[NuGet] Switch back to native toolkit to display license dialog

Use Xwt.Toolkit.NativeEngine to show the License Acceptance dialog.
Briefly switched to not using this because complicated license
expressions cannot have their hyperlinks clicked. However these
do not seem to be used in practice. The native version fixes
odd tearing of the list view in the UI, also the list scrolling
to the end, and not being able to resize the UI without displaying
it first.

Downside to this change is that hyperlinks in complicated license
expressions cannot be clicked since this is not supported by
XWT's Xamarin.Mac implementation of the Label.

Author: mrward

main/src/addins/MonoDevelop.PackageManagement/MonoDevelop.PackageManagement.Gui/LicenseAcceptanceDialog.cs

@@ -67,7 +67,7 @@ public LicenseAcceptanceDialog (LicenseAcceptanceViewModel viewModel)
 			packagesList.Spacing = 0;
 
 			scroll = new ScrollView (packagesList);
-			scroll.HorizontalScrollPolicy = ScrollPolicy.Automatic;
+			scroll.HorizontalScrollPolicy = ScrollPolicy.Never;
 			scroll.VerticalScrollPolicy = ScrollPolicy.Automatic;
 			scroll.BorderVisible = false;
 			scroll.BackgroundColor = Ide.Gui.Styles.BackgroundColor;
@@ -107,6 +107,23 @@ void AddPackages ()
 			}
 		}
 
+		protected override void OnShown ()
+		{
+			var count = packagesList.Children.Count ();
+			if (count > 0 && count < 4) {
+				scroll.VerticalScrollPolicy = ScrollPolicy.Never;
+				var firstRow = packagesList.Children.First ();
+				var rowHeight = firstRow.Size.Height;
+				Height -= (rowHeight + firstRow.MarginTop + firstRow.MarginBottom) * (4 - count);
+			} else if (count == 4) {
+				scroll.VerticalScrollPolicy = ScrollPolicy.Never;
+			} else if (count > 4) {
+				scroll.VerticalScrollPolicy = ScrollPolicy.Automatic;
+				Height += rowMargin.Top + rowMargin.Bottom;
+			}
+			base.OnShown ();
+		}
+
 		void AddPackage (PackageLicenseViewModel package)
 		{
 			var titleBox = new VBox ();

main/src/addins/MonoDevelop.PackageManagement/MonoDevelop.PackageManagement/LicenseAcceptanceService.cs

@@ -51,13 +51,13 @@ Task<bool> ShowLicenseAcceptanceDialog (IEnumerable<NuGetPackageLicense> license
 		{
 			var res = new TaskCompletionSource<bool> ();
 			IdeApp.RunWhenIdle (() => {
-				// Disable use of native toolkit since hyperlinks cannot be clicked with the Xamarin.Mac LabelBackend
-				// Also scrollbars are always visible even when they are not needed.
-				//Xwt.Toolkit.NativeEngine.Invoke (delegate {
+				// Note that using native toolkit means hyperlinks from complicated license expressions cannot be
+				// clicked with the Xamarin.Mac LabelBackend
+				Xwt.Toolkit.NativeEngine.Invoke (delegate {
 					using (LicenseAcceptanceDialog dialog = CreateLicenseAcceptanceDialog (licenses)) {
 						res.SetResult (dialog.Run (MessageService.RootWindow));
 					}
-				//});
+				});
 			});
 			return res.Task;
 		}