Fixes #1984. Added ClearOnVisibleFalse to flag if the view must be cleared or not.

Author: BDisp

Terminal.Gui/Core/View.cs

@@ -1820,7 +1820,7 @@ public void ClearKeybinding (Key key)
 		/// <param name="command"></param>
 		public void ClearKeybinding (params Command [] command)
 		{
-			foreach (var kvp in KeyBindings.Where (kvp => kvp.Value.SequenceEqual (command)).ToArray()) {
+			foreach (var kvp in KeyBindings.Where (kvp => kvp.Value.SequenceEqual (command)).ToArray ()) {
 				KeyBindings.Remove (kvp.Key);
 			}
 		}
@@ -2556,6 +2556,11 @@ public override bool Enabled {
 			}
 		}
 
+		/// <summary>
+		/// Gets or sets whether a view is cleared if the <see cref="Visible"/> property is <see langword="false"/>.
+		/// </summary>
+		public bool ClearOnVisibleFalse { get; set; } = true;
+
 		/// <inheritdoc/>>
 		public override bool Visible {
 			get => base.Visible;
@@ -2566,7 +2571,9 @@ public override bool Visible {
 						if (HasFocus) {
 							SetHasFocus (false, this);
 						}
-						Clear ();
+						if (ClearOnVisibleFalse) {
+							Clear ();
+						}
 					}
 					OnVisibleChanged ();
 					SetNeedsDisplay ();

UnitTests/ViewTests.cs

@@ -3830,6 +3830,66 @@ public void Visible_Clear_The_View_Output ()
 │                            │
 │                            │
 └────────────────────────────┘
+", output);
+		}
+
+		[Fact, AutoInitShutdown]
+		public void ClearOnVisibleFalse_Gets_Sets ()
+		{
+			var text = "This is a test\nThis is a test\nThis is a test\nThis is a test\nThis is a test\nThis is a test";
+			var label = new Label (text);
+			Application.Top.Add (label);
+
+			var sbv = new ScrollBarView (label, true, false) {
+				Size = 100,
+				ClearOnVisibleFalse = false
+			};
+			Application.Begin (Application.Top);
+
+			Assert.True (sbv.Visible);
+			GraphViewTests.AssertDriverContentsWithFrameAre (@"
+This is a tes▲
+This is a tes┬
+This is a tes┴
+This is a tes░
+This is a tes░
+This is a tes▼
+", output);
+
+			sbv.Visible = false;
+			Assert.False (sbv.Visible);
+			Application.Top.Redraw (Application.Top.Bounds);
+			GraphViewTests.AssertDriverContentsWithFrameAre (@"
+This is a test
+This is a test
+This is a test
+This is a test
+This is a test
+This is a test
+", output);
+
+			sbv.Visible = true;
+			Assert.True (sbv.Visible);
+			Application.Top.Redraw (Application.Top.Bounds);
+			GraphViewTests.AssertDriverContentsWithFrameAre (@"
+This is a tes▲
+This is a tes┬
+This is a tes┴
+This is a tes░
+This is a tes░
+This is a tes▼
+", output);
+
+			sbv.ClearOnVisibleFalse = true;
+			sbv.Visible = false;
+			Assert.False (sbv.Visible);
+			GraphViewTests.AssertDriverContentsWithFrameAre (@"
+This is a tes
+This is a tes
+This is a tes
+This is a tes
+This is a tes
+This is a tes
 ", output);
 		}
 	}