WPF程序设置扩展名类型文件默认打开程序（程序需要以管理员方式启动）

    public class Startup
    {
        [STAThread]
        public static void Main(string[] args)
        {            
            SingleInstanceApplicationWrapper wrapper = new SingleInstanceApplicationWrapper();
            wrapper.Run(args);           
        }
    }

    public class SingleInstanceApplicationWrapper : 
        Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase
    {        
        public SingleInstanceApplicationWrapper()
        {
            // Enable single-instance mode.
            this.IsSingleInstance = true;
        }

        // Create the WPF application class.
        private WpfApp app;
        protected override bool OnStartup(
            Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
        {            
            string extension = ".testDoc";
            string title = "SingleInstanceApplication";
            string extensionDescription = "A Test Document";
            // Uncomment this line to create the file registration.
            // In Windows Vista, you'll need to run the application
            // as an administrator.            
            FileRegistrationHelper.SetFileAssociation(
              extension, title + "." + extensionDescription);

            app = new WpfApp();
            app.Run();

            return false;
        }

        // Direct multiple instances
        protected override void OnStartupNextInstance(
            Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs e)
        {
            if (e.CommandLine.Count > 0)
            {                
                app.ShowDocument(e.CommandLine[0]);
            }
        }
    }

    public class WpfApp : System.Windows.Application
    {
        protected override void OnStartup(System.Windows.StartupEventArgs e)
        {
            base.OnStartup(e);
            
            // Load the main window.
            DocumentList list = new DocumentList();
            this.MainWindow = list;
            list.Show();

            // Load the document that was specified as an argument.
            if (e.Args.Length > 0) ShowDocument(e.Args[0]);
        }

        // An ObservableCollection is a List that provides notification
        // when items are added, deleted, or removed. It's preferred for data binding.
        private ObservableCollection<DocumentReference> documents = 
            new ObservableCollection<DocumentReference>();
        public ObservableCollection<DocumentReference> Documents
        {
            get { return documents; }
            set { documents = value; }
        }        

        public void ShowDocument(string filename)
        {
            try
            {                
                Document doc = new Document();
                DocumentReference docRef = new DocumentReference(doc, filename);
                doc.LoadFile(docRef);                
                doc.Owner = this.MainWindow;
                doc.Show();
                doc.Activate();
                Documents.Add(docRef);
            }
            catch
            {
                MessageBox.Show("Could not load document.");
            }
        }
    }   

 通过这种方式，下次默认双击这种类型的文件时你的程序就会被设置为默认启动软件。