C# how to use createtextservices correctly and inherit the itexthost interface?

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C#

WinForms

RichTextBox

I want to implement a windowless rich text box, but the example I found is only C++.
Now I have completed most of the code with C#. The only problem is that the function CreateTextServices has BUG (Win10x64 is ok, Win7x86 is error):

protected override void OnHandleCreated(EventArgs e)
{
	base.OnHandleCreated(e);
	try
	{
		IntPtr pUnk = IntPtr.Zero;
		if (WinAPI.CreateTextServices(IntPtr.Zero, this, out pUnk) < 0)
			throw new Win32Exception();

		//Guid iid = typeof(WinInterface.ITextServices).GUID;
		//Marshal.QueryInterface(pUnk, ref iid, out ppv);
		//services = (WinInterface.ITextServices)
		//    Marshal.GetTypedObjectForIUnknown(ppv, typeof(WinInterface.ITextServices));

	}
	finally
	{
		//Marshal.Release(pUnk);
	}
}
[DllImport(ExternDll.Msftedit, SetLastError = true, CharSet = CharSet.Auto)]
public static extern int CreateTextServices(
			IntPtr punkOuter,
			WinInterface.ITextHost pITextHost,
			out IntPtr ppUnk
			);

On win7x86 it always throws a FatalExecutionEngineError exception.
Can someone help me? Thank you

What I have tried:

I modified the function parameter values of the ITextHost, but they have no effect.