PrismLibrary/Prism · error · InvalidOperationException

Resources.ContentControlHasContentException

Error message

Resources.ContentControlHasContentException

What it means

ContentControlRegionAdapter.Adapt requires the target ContentControl's Content to be unset: if Content is non-null or has a binding on ContentControl.ContentProperty, it throws InvalidOperationException with Resources.ContentControlHasContentException. The region adapter must own the Content property to swap in the active view.

Solutions

  1. Clear the Content property/binding on the ContentControl and let the region manage content.
  2. Use a separate empty ContentControl as the region host and keep your bound control as a view inside the region.
  3. Move the previously-set content into a view registered with the region.
  4. Check for XAML child elements implicitly setting Content.

Example fix

// before
<ContentControl Content="{Binding Detail}" prism:RegionManager.RegionName="DetailRegion" />
// after
<ContentControl prism:RegionManager.RegionName="DetailRegion" />
Defensive patterns

Strategy: validation

Validate before calling

if (contentControl.Content != null || contentControl.HasBinding(ContentControl.ContentProperty))
    throw new InvalidOperationException("ContentControl region host must have no Content set.");

Type guard

bool IsRegionCompatible(ContentControl c) => c.Content == null && !c.HasBinding(ContentControl.ContentProperty);

Try / catch

try
{
    RegionManager.SetRegionName(contentControl, "DetailRegion");
}
catch (InvalidOperationException ex) when (ex.Message.Contains("Content"))
{
    logger.LogError(ex, "ContentControl already has Content; cannot be a region host.");
}

Prevention

When it happens

Trigger: Setting RegionManager.RegionName on a ContentControl whose Content is already set in XAML (e.g., <ContentControl Content="{Binding ...}" RegionName="..."/>) or assigned in code before region attachment.

Common situations: Adding RegionName to an existing content-bound control during MVVM refactors; implicit content from XAML child elements (the child becomes Content); design-time data left in the control at runtime.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/c73b503a41a8cb20. Report an issue: GitHub.

Appendix: source

Thrown at src/Wpf/Prism.Wpf/Navigation/Regions/ContentControlRegionAdapter.cs:39

        /// <summary>
        /// Adapts a <see cref="ContentControl"/> to an <see cref="IRegion"/>.
        /// </summary>
        /// <param name="region">The new region being used.</param>
        /// <param name="regionTarget">The object to adapt.</param>
        protected override void Adapt(IRegion region, ContentControl regionTarget)
        {
            if (regionTarget == null)
                throw new ArgumentNullException(nameof(regionTarget));

            bool contentIsSet = regionTarget.Content != null;
#if !AVALONIA
            contentIsSet = contentIsSet || regionTarget.HasBinding(ContentControl.ContentProperty);
#else
            contentIsSet = contentIsSet || regionTarget[ContentControl.ContentProperty] != null;
#endif

            if (contentIsSet)
                throw new InvalidOperationException(Resources.ContentControlHasContentException);

            region.ActiveViews.CollectionChanged += delegate
            {
                regionTarget.Content = region.ActiveViews.FirstOrDefault();
            };

            region.Views.CollectionChanged +=
                (sender, e) =>
                {
                    if (e.Action == NotifyCollectionChangedAction.Add && region.ActiveViews.Count() == 0)
                    {
                        region.Activate(e.NewItems[0]);
                    }
                };
        }

        /// <summary>
        /// Creates a new instance of <see cref="SingleActiveRegion"/>.

View on GitHub (pinned to 358118cd64)