Construction of `AccessibleObject` forces creation of `Handle`

• .NET Core Version: .NET 5 P4

Problem description:

Multiple code paths involving a construction or an interaction with an AccessibleObject on a control that hasn’t had its Handle created cause the creation of the Handle. This may lead to undesired side-effects like described in https://github.com/dotnet/winforms/issues/2797.

Expected behavior:

None of AccessibleObject events must be raised if an owner control doesn’t have a valid `Handle. https://github.com/dotnet/winforms/blob/b666dc7a94d8ac87a7d300cfb4fa86332fb79bae/src/System.Windows.Forms/src/System/Windows/Forms/AccessibleObject.cs#L2227-L2294

Minimal repro:

Run the following test: https://github.com/dotnet/winforms/blob/b666dc7a94d8ac87a7d300cfb4fa86332fb79bae/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ToolStripItemTests.cs#L14005-L14022

Line:14014 will cause ToolStripItem.Handle to be created.

 	System.Windows.Forms.dll!System.Windows.Forms.Control.CreateHandle() Line 4912	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.Control.Handle.get() Line 2464	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.Control.ControlAccessibleObject.ControlAccessibleObject(System.Windows.Forms.Control ownerControl = {System.Windows.Forms.ToolStrip}) Line 32	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.ToolStrip.ToolStripAccessibleObject.ToolStripAccessibleObject(System.Windows.Forms.ToolStrip owner = {System.Windows.Forms.ToolStrip}) Line 5016	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.ToolStrip.CreateAccessibilityInstance() Line 4985	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.Control.AccessibilityObject.get() Line 498	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.ToolStripItem.ToolStripItemAccessibleObject.FragmentRoot.get() Line 364	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.AccessibleObject.Interop.UiaCore.IRawElementProviderFragment.FragmentRoot.get() Line 819	C#	Symbols loaded.
 	[Native to Managed Transition]		Annotated Frame
 	[Managed to Native Transition]		Annotated Frame
 	System.Windows.Forms.dll!System.Windows.Forms.AccessibleObject.RaiseAutomationEvent(Interop.UiaCore.UIA eventId = AutomationFocusChangedEventId) Line 2267	C#	Symbols loaded.
>	System.Windows.Forms.dll!System.Windows.Forms.ToolStripItem.ToolStripItemAccessibleObject.RaiseFocusChanged() Line 481	C#	Symbols loaded.
 	System.Windows.Forms.dll!System.Windows.Forms.ToolStripItem.Select() Line 3094	C#	Symbols loaded.
 	System.Windows.Forms.Tests.dll!System.Windows.Forms.Tests.ToolStripItemTests.ToolStripItem_Select_InvokeWithParent_Success() Line 14017	C#	Symbols loaded.

[RussKie]

We could, for example, add the following guard and then run tests:

diff --git a/src/System.Windows.Forms/src/System/Windows/Forms/Control.ControlAccessibleObject.cs b/src/System.Windows.Forms/src/System/Windows/Forms/Control.ControlAccessibleObject.cs
index b1bb53959..fa1699363 100644
--- a/src/System.Windows.Forms/src/System/Windows/Forms/Control.ControlAccessibleObject.cs
+++ b/src/System.Windows.Forms/src/System/Windows/Forms/Control.ControlAccessibleObject.cs
@@ -29,6 +29,12 @@ namespace System.Windows.Forms
             public ControlAccessibleObject(Control ownerControl)
             {
                 Owner = ownerControl ?? throw new ArgumentNullException(nameof(ownerControl));
+
+                if (!ownerControl.IsHandleCreated)
+                {
+                    Debug.Fail("Accessibility object must not be created for a control without a valid handle");
+                }
+
                 IntPtr handle = ownerControl.Handle;
                 Handle = handle;
             }

This guard will crash the test runner, highlighting the paths where we fire off accessibility events on controls without valid handles.

Would this be a correct approach?

[vladimir-krestov]

We don’t need to change Handle.get because _handle is set when creating control Handle (OnHandleCreated method). And if Handle is created then (Owner.Handle == _handle).