Added IsLoaded property to allow control if a change was done before or after the toplevel was loaded.

UnitTests/TopLevels/ToplevelTests.cs

@@ -1031,5 +1031,53 @@ namespace Terminal.Gui.TopLevelTests {
 			Application.Driver.GetCursorVisibility (out cursor);
 			Assert.Equal (CursorVisibility.Invisible, cursor);
 		}
+
+		[Fact, AutoInitShutdown]
+		public void IsLoaded_Application_Begin ()
+		{
+			var top = Application.Top;
+			Assert.False (top.IsLoaded);
+
+			Application.Begin (top);
+			Assert.True (top.IsLoaded);
+		}
+
+		[Fact, AutoInitShutdown]
+		public void IsLoaded_With_Sub_Toplevel_Application_Begin_NeedDisplay ()
+		{
+			var top = Application.Top;
+			var subTop = new Toplevel ();
+			var view = new View (new Rect (0, 0, 20, 10));
+			subTop.Add (view);
+			top.Add (subTop);
+
+			Assert.False (top.IsLoaded);
+			Assert.False (subTop.IsLoaded);
+			Assert.Equal (new Rect (0, 0, 20, 10), view.Frame);
+			Assert.Equal (new Rect (0, 0, 20, 10), view.NeedDisplay);
+
+			view.LayoutStarted += view_LayoutStarted;
+
+			void view_LayoutStarted (View.LayoutEventArgs e)
+			{
+				Assert.Equal (new Rect (0, 0, 20, 10), view.NeedDisplay);
+				view.LayoutStarted -= view_LayoutStarted;
+			}
+
+			Application.Begin (top);
+
+			Assert.True (top.IsLoaded);
+			Assert.True (subTop.IsLoaded);
+			Assert.Equal (new Rect (0, 0, 20, 10), view.Frame);
+
+			view.Frame = new Rect (1, 3, 10, 5);
+			Assert.Equal (new Rect (1, 3, 10, 5), view.Frame);
+			Assert.Equal (new Rect (0, 0, 20, 10), view.NeedDisplay);
+
+			view.Redraw (view.Bounds);
+			view.Frame = new Rect (1, 3, 10, 5);
+			Assert.Equal (new Rect (1, 3, 10, 5), view.Frame);
+			Assert.Equal (new Rect (1, 3, 10, 5), view.NeedDisplay);
+		}
 	}
 }