Adds a class that makes it easy to subclass a HWND and filter messages sent to it.

ui/base/win/hwnd_subclass_unittest.cc

+// Copyright (c) 2012 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.
+
+#include "base/basictypes.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "ui/base/win/window_impl.h"
+#include "ui/base/win/hwnd_subclass.h"
+
+namespace ui {
+
+typedef testing::Test HWNDSubclassTest;
+
+namespace {
+
+class TestWindow : public ui::WindowImpl {
+ public:
+  TestWindow() : saw_message(false) {}
+  virtual ~TestWindow() {}
+
+  bool saw_message;
+
+ private:
+   // Overridden from ui::WindowImpl:
+  virtual BOOL ProcessWindowMessage(HWND window,
+                                    UINT message,
+                                    WPARAM w_param,
+                                    LPARAM l_param,
+                                    LRESULT& result,
+                                    DWORD msg_map_id) OVERRIDE {
+    if (message == WM_NCHITTEST)
+      saw_message = true;
+
+    return FALSE;  // Results in DefWindowProc().
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(TestWindow);
+};
+
+class TestMessageFilter : public HWNDMessageFilter {
+ public:
+  TestMessageFilter() : consume_messages(false), saw_message(false) {}
+  virtual ~TestMessageFilter() {}
+
+  // Setting to true causes the filter subclass to stop messages from reaching
+  // the subclassed window procedure.
+  bool consume_messages;
+
+  // True if the message filter saw the message.
+  bool saw_message;
+
+ private:
+  // Overridden from HWNDMessageFilter:
+  virtual bool FilterMessage(HWND hwnd,
+                             UINT message,
+                             WPARAM w_param,
+                             LPARAM l_param,
+                             LRESULT* l_result) OVERRIDE {
+    if (message == WM_NCHITTEST) {
+      saw_message = true;
+      return consume_messages;
+    }
+    return false;
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(TestMessageFilter);
+};
+
+}  // namespace
+
+TEST_F(HWNDSubclassTest, Filtering) {
+  TestWindow window;
+  window.Init(NULL, gfx::Rect(0, 0, 100, 100));
+  EXPECT_TRUE(window.hwnd() != NULL);
+
+  {
+    TestMessageFilter* mf = new TestMessageFilter;
+    HWNDSubclass subclass(window.hwnd());
+    subclass.SetFilter(mf);
+
+    // We are not filtering, so both the filter and the window should receive
+    // this message:
+    ::SendMessage(window.hwnd(), WM_NCHITTEST, 0, 0);
+
+    EXPECT_TRUE(mf->saw_message);
+    EXPECT_TRUE(window.saw_message);
+
+    mf->saw_message = false;
+    window.saw_message = false;
+
+    mf->consume_messages = true;
+
+    // We are now filtering, so only the filter should see this message:
+    ::SendMessage(window.hwnd(), WM_NCHITTEST, 0, 0);
+
+    EXPECT_TRUE(mf->saw_message);
+    EXPECT_FALSE(window.saw_message);
+  }
+}
+
+}  // namespace ui