events: Introduce PlatformEventDispatcher and PlatformEventSource.

ui/events/platform/platform_event_source.cc

+// Copyright 2014 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 "ui/events/platform/platform_event_source.h"
+
+#include <algorithm>
+
+#include "base/message_loop/message_loop.h"
+#include "ui/events/event.h"
+#include "ui/events/platform/platform_event_dispatcher.h"
+#include "ui/events/platform/platform_event_observer.h"
+#include "ui/events/platform/scoped_event_dispatcher.h"
+
+namespace ui {
+
+// static
+PlatformEventSource* PlatformEventSource::instance_ = NULL;
+
+PlatformEventSource::PlatformEventSource()
+    : overridden_dispatcher_(NULL), overridden_dispatcher_restored_(false) {

[sky, 2014/03/25 15:51:15]

nit: when you wrap one param per line.

[sadrul, 2014/03/25 18:33:15]

Done.

+  CHECK(!instance_) << "Only one platform event source can be created.";
+  instance_ = this;
+}
+
+PlatformEventSource::~PlatformEventSource() {
+  CHECK_EQ(this, instance_);
+  instance_ = NULL;
+}
+
+PlatformEventSource* PlatformEventSource::GetInstance() { return instance_; }
+
+void PlatformEventSource::AddPlatformEventDispatcher(
+    PlatformEventDispatcher* dispatcher) {
+  CHECK(dispatcher);

[sky, 2014/03/25 15:51:15]

DCHECK not already in dispatchers_?

[sadrul, 2014/03/25 18:33:15]

Done.

+  dispatchers_.push_back(dispatcher);
+}
+
+void PlatformEventSource::RemovePlatformEventDispatcher(
+    PlatformEventDispatcher* dispatcher) {
+  PlatformEventDispatcherList::iterator remove =
+      std::remove(dispatchers_.begin(), dispatchers_.end(), dispatcher);
+  if (remove != dispatchers_.end())
+    dispatchers_.erase(remove);
+}
+
+scoped_ptr<ScopedEventDispatcher> PlatformEventSource::OverrideDispatcher(
+    PlatformEventDispatcher* dispatcher) {
+  CHECK(dispatcher);
+  overridden_dispatcher_restored_ = false;
+  return make_scoped_ptr(
+      new ScopedEventDispatcher(&overridden_dispatcher_, dispatcher));
+}
+
+void PlatformEventSource::AddPlatformEventObserver(
+    PlatformEventObserver* observer) {
+  CHECK(observer);
+  observers_.AddObserver(observer);
+}
+
+void PlatformEventSource::RemovePlatformEventObserver(
+    PlatformEventObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+uint32_t PlatformEventSource::DispatchEvent(PlatformEvent platform_event) {
+  uint32_t action = POST_DISPATCH_PERFORM_DEFAULT;
+  bool should_quit = false;
+
+  if (!WillProcessEvent(platform_event)) {
+    // Give the overridden dispatcher a chance to dispatch the event first.
+    if (overridden_dispatcher_)
+      action = overridden_dispatcher_->DispatchEvent(platform_event);
+    should_quit = !!(action & POST_DISPATCH_QUIT_LOOP);
+
+    if (action & POST_DISPATCH_PERFORM_DEFAULT) {
+      for (PlatformEventDispatcherList::iterator i = dispatchers_.begin();
+           i != dispatchers_.end();
+           ++i) {
+        PlatformEventDispatcher* dispatcher = *(i);
+        if (dispatcher->CanDispatchEvent(platform_event))
+          action = dispatcher->DispatchEvent(platform_event);
+        if (action & POST_DISPATCH_QUIT_LOOP)
+          should_quit = true;
+        if (action & POST_DISPATCH_STOP_PROPAGATION)
+          break;
+      }
+    }
+  }
+  DidProcessEvent(platform_event);
+  if (should_quit || overridden_dispatcher_restored_) {

[sky, 2014/03/25 15:51:15]

Why does overridden_dispatcher_restored_ == true mean you need to quit the
current loop? OverrideDispatcher doesn't spawn a nested message loop. Maybe
you're assuming each override corresponds to a nested message loop? If so, can
you document that.

[sadrul, 2014/03/25 18:33:15]

Yeah. This code was a bit misleading. I have clarified here with comments and
rearranged the code a little to make it clearer.

We should not terminate the message-loop if the override dispatcher is
destroyed. But it is necessary to stop dispatching the events from the
event-source in the current iteration of the message-loop, so that if there was
a nested message-loop active that has been terminated, it gets a chance to
unwind before events are dispatched again.

+    base::MessageLoop::current()->QuitNow();
+    action |= POST_DISPATCH_QUIT_LOOP;
+  }
+  overridden_dispatcher_restored_ = false;
+
+  return action;
+}
+
+bool PlatformEventSource::WillProcessEvent(PlatformEvent event) {
+  if (observers_.might_have_observers()) {
+    ObserverListBase<PlatformEventObserver>::Iterator it(observers_);
+    PlatformEventObserver* obs;
+    while ((obs = it.GetNext()) != NULL) {
+      if (obs->WillProcessEvent(event))
+        return true;
+    }
+  }
+  return false;
+}
+
+void PlatformEventSource::DidProcessEvent(PlatformEvent event) {
+  FOR_EACH_OBSERVER(PlatformEventObserver, observers_, DidProcessEvent(event));
+}
+
+void PlatformEventSource::OnOverriddenDispatcherRestored() {
+  CHECK(overridden_dispatcher_);
+  overridden_dispatcher_restored_ = true;
+}
+
+}  // namespace ui