PrismLibrary/Prism · error · InvalidOperationException

Resources.CannotChangeRegionNameException

Error message

Resources.CannotChangeRegionNameException

What it means

Region.Name is immutable once set: the setter allows assignment only while _name is still null. If you assign a different non-null name to an already-initialized region, Prism throws InvalidOperationException with CannotChangeRegionNameException because region name identity is relied upon by RegionManager registration and navigation.

Solutions

  1. Remove the region (RegionManager.Regions.Remove) and recreate it with the new name instead of mutating Name.
  2. Set the region name exactly once at creation time and never reassign it; treat Name as read-only after initialization.
  3. If the region came from XAML, change the RegionName attribute in the view and let a fresh region be created, rather than setting Name in code.

Example fix

// before
region.Name = "NewRegionName"; // throws if already named
// after
regionManager.Regions.Remove("OldRegionName");
var newRegion = new Region { Name = "NewRegionName" };
regionManager.Regions.Add(newRegion);
Defensive patterns

Strategy: validation

Validate before calling

if (region.Name != null && region.Name != newName)
    throw new InvalidOperationException("Region names cannot change after assignment.");
region.Name = newName;

Try / catch

try
{
    region.Name = newName;
}
catch (InvalidOperationException)
{
    // recreate the region with the new name instead
}

Prevention

When it happens

Trigger: Setting Region.Name (directly or via XAML RegionManager.RegionName) to a value different from the already-assigned name of a live region, e.g. renaming a region after the region has been registered with the RegionManager.

Common situations: Renaming a region in XAML while reusing a cached/custom region; programmatically reconfiguring regions created by a previous app state; copy-pasting a control template and editing RegionName at runtime instead of recreating the region.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/a3f7546b361bc9cd. Report an issue: GitHub.

Appendix: source

Thrown at src/Wpf/Prism.Wpf/Navigation/Regions/Region.cs:77

                    _context = value;
                    OnPropertyChanged(nameof(Context));
                }
            }
        }

        /// <summary>
        /// Gets the name of the region that uniquely identifies the region within a <see cref="IRegionManager"/>.
        /// </summary>
        /// <value>The name of the region.</value>
        public string Name
        {
            get => _name;

            set
            {
                if (_name != null && _name != value)
                {
                    throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, Resources.CannotChangeRegionNameException, _name));
                }

                if (string.IsNullOrEmpty(value))
                {
                    throw new ArgumentException(Resources.RegionNameCannotBeEmptyException);
                }

                _name = value;
                OnPropertyChanged(nameof(Name));
            }
        }

        /// <summary>
        /// Gets a readonly view of the collection of views in the region.
        /// </summary>
        /// <value>An <see cref="IViewsCollection"/> of all the added views.</value>
        public virtual IViewsCollection Views
        {

View on GitHub (pinned to 358118cd64)