dotnet/wpf · error · InvalidOperationException

PackageAlreadyExists

Error message

PackageAlreadyExists

What it means

PackageStore.AddPackage refuses duplicate registration: if _packages already contains an entry for the given key URI, it throws InvalidOperationException(SR.PackageAlreadyExists). Each pack authority URI may map to at most one Package in the global store.

Solutions

1. Call PackageStore.RemovePackage(uri) before re-adding, or check PackageStore.GetPackage(uri) != null first.
2. Use a unique authority per package instance (e.g. append a version segment to the pack URI).
3. Restructure startup so registration happens exactly once (guard with a flag).

Example fix

// before
PackageStore.AddPackage(uri, pkg);
// after
if (PackageStore.GetPackage(uri) != null) PackageStore.RemovePackage(uri);
PackageStore.AddPackage(uri, pkg);

if (PackageStore.GetPackage(uri) != null) PackageStore.RemovePackage(uri);

try { PackageStore.AddPackage(uri, pkg); }
catch (InvalidOperationException ex) when (ex.Message.Contains("already exists")) { PackageStore.RemovePackage(uri); PackageStore.AddPackage(uri, pkg); }

When it happens

Trigger: Calling PackageStore.AddPackage twice with the same Uri (e.g. the same pack://myapp:,,,/ key) without removing the first package.

Common situations: Re-initialization logic that registers a resource package on every startup/event without a matching RemovePackage; plugin reload paths re-registering the same authority.

Understand the failure class

Background: "already exists" / EEXIST / FileAlreadyExistsException: what the 'file already exists' error means and how to fix it — this error's family across 37 libraries.

Related errors

• NotAllowedPackageUri
• SR.UriMustBeAbsolute
• ' ' cannot contain the path delimiter: ' '.
• ' ' cannot start with the reserved character range…
• ' ' ID is not a valid XSD ID.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/4b15625c338ec814. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/IO/Packaging/PackageStore.cs:109

       
            if (PackUriHelper.ComparePackUri(packUri, BaseUriHelper.PackAppBaseUri) == 0 ||
                PackUriHelper.ComparePackUri(packUri, BaseUriHelper.SiteOfOriginBaseUri) == 0)
            {
                throw new ArgumentException(SR.NotAllowedPackageUri, nameof(uri));
            }

            ArgumentNullException.ThrowIfNull(package);

            lock (_globalLock)
            {
                if (_packages == null)
                {
                    _packages = new HybridDictionary(2);
                }

                if (_packages.Contains(uri))
                {
                    throw new InvalidOperationException(SR.PackageAlreadyExists);
                }
                
                _packages.Add(uri, package);
            }
        }

        /// <summary>
        /// Removes a uri, package pair from the package store.
        /// </summary>
        /// <param name="uri">key uri</param>
        /// <permission cref="EnvironmentPermission"></permission>
        /// <remarks>
        /// </remarks>
        public static void RemovePackage(Uri uri)
        {
            ValidatePackageUri(uri);

            lock (_globalLock)

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