Refactor ActivityStatus to not store current activity

base/android/application_status_listener.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_APPLICATION_STATUS_LISTENER_H_
+#define BASE_ANDROID_APPLICATION_STATUS_LISTENER_H_
+
+#include <jni.h>
+
+#include "base/android/jni_android.h"
+#include "base/base_export.h"
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/singleton.h"
+#include "base/observer_list_threadsafe.h"
+
+namespace base {
+namespace android {
+
+// Define application state values like APPLICATION_STATE_VISIBLE in a
+// way that ensures they're always the same than their Java counterpart.
+enum ApplicationState {
+#define DEFINE_APPLICATION_STATE(x, y) APPLICATION_STATE_##x = y,
+#include "base/android/application_state_list.h"
+#undef DEFINE_APPLICATION_STATE
+};
+
+// A native helper class to listen to state changes of the Android
+// Application. This mirrors org.chromium.base.ApplicationStatus.
+// any thread.
+//
+// To start listening, create a new instance, passing a callback to a
+// function that takes an ApplicationState parameter. To stop listening,
+// simply delete the listener object. The implementation guarantees
+// that the callback will always be called on the thread that created
+// the listener.
+//
+// Example:
+//
+//    void OnApplicationStateChange(ApplicationState state) {
+//       ...
+//    }
+//
+//    // Start listening.
+//    ApplicationStatusListener* my_listener =
+//        new ApplicationStatusListener(
+//            base::Bind(&OnApplicationStateChange));
+//
+//    ...
+//
+//    // Stop listening.
+//    delete my_listener
+//
+class BASE_EXPORT ApplicationStatusListener {
+ public:
+  typedef base::Callback<void(ApplicationState)> ApplicationStateChangeCallback;
+
+  explicit ApplicationStatusListener(
+      const ApplicationStateChangeCallback& callback);
+  ~ApplicationStatusListener();
+
+  // 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 and unit tests.
+  static void NotifyApplicationStateChange(ApplicationState state);
+
+ private:
+  void Notify(ApplicationState state);
+
+  ApplicationStateChangeCallback callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(ApplicationStatusListener);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_APPLICATION_STATUS_LISTENER_H_