PrismLibrary/Prism · error · InvalidOperationException

Resources.DeactiveNotPossibleException

Error message

Resources.DeactiveNotPossibleException

What it means

AllActiveRegion keeps every added view active, so it has no notion of deactivation; its Deactivate override unconditionally throws InvalidOperationException with Resources.DeactiveNotPossibleException. This is a deliberate API contract: if you need per-view activation states, use a SingleActiveRegion instead.

Solutions

1. Use a SingleActiveRegion (e.g., RegisterViewWithRegion with a region whose adapter supports activation) if you need Deactivate semantics.
2. Remove the Deactivate call and rely on Region.Remove(view) if the view should disappear entirely.
3. Guard polymorphic code: only call Deactivate when the region actually supports it.
4. Keep the view in the region and manage visibility through your own mechanism if AllActiveRegion behavior is required.

Example fix

// before
region.Deactivate(myView); // region is AllActiveRegion -> throws
// after
if (region is AllActiveRegion)
    region.Remove(myView);
else
    region.Deactivate(myView);

if (region is AllActiveRegion)
    throw new InvalidOperationException("This region keeps all views active; Deactivate is not supported.");

bool SupportsDeactivate(IRegion region) => region is not AllActiveRegion;

try
{
    region.Deactivate(view);
}
catch (InvalidOperationException ex) when (region is AllActiveRegion)
{
    logger.LogWarning("Deactivate unsupported on AllActiveRegion; removing view instead.");
    region.Remove(view);
}

When it happens

Trigger: Calling region.Deactivate(view) on a region instance that is an AllActiveRegion — typically via IRegionManager region lookup, IRegion.ActiveViews manipulation, or view lifecycle code that assumes deactivation is supported.

Common situations: Tab-like UIs where developers expect to hide views but the region was registered with AllActiveRegion; code shared between regions of different kinds calling Deactivate polymorphically; migrating code from SingleActiveRegion to AllActiveRegion.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Resources.HostControlCannotBeSetAfterAttach
• Resources.HostControlCannotBeSetAfterAttach
• The HostControl property cannot be set after Attach method…
• The HostControl property cannot be set after Attach method…
• Cannot create navigation target

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/f846fb58addb13c1. Report an issue: GitHub.

Appendix: source

Thrown at src/Wpf/Prism.Wpf/Navigation/Regions/AllActiveRegion.cs:23

    /// <summary>
    /// Region that keeps all the views in it as active. Deactivation of views is not allowed.
    /// </summary>
    public class AllActiveRegion : Region
    {
        /// <summary>
        /// Gets a readonly view of the collection of all the active views in the region. These are all the added views.
        /// </summary>
        /// <value>An <see cref="IViewsCollection"/> of all the active views.</value>
        public override IViewsCollection ActiveViews => Views;

        /// <summary>
        /// Deactivate is not valid in this Region. This method will always throw <see cref="InvalidOperationException"/>.
        /// </summary>
        /// <param name="view">The view to deactivate.</param>
        /// <exception cref="InvalidOperationException">Every time this method is called.</exception>
        public override void Deactivate(object view)
        {
            throw new InvalidOperationException(Resources.DeactiveNotPossibleException);
        }
    }
}

View on GitHub (pinned to 358118cd64)