Add base/android/activity_status.cc

base/android/activity_status.h

+// Copyright 2013 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_ANDROID_ACTIVITY_STATUS_H_
+#define BASE_ANDROID_ACTIVITY_STATUS_H_
+
+#include <jni.h>
+
+#include "base/android/jni_android.h"
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/singleton.h"
+#include "base/observer_list_threadsafe.h"
+
+template <typename T> struct LeakySingletonTraits;

[joth, 2013/04/26 20:29:10]

is this needed?

[digit1, 2013/04/29 12:22:10]

Good catch, no it isn't, it's a remnant of a previous implementation. Removed.

+
+namespace base {
+namespace android {
+
+// Define activity state values like ACTIVITY_STATE_CREATED in a
+// way that ensures they're always the same than their Java counterpart.
+enum ActivityState {
+#define DEFINE_ACTIVITY_STATE(x,y) ACTIVITY_STATE_ ## x = y,
+#include "base/android/activity_state_list.h"
+#undef DEFINE_ACTIVITY_STATE
+};
+
+// A native helper class to listen to activity state changes from

[joth, 2013/04/26 20:29:10]

maybe helpful to spell out that these are Android "Activity" states.

also, *which* activity is this reporting? A process can host multiple
activities, or none at all.

(those comments apply to the java counterpart class too, I guess)

[digit1, 2013/04/29 12:22:10]

it's the current one (when active), since there can only be one per process.
I've updated the comments in both the Java and C++ sources.

+// any thread.
+//
+// To start listening, create a new instance, passing a callback to a
+// function that takes an ActivityState parameter. To stop listening,
+// simply delete the listener object. The implementation guarantees
+// that the callback will always be called on the same thread than

[joth, 2013/04/26 20:29:10]

nit: on the same thread _that was_ the one that created the lisener (?)

[digit1, 2013/04/29 12:22:10]

Done.

+// the one that created the listener.
+//
+// Example:
+//
+//    void OnActivityStateChange(ActivityState state) {
+//       ...
+//    }
+//
+//    // Start listening.
+//    ActivityStatus::Listener* my_listener =
+//        new ActivityStatus::Listener(base::Bind(&OnActivityStateChange));
+//
+//    ...
+//
+//    // Stop listening.
+//    delete my_listener
+//
+BASE_EXPORT class ActivityStatus {
+ public:
+  typedef base::Callback<void(ActivityState)>  StateChangeCallback;
+
+  class Listener {
+   public:
+    explicit Listener(const StateChangeCallback& callback);
+    ~Listener();
+
+   private:
+    friend class ActivityStatus;
+
+    void Notify(ActivityState state);
+
+    StateChangeCallback callback_;
+
+    DISALLOW_COPY_AND_ASSIGN(Listener);
+  };
+
+  // NOTE: The Java ActivityStatus is a singleton too.
+  static ActivityStatus* GetInstance();
+
+  // Internal use: must be public to be called from base_jni_registrar.cc
+  static bool RegisterBindings(JNIEnv* env);
+
+  // Internal use only: must be public to be called from JNI.
+  void OnActivityStateChange(ActivityState new_state);
+
+ private:
+  friend struct DefaultSingletonTraits<ActivityStatus>;
+
+  ActivityStatus();
+  ~ActivityStatus();
+
+  void RegisterListener(Listener* listener);
+  void UnregisterListener(Listener* listener);
+
+  scoped_refptr<ObserverListThreadSafe<Listener> > observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ActivityStatus);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_ACTIVITY_STATUS_H_