/Prism","slug":"an-exception-occurred-while-creating-a-region-with-name-0","errorCode":null,"errorMessage":"An exception occurred while creating a region with name '{0}'. The exception was: {1}.","messagePattern":"An exception occurred while creating a region with name '(.+?)'\\. The exception was: (.+?)\\.","errorType":"exception","errorClass":"RegionCreationException","httpStatus":null,"severity":"error","filePath":"src/Maui/Prism.Maui/Navigation/Regions/Behaviors/DelayedRegionCreationBehavior.cs","lineNumber":140,"sourceCode":"        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        }\n    }\n\n    /// <summary>\n    /// Add the instance of this class to <see cref=\"_instanceTracker\"/> to keep it alive\n    /// </summary>\n    private void Track()\n    {\n        lock (_trackerLock)\n        {\n            if (!_instanceTracker.Contains(this))\n            {\n                _instanceTracker.Add(this);\n            }\n        }\n    }\n\n    /// <summary>","sourceCodeStart":122,"sourceCodeEnd":158,"githubUrl":"https://github.com/PrismLibrary/Prism/blob/358118cd640d9a22ff8cf21c8ad197fa038b7990/src/Maui/Prism.Maui/Navigation/Regions/Behaviors/DelayedRegionCreationBehavior.cs#L122-L158","documentation":"CreateRegion wraps any failure while initializing a region (adapter lookup, adapter.Initialize, container resolution) in a RegionCreationException whose message names the region and the inner exception. It tells you region construction itself failed, with the original cause as InnerException.","triggerScenarios":"regionAdapterMappings.GetMapping throws for an unregistered element type, or regionAdapter.Initialize fails (e.g. container not yet available, invalid regionName, adapter threw), all inside CreateRegion's try block.","commonSituations":"Forgot to register an IRegionAdapter for a custom control type; container misconfiguration after App.RegisterServices changes; region name collisions; Maui version upgrades changing VisualElement behavior.","solutions":["Read the InnerException to find the real cause","Register a region adapter mapping for the host element type in your PrismAppBuilder configuration (ConfigureRegionAdapterMappings)","Verify the DI container is configured before any region creation","Check for duplicate region names or invalid adapter initialization logic"],"exampleFix":"// before\n// no adapter for custom host -> RegionCreationException\n// after\nprotected override void ConfigureRegionAdapterMappings(IRegionAdapterMappings regionAdapterMappings)\n{\n    base.ConfigureRegionAdapterMappings(regionAdapterMappings);\n    regionAdapterMappings.RegisterMapping(typeof(MyCustomHost), Container.Resolve<MyHostRegionAdapter>());\n}","handlingStrategy":"try-catch","validationCode":"if (_regionAdapterMappings.GetMapping(host.GetType()) is null) throw new InvalidOperationException($\"No region adapter for {host.GetType().Name}\");","typeGuard":null,"tryCatchPattern":"try { /* region activation */ }\ncatch (RegionCreationException ex)\n{ logger.Error(ex.InnerException, \"Region '{Region}' failed\", ex.RegionName); }","preventionTips":["Register adapters for all custom host types via ConfigureRegionAdapterMappings","Initialize DI container before any region usage","Keep region names unique and valid","Catch RegionCreationException and surface InnerException in diagnostics"],"tags":["maui","regions","region-adapter","wrapped-exception"],"backgroundTag":"api-error-response","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"}