Fix issue 15031: Disable NET11 VisualStylesMode for composite controls (ToolStrip, DataGridView, etc.) until NET11 layout modernization is completed

src/System.Windows.Forms/System/Windows/Forms/Control.cs

@@ -899,10 +899,10 @@ public virtual partial VisualStylesMode VisualStylesMode
 
             VisualStylesMode oldEffectiveValue = EffectiveVisualStylesMode;
 
-            // Inherit was requested explicitly, or the requested value matches the ambient (parent) value:
+            // Inherit was requested explicitly, or the requested value matches the uncoerced ambient value:
             // drop any local override so the value is inherited again.
             if (value == VisualStylesMode.Inherit
-                || (ParentInternal is { } parent && parent.ResolvedVisualStylesMode == value))
+                || (ParentInternal is { } parent && parent.UncoercedVisualStylesMode == value))
             {
                 Properties.RemoveValue(s_visualStylesModeProperty);
             }
@@ -927,18 +927,30 @@ private bool ShouldSerializeVisualStylesMode()
     private void ResetVisualStylesMode()
         => VisualStylesMode = VisualStylesMode.Inherit;
 
-    private VisualStylesMode ResolvedVisualStylesMode
+    private VisualStylesMode UncoercedVisualStylesMode
     {
         get
         {
             VisualStylesMode value = VisualStylesMode;
 
             return value == VisualStylesMode.Inherit
-                ? ParentInternal?.ResolvedVisualStylesMode ?? DefaultVisualStylesMode
+                ? ParentInternal?.UncoercedVisualStylesMode ?? DefaultVisualStylesMode
                 : value;
         }
     }
 
+    private VisualStylesMode ResolvedVisualStylesMode
+        => GetSupportedVisualStylesMode(
+            VisualStylesMode == VisualStylesMode.Inherit
+                ? ParentInternal?.ResolvedVisualStylesMode ?? DefaultVisualStylesMode
+                : VisualStylesMode);
+
+    /// <summary>
+    ///  Coerces a requested visual styles mode to one supported by this control.
+    /// </summary>
+    private protected virtual VisualStylesMode GetSupportedVisualStylesMode(VisualStylesMode mode)
+        => mode;
+
     /// <summary>
     ///  Gets the renderer-authoritative <see cref="Forms.VisualStylesMode"/> that controls must honor when deciding
     ///  <see cref="CreateParams"/> or paint behavior, after applying the High Contrast and disabled clamps.
@@ -7446,28 +7458,60 @@ protected virtual void OnParentVisualStylesModeChanged(EventArgs e)
             return;
         }
 
+        VisualStylesModeChangeEventArgs? transition = e as VisualStylesModeChangeEventArgs;
+        if (transition is not null
+            && (!transition.IsCurrent
+                || ParentInternal?.EffectiveVisualStylesMode != transition.NewEffectiveVisualStylesMode))
+        {
+            return;
+        }
+
         if (Properties.ContainsKey(s_visualStylesModeProperty))
         {
             if (Properties.GetValueOrDefault<VisualStylesMode>(s_visualStylesModeProperty)
-                == ParentInternal?.ResolvedVisualStylesMode)
+                != ParentInternal?.UncoercedVisualStylesMode)
             {
-                // Same as the parent value, make it ambient again by removing it.
-                Properties.RemoveValue(s_visualStylesModeProperty);
+                // A local value isolates this subtree from parent changes.
+                return;
+            }
+
+            VisualStylesMode oldEffectiveVisualStylesMode = EffectiveVisualStylesMode;
+
+            // Same as the parent value, make it ambient again by removing it.
+            Properties.RemoveValue(s_visualStylesModeProperty);
+
+            VisualStylesMode newEffectiveVisualStylesMode = EffectiveVisualStylesMode;
+            if (oldEffectiveVisualStylesMode == newEffectiveVisualStylesMode)
+            {
+                return;
             }
 
-            // A local value isolates this subtree from parent changes. If the local value matched the
-            // parent's new value, removing it preserves the effective value while making it ambient again.
+            OnVisualStylesModeChanged(
+                transition?.CreateForControl(
+                    this,
+                    oldEffectiveVisualStylesMode,
+                    newEffectiveVisualStylesMode)
+                ?? e);
+
             return;
         }
 
-        if (e is VisualStylesModeChangeEventArgs transition
-            && (!transition.IsCurrent
-                || ParentInternal?.EffectiveVisualStylesMode != transition.NewEffectiveVisualStylesMode))
+        if (transition is not null)
         {
+            VisualStylesModeChangeEventArgs transitionForControl = transition.CreateForControl(this);
+            if (transitionForControl.OldEffectiveVisualStylesMode
+                != transitionForControl.NewEffectiveVisualStylesMode)
+            {
+                OnVisualStylesModeChanged(transitionForControl);
+            }
+            else if (ChildControls is { } children)
+            {
+                CascadeVisualStylesModeChanged(children, transitionForControl, transitionForControl);
+            }
+
             return;
         }
 
-        // In every other case we're going to raise the event.
         OnVisualStylesModeChanged(e);
     }
 
@@ -7534,19 +7578,34 @@ public bool IsCurrent
 
         public VisualStylesModeChangeEventArgs CreateForControl(Control control)
         {
-            if (SystemVisualSettingsTransition is not { } systemVisualSettingsTransition)
+            if (SystemVisualSettingsTransition is { } systemVisualSettingsTransition)
             {
-                return this;
+                return new(
+                    _state,
+                    control,
+                    control.Properties.GetValueOrDefault(s_visualStylesModeChangeVersionProperty, 0),
+                    control.GetEffectiveVisualStylesMode(systemVisualSettingsTransition.OldSettings.HighContrastEnabled),
+                    control.GetEffectiveVisualStylesMode(systemVisualSettingsTransition.NewSettings.HighContrastEnabled),
+                    systemVisualSettingsTransition);
             }
 
-            return new(
+            return CreateForControl(
+                control,
+                control.GetSupportedVisualStylesMode(OldEffectiveVisualStylesMode),
+                control.GetSupportedVisualStylesMode(NewEffectiveVisualStylesMode));
+        }
+
+        public VisualStylesModeChangeEventArgs CreateForControl(
+            Control control,
+            VisualStylesMode oldEffectiveVisualStylesMode,
+            VisualStylesMode newEffectiveVisualStylesMode)
+            => new(
                 _state,
                 control,
                 control.Properties.GetValueOrDefault(s_visualStylesModeChangeVersionProperty, 0),
-                control.GetEffectiveVisualStylesMode(systemVisualSettingsTransition.OldSettings.HighContrastEnabled),
-                control.GetEffectiveVisualStylesMode(systemVisualSettingsTransition.NewSettings.HighContrastEnabled),
-                systemVisualSettingsTransition);
-        }
+                oldEffectiveVisualStylesMode,
+                newEffectiveVisualStylesMode,
+                systemVisualSettingsTransition: null);
 
         public void PerformLayouts()
         {

src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridView.cs

@@ -16,6 +16,9 @@ namespace System.Windows.Forms;
 [SRDescription(nameof(SR.DescriptionDataGridView))]
 public partial class DataGridView : Control, ISupportInitialize
 {
+    private protected override VisualStylesMode GetSupportedVisualStylesMode(VisualStylesMode mode)
+        => mode >= VisualStylesMode.Net11 ? VisualStylesMode.Classic : mode;
+
     private static readonly object s_allowUserToAddRowsChangedEvent = new();
     private static readonly object s_allowUserToDeleteRowsChangedEvent = new();
     private static readonly object s_allowUserToOrderColumnsChangedEvent = new();

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStrip.cs

@@ -23,6 +23,9 @@ namespace System.Windows.Forms;
 [DefaultEvent(nameof(ItemClicked))]
 public partial class ToolStrip : ScrollableControl, IArrangedElement, ISupportToolStripPanel
 {
+    private protected override VisualStylesMode GetSupportedVisualStylesMode(VisualStylesMode mode)
+        => mode >= VisualStylesMode.Net11 ? VisualStylesMode.Classic : mode;
+
     private static Size s_onePixel = new(1, 1);
     internal static Point s_invalidMouseEnter = new(int.MaxValue, int.MaxValue);
 

src/test/unit/System.Windows.Forms/System/Windows/Forms/ControlTests.VisualStylesMode.cs

@@ -496,6 +496,33 @@ public void Control_VisualStylesMode_ReentrantChange_SuppressesStaleChildCascade
         Assert.Equal(1, childChangedCallCount);
     }
 
+    [WinFormsFact]
+    public void Control_VisualStylesMode_LocalOverrideRemovedByCoercedParent_RaisesChangedAndCascades()
+    {
+        using DataGridView parent = new() { VisualStylesMode = VisualStylesMode.Disabled };
+        using SubControlWithVisualStyles child = new()
+        {
+            HighContrast = false,
+            VisualStylesMode = VisualStylesMode.Latest
+        };
+        using SubControlWithVisualStyles grandchild = new() { HighContrast = false };
+        child.Controls.Add(grandchild);
+        parent.Controls.Add(child);
+
+        int childChangedCallCount = 0;
+        child.VisualStylesModeChanged += (sender, e) => childChangedCallCount++;
+        int grandchildChangedCallCount = 0;
+        grandchild.VisualStylesModeChanged += (sender, e) => grandchildChangedCallCount++;
+
+        parent.VisualStylesMode = VisualStylesMode.Latest;
+
+        Assert.Equal(VisualStylesMode.Inherit, child.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, child.EffectiveVisualStylesModeAccessor);
+        Assert.Equal(VisualStylesMode.Classic, grandchild.EffectiveVisualStylesModeAccessor);
+        Assert.Equal(1, childChangedCallCount);
+        Assert.Equal(1, grandchildChangedCallCount);
+    }
+
     [WinFormsFact]
     public void Appearance_ToggleSwitch_HasExpectedValue()
     {

src/test/unit/System.Windows.Forms/System/Windows/Forms/DataGridViewTests.cs

@@ -38,6 +38,61 @@ public void DataGridView_Ctor_Default()
         Assert.Same(control.RowTemplate, control.RowTemplate);
     }
 
+    [WinFormsTheory]
+    [InlineData(VisualStylesMode.Net11)]
+    [InlineData(VisualStylesMode.Latest)]
+    public void DataGridView_VisualStylesMode_ModernMode_UsesClassicEffectiveMode(VisualStylesMode value)
+    {
+        using SubDataGridView control = new() { VisualStylesMode = value };
+
+        Assert.Equal(value, control.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+        Assert.False(control.IsHandleCreated);
+    }
+
+    [WinFormsTheory]
+    [InlineData(VisualStylesMode.Net11)]
+    [InlineData(VisualStylesMode.Latest)]
+    public void DataGridView_VisualStylesMode_InheritedModernMode_UsesClassicEffectiveMode(VisualStylesMode value)
+    {
+        using Control parent = new() { VisualStylesMode = value };
+        using SubDataGridView control = new();
+        parent.Controls.Add(control);
+
+        Assert.Equal(VisualStylesMode.Inherit, control.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+        Assert.False(control.IsHandleCreated);
+    }
+
+    [WinFormsFact]
+    public void DataGridView_VisualStylesMode_ParentChangesToModernMode_DoesNotRaiseChanged()
+    {
+        using Control parent = new() { VisualStylesMode = VisualStylesMode.Classic };
+        using SubDataGridView control = new();
+        parent.Controls.Add(control);
+        int callCount = 0;
+        control.VisualStylesModeChanged += (sender, e) => callCount++;
+
+        parent.VisualStylesMode = VisualStylesMode.Net11;
+
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+        Assert.Equal(0, callCount);
+    }
+
+    [WinFormsFact]
+    public void DataGridView_VisualStylesMode_ExplicitClassic_RemainsLocalOverride()
+    {
+        using Control parent = new() { VisualStylesMode = VisualStylesMode.Net11 };
+        using SubDataGridView control = new();
+        parent.Controls.Add(control);
+        control.VisualStylesMode = VisualStylesMode.Classic;
+
+        parent.VisualStylesMode = VisualStylesMode.Disabled;
+
+        Assert.Equal(VisualStylesMode.Classic, control.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+    }
+
     private const int DefaultColumnHeadersHeight = 23;
 
     public static IEnumerable<object[]> ColumnHeadersHeight_Set_TestData()
@@ -2892,6 +2947,8 @@ private class SubDataGridViewCell : DataGridViewCell
 
     private class SubDataGridView : DataGridView
     {
+        public VisualStylesMode EffectiveVisualStylesModeAccessor => base.EffectiveVisualStylesMode;
+
         public new void OnColumnHeadersHeightChanged(EventArgs e) => base.OnColumnHeadersHeightChanged(e);
 
         public new void OnColumnHeadersHeightSizeModeChanged(DataGridViewAutoSizeModeEventArgs e) => base.OnColumnHeadersHeightSizeModeChanged(e);

src/test/unit/System.Windows.Forms/System/Windows/Forms/ToolStripTests.cs

@@ -16,6 +16,61 @@ namespace System.Windows.Forms.Tests;
 
 public partial class ToolStripTests : IDisposable
 {
+    [WinFormsTheory]
+    [InlineData(VisualStylesMode.Net11)]
+    [InlineData(VisualStylesMode.Latest)]
+    public void ToolStrip_VisualStylesMode_ModernMode_UsesClassicEffectiveMode(VisualStylesMode value)
+    {
+        using SubToolStrip control = new() { VisualStylesMode = value };
+
+        Assert.Equal(value, control.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+        Assert.False(control.IsHandleCreated);
+    }
+
+    [WinFormsTheory]
+    [InlineData(VisualStylesMode.Net11)]
+    [InlineData(VisualStylesMode.Latest)]
+    public void ToolStrip_VisualStylesMode_InheritedModernMode_UsesClassicEffectiveMode(VisualStylesMode value)
+    {
+        using Control parent = new() { VisualStylesMode = value };
+        using SubToolStrip control = new();
+        parent.Controls.Add(control);
+
+        Assert.Equal(VisualStylesMode.Inherit, control.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+        Assert.False(control.IsHandleCreated);
+    }
+
+    [WinFormsFact]
+    public void ToolStrip_VisualStylesMode_ParentChangesToModernMode_DoesNotRaiseChanged()
+    {
+        using Control parent = new() { VisualStylesMode = VisualStylesMode.Classic };
+        using SubToolStrip control = new();
+        parent.Controls.Add(control);
+        int callCount = 0;
+        control.VisualStylesModeChanged += (sender, e) => callCount++;
+
+        parent.VisualStylesMode = VisualStylesMode.Net11;
+
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+        Assert.Equal(0, callCount);
+    }
+
+    [WinFormsFact]
+    public void ToolStrip_VisualStylesMode_ExplicitClassic_RemainsLocalOverride()
+    {
+        using Control parent = new() { VisualStylesMode = VisualStylesMode.Net11 };
+        using SubToolStrip control = new();
+        parent.Controls.Add(control);
+        control.VisualStylesMode = VisualStylesMode.Classic;
+
+        parent.VisualStylesMode = VisualStylesMode.Disabled;
+
+        Assert.Equal(VisualStylesMode.Classic, control.VisualStylesMode);
+        Assert.Equal(VisualStylesMode.Classic, control.EffectiveVisualStylesModeAccessor);
+    }
+
     [WinFormsFact]
     public void ToolStrip_Ctor_Default()
     {
@@ -7537,6 +7592,8 @@ public SubToolStrip(ToolStripItem[] items) : base(items)
 
         public new bool CanRaiseEvents => base.CanRaiseEvents;
 
+        public VisualStylesMode EffectiveVisualStylesModeAccessor => base.EffectiveVisualStylesMode;
+
         public new CreateParams CreateParams => base.CreateParams;
 
         public new Cursor DefaultCursor => base.DefaultCursor;