content/public/renderer/platform_event_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 #ifndef CONTENT_PUBLIC_RENDERER_PLATFORM_EVENT_OBSERVER_H_
   6 #define CONTENT_PUBLIC_RENDERER_PLATFORM_EVENT_OBSERVER_H_
   7
   8 #include "base/logging.h"
   9 #include "content/public/renderer/render_process_observer.h"
  10 #include "content/public/renderer/render_thread.h"
  11
  12 namespace blink {
  13 class WebPlatformEventListener;
  14 }
  15
  16 namespace content {
  17
  18 // This class is used as a base class for PlatformEventObserver<ListenerType> to
  19 // allow storing PlatformEventObserver<> with different typename in the same
  20 // place.
  21 class PlatformEventObserverBase {
  22  public:
  23   virtual ~PlatformEventObserverBase() { }
  24
  25   // Methods that need to be exposed in PlatformEventObserverBase. Their purpose
  26   // is described in PlatformEventObserver<>.
  27
  28   virtual void Start(blink::WebPlatformEventListener* listener) = 0;
  29   virtual void Stop() = 0;
  30
  31   // Helper method that allows an sub-class to write its own test helper.
  32   // The |data| type MUST be known from the caller.
  33   virtual void SendFakeDataForTesting(void* data) { }
  34 };
  35
  36 // PlatformEventObserver<> defines the basic skeleton for an object requesting
  37 // the browser process to start/stop listening to some platform/hardware events
  38 // and observe the result.
  39 // The results are received via IPC, assuming that the object was correctly
  40 // registered as an observer via the constructor taking a RenderThread.
  41 template <typename ListenerType>
  42 class PlatformEventObserver : public PlatformEventObserverBase,
  43                               public RenderProcessObserver {
  44  public:
  45   // Creates a PlatformEventObserver that doesn't listen to responses from the
  46   // browser process. Can be used for testing purposes or for observers that
  47   // have other means to get their results.
  48   PlatformEventObserver()
  49       : is_observing_(false),
  50         listener_(0) {
  51   }
  52
  53   // Creates a PlatformEventObserver that registers to the RenderThread in order
  54   // to intercept the received IPC messages (via OnControlMessageReceived). If
  55   // |thread| is null, it will not register.
  56   explicit PlatformEventObserver(RenderThread* thread)
  57       : is_observing_(false),
  58         listener_(0) {
  59     if (thread)
  60       thread->AddObserver(this);
  61   }
  62
  63   // The observer will automatically stop observing when destroyed in case it
  64   // did not stop before.
  65   virtual ~PlatformEventObserver() {
  66     if (is_observing())
  67       Stop();
  68   }
  69
  70   // Called when a new IPC message is received. Must be used to listen to the
  71   // responses from the browser process if any expected.
  72   virtual bool OnControlMessageReceived(const IPC::Message& msg) OVERRIDE {
  73     return false;
  74   }
  75
  76   // Start observing. Will request the browser process to start listening to the
  77   // events. |listener| will receive any response from the browser process.
  78   // Note: should not be called if already observing.
  79   virtual void Start(blink::WebPlatformEventListener* listener) {
  80     DCHECK(!is_observing());
  81     listener_ = static_cast<ListenerType*>(listener);
  82     is_observing_ = true;
  83
  84     SendStartMessage();
  85   }
  86
  87   // Stop observing. Will let the browser know that it doesn't need to observe
  88   // anymore.
  89   virtual void Stop() {
  90     DCHECK(is_observing());
  91     listener_ = 0;
  92     is_observing_ = false;
  93
  94     SendStopMessage();
  95   }
  96
  97  protected:
  98   // This method is expected to send an IPC to the browser process to let it
  99   // know that it should start observing.
 100   // It is expected for subclasses to override it.
 101   virtual void SendStartMessage() = 0;
 102
 103   // This method is expected to send an IPC to the browser process to let it
 104   // know that it should start observing.
 105   // It is expected for subclasses to override it.
 106   virtual void SendStopMessage() = 0;
 107
 108   bool is_observing() const {
 109     return is_observing_;
 110   }
 111
 112   ListenerType* listener() {
 113     return listener_;
 114   }
 115
 116  private:
 117   bool is_observing_;
 118   ListenerType* listener_;
 119
 120   DISALLOW_COPY_AND_ASSIGN(PlatformEventObserver);
 121 };
 122
 123 } // namespace content
 124
 125 #endif // CONTENT_PUBLIC_RENDERER_PLATFORM_EVENT_OBSERVER_H_