Fixes #5040. SelectorBase.TabBehavior setter calls CreateSubViews() without UpdateChecked(), desyncing CheckBox visual state

Terminal.Gui/Views/Selectors/OptionSelector.cs

@@ -135,15 +135,42 @@ private void Cycle ()
     ///     Updates the checked state of all checkbox subviews so that only the checkbox corresponding
     ///     to the current <see cref="SelectorBase.Value"/> is checked.
     /// </summary>
+    /// <remarks>
+    ///     If <see cref="SelectorBase.Value"/> doesn't exist in the list of checkbox values, then the first checkbox will be checked by default
+    ///     and will raise the <see cref="SelectorBase.ValueChanging"/>/<see cref="SelectorBase.ValueChanged"/> events.
+    /// </remarks>
     public override void UpdateChecked ()
     {
+        Dictionary<CheckBox, int> checkBoxValueMap = SubViews.OfType<CheckBox> ().ToDictionary (cb => cb, GetCheckBoxValue);
+
         foreach (CheckBox cb in SubViews.OfType<CheckBox> ())
         {
             int value = GetCheckBoxValue (cb);
 
             cb.Value = value == Value ? CheckState.Checked : CheckState.UnChecked;
         }
 
+        // If Value doesn't exist in any checkbox, use the first checkbox's value
+        if (Value is not null && checkBoxValueMap.Count > 0 && Values!.All (v => v != Value) && checkBoxValueMap.Values.All (v => v != Value))
+        {
+            Value = checkBoxValueMap.Values.First ();
+
+            foreach (KeyValuePair<CheckBox, int> kvp in checkBoxValueMap)
+            {
+                if (kvp.Value != Value)
+                {
+                    continue;
+                }
+                kvp.Key.Value = CheckState.Checked;
+
+                break;
+            }
+
+            // Sanity checks to verify the assumptions above
+            Debug.Assert (checkBoxValueMap.Values.First () != (int)SubViews.OfType<CheckBox> ().First ().Value);
+            Debug.Assert (checkBoxValueMap.Values.First () == Values! [0]);
+        }
+
         // Verify at most one is checked
         Debug.Assert (SubViews.OfType<CheckBox> ().Count (cb => cb.Value == CheckState.Checked) <= 1);
     }

Terminal.Gui/Views/Selectors/SelectorBase.cs

@@ -156,7 +156,6 @@ public SelectorStyles Styles
             field = value;
 
             CreateSubViews ();
-            UpdateChecked ();
         }
     }
 
@@ -316,7 +315,6 @@ public virtual IReadOnlyList<int>? Values
             }
 
             CreateSubViews ();
-            UpdateChecked ();
         }
     }
 
@@ -331,7 +329,6 @@ public IReadOnlyList<string>? Labels
             field = value;
 
             CreateSubViews ();
-            UpdateChecked ();
         }
     }
 
@@ -436,6 +433,9 @@ public virtual void CreateSubViews ()
         // Note: Hotkey assignment is now handled automatically by the base class
         // when SubViews are added via Add(). No need to call AssignUniqueHotKeys() here.
         SetLayout ();
+
+        // Ensure the checked state of the checkboxes is correct after recreating subviews
+        UpdateChecked ();
     }
 
     /// <summary>

Tests/UnitTestsParallelizable/Views/SelectorBaseTests.cs

@@ -598,6 +598,61 @@ public void CreateSubViews_SetsCheckBoxProperties ()
         Assert.True (checkBox.CanFocus);
     }
 
+    [Fact]
+    public void CreateSubViews_ResetsValue_WhenCurrentValueNotInNewValues ()
+    {
+        OptionSelector selector = new ();
+
+        selector.Labels = ["Option1", "Option2"];
+        selector.Values = [10, 20];
+
+        // Verify initial value is set to first value (10)
+        Assert.Equal (10, selector.Value);
+
+        // Change to new labels/values where current value (10) is not present
+        selector.Labels = ["New1", "New2"];
+        selector.Values = [30, 40];
+
+        // Value should reset to first value (30)
+        Assert.Equal (30, selector.Value);
+    }
+
+    [Fact]
+    public void Setting_TabBehavior_AfterSubViewsAreCreated_DoesNotLoseCheckedState ()
+    {
+        OptionSelector selector = new ()
+        {
+            Labels = ["Option1", "Option2"], Values = [10, 20], Orientation = Orientation.Vertical, TabBehavior = TabBehavior.NoStop
+        };
+
+        List<CheckBox> checkBoxes = [.. selector.SubViews.OfType<CheckBox> ()];
+
+        Assert.Equal (2, checkBoxes.Count);
+        Assert.Equal (CheckState.Checked, checkBoxes [0].Value);
+        Assert.Equal (CheckState.UnChecked, checkBoxes [1].Value);
+        Assert.Equal (10, selector.Value);
+        Assert.Equal (TabBehavior.NoStop, selector.TabBehavior);
+    }
+
+    [Fact]
+    public void Setting_TabBehavior_AfterSubViewsAreCreated_DoesNotLoseCheckedState_With_Enum ()
+    {
+        OptionSelector<Side> selector = new ()
+        {
+            Orientation = Orientation.Vertical, TabBehavior = TabBehavior.NoStop
+        };
+
+        List<CheckBox> checkBoxes = [.. selector.SubViews.OfType<CheckBox> ()];
+
+        Assert.Equal (4, checkBoxes.Count);
+        Assert.Equal (CheckState.Checked, checkBoxes [0].Value);
+        Assert.Equal (CheckState.UnChecked, checkBoxes [1].Value);
+        Assert.Equal (CheckState.UnChecked, checkBoxes [2].Value);
+        Assert.Equal (CheckState.UnChecked, checkBoxes [3].Value);
+        Assert.Equal (Side.Left, selector.Value);
+        Assert.Equal (TabBehavior.NoStop, selector.TabBehavior);
+    }
+
     #endregion
 
     #region HotKey Command Tests