Improve support for multiselect list box accessibility on Windows.

base/win/enum_variant.h

Index: base/win/enum_variant.h
===================================================================
--- base/win/enum_variant.h	(revision 0)
+++ base/win/enum_variant.h	(revision 0)
@@ -0,0 +1,53 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_WIN_ENUM_VARIANT_H_
+#define BASE_WIN_ENUM_VARIANT_H_
+#pragma once
+
+#include <unknwn.h>
+
+#include "base/memory/scoped_ptr.h"
+#include "base/win/iunknown_impl.h"
+
+namespace base {
+namespace win {
+
+// A simple implementation of IEnumVARIANT.
+class BASE_EXPORT EnumVariant
+  : public IEnumVARIANT,
+    public IUnknownImpl {
+ public:
+  // The constructor allocates an array of size |count|. Then use
+  // ItemAt to set the value of each item in the array to initialize it.
+  explicit EnumVariant(unsigned long count);
+
+  // Returns a mutable pointer to the item at position |index|.
+  VARIANT* ItemAt(unsigned long index);

[M-A Ruel, 2011/12/01 00:35:13]

Why doesn't it return a reference? Just wondering.

[dmazzoni, 2011/12/02 00:44:07]

I'm used to the Google coding style of pointers for mutable, const refs for
immutable - and in this case, I think a pointer is better since we're using
memcpy in Clone(). But it's just a slight preference.

+
+  // IUnknown.
+  ULONG STDMETHODCALLTYPE AddRef() OVERRIDE;
+  ULONG STDMETHODCALLTYPE Release() OVERRIDE;
+  STDMETHODIMP QueryInterface(REFIID riid, void** ppv) OVERRIDE;
+
+  // IEnumVARIANT.
+  STDMETHODIMP Next(ULONG requested_count,
+                    VARIANT* out_elements,
+                    ULONG* out_elements_received);
+  STDMETHODIMP Skip(ULONG skip_count);
+  STDMETHODIMP Reset();
+  STDMETHODIMP Clone(IEnumVARIANT** out_cloned_object);
+
+ private:
+  ~EnumVariant();
+
+  scoped_array<VARIANT> items_;
+  unsigned long count_;
+  unsigned long current_index_;
+};
+
+}  // namespace win
+}  // namespace base
+
+#endif  // BASE_WIN_ENUM_VARIANT_H_