public RegisteredPackageSourcesViewModel(
            IPackageSourceProvider packageSourceProvider,
            IFolderBrowser folderBrowser,
            PackageSourceViewModelChecker packageSourceChecker)
        {
            this.packageSourceProvider = packageSourceProvider;
            this.folderBrowser         = folderBrowser;
            this.packageSourceChecker  = packageSourceChecker;

            if (packageSourceChecker != null)
            {
                packageSourceChecker.PackageSourceChecked += PackageSourceChecked;
            }

            CreateCommands();
        }