Proper cancel logic in installer

MediaBrowser.Installer/MainWindow.xaml.cs

@@ -30,6 +30,8 @@ namespace MediaBrowser.Installer
 
         protected string TempLocation = Path.Combine(Path.GetTempPath(), "MediaBrowser");
 
+        protected WebClient MainClient = new WebClient();
+
         public MainWindow()
         {
             GetArgs();
@@ -48,6 +50,15 @@ namespace MediaBrowser.Installer
             {
                 e.Cancel = true;
             }
+            if (MainClient.IsBusy)
+            {
+                MainClient.CancelAsync();
+                while (MainClient.IsBusy)
+                {
+                    // wait to finish
+                }
+            }
+            MainClient.Dispose();
             ClearTempLocation(TempLocation);
             base.OnClosing(e);
         }
@@ -129,6 +140,8 @@ namespace MediaBrowser.Installer
             dlAnimation.StopAnimation();
             prgProgress.Visibility = btnCancel.Visibility = Visibility.Hidden;
 
+            if (archive == null) return;  //we canceled or had an error that was already reported
+
             // Extract
             lblStatus.Content = "Extracting Package...";
             try 
@@ -166,13 +179,11 @@ namespace MediaBrowser.Installer
         }
 
         protected async Task<PackageVersionInfo> GetPackageVersion()
-        {
-            using (var client = new WebClient())
         {
             try
             {
                 // get the package information for the server
-                    var json = await client.DownloadStringTaskAsync("http://www.mb3admin.com/admin/service/package/retrieveAll?name=" + PackageName);
+                var json = await MainClient.DownloadStringTaskAsync("http://www.mb3admin.com/admin/service/package/retrieveAll?name=" + PackageName);
                 var packages = JsonSerializer.DeserializeFromString<List<PackageInfo>>(json);
 
                 var version = packages[0].versions.Where(v => v.classification <= PackageClass).OrderByDescending(v => v.version).FirstOrDefault(v => v.version <= PackageVersion);
@@ -188,7 +199,6 @@ namespace MediaBrowser.Installer
                 SystemClose(e.GetType().FullName + "\n\n" + e.Message);
             }
 
-            }
             return null;
         }
 
@@ -197,23 +207,32 @@ namespace MediaBrowser.Installer
         /// </summary>
         /// <returns>The fully qualified name of the downloaded package</returns>
         protected async Task<string> DownloadPackage(PackageVersionInfo version)
-        {
-            using (var client = new WebClient())
         {
             try
             {
                 var archiveFile = Path.Combine(PrepareTempLocation(), version.targetFilename);
 
                 // setup download progress and download the package
-                    client.DownloadProgressChanged += DownloadProgressChanged;
+                MainClient.DownloadProgressChanged += DownloadProgressChanged;
-                    await client.DownloadFileTaskAsync(version.sourceUrl, archiveFile);
+                try
+                {
+                    await MainClient.DownloadFileTaskAsync(version.sourceUrl, archiveFile);
+                }
+                catch (WebException e)
+                {
+                    if (e.Status == WebExceptionStatus.RequestCanceled)
+                    {
+                        return null;
+                    }
+                    throw;
+                }
+
                 return archiveFile;
             }
             catch (Exception e)
             {
                 SystemClose(e.GetType().FullName + "\n\n" + e.Message);
             }
-            }
             return "";
 
         }