content/renderer/screen_orientation/screen_orientation_observer.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/public/renderer/platform_event_observer.h"
   6
   7 namespace content {
   8
   9 // ScreenOrientationObserver is a helper class implementing the
  10 // PlatformEventObserver template with blink::WebPlatformEventListener, which is
  11 // a pure virtual class because it doesn't expect listeners.
  12 // It is implemented on top of PlatformEventObserver to make sure it follows a
  13 // common code path even though it only uses part of this code path: it is not
  14 // expected to receive messages back but should send messages to start/stop
  15 // listening.
  16 // The intent of this class is to make sure that platforms that can't listen for
  17 // display rotations at a marginal cost can be told when to actually do it.
  18 class ScreenOrientationObserver
  19     : public PlatformEventObserver<blink::WebPlatformEventListener> {
  20  public:
  21   ScreenOrientationObserver();
  22   ~ScreenOrientationObserver() override;
  23
  24   // Overriding this method just to make sure |listener| is always null.
  25   void Start(blink::WebPlatformEventListener* listener) override;
  26
  27  protected:
  28   void SendStartMessage() override;
  29   void SendStopMessage() override;
  30 };
  31
  32 }; // namespace content