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/callback.h"

[gavinp, 2013/04/26 07:37:53]

Not needed. Favour "base/callback_forward.h" in headers if it is needed.

[digit1, 2013/04/26 12:32:40]

Good point, thanks. Done.

+#include "base/memory/ref_counted.h"
+#include "base/memory/singleton.h"
+#include "base/observer_list_threadsafe.h"
+
+template <typename T> struct LeakySingletonTraits;
+
+namespace base {
+namespace android {
+
+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
+// any thread. Clients should simply sub-class their own StateListener
+// which overrides the OnActivityStateChange method. To stop receiving
+// events, simply delete the StateListener instance. StateListener objects
+// can be created on any thread, and their OnActivityStateChange() method
+// will always ne called from the thread that created them.

[gavinp, 2013/04/26 07:37:53]

nit "always be called"

[digit1, 2013/04/26 12:32:40]

Done.

+//
+BASE_EXPORT class ActivityStatus {
+ public:
+  class StateListener {
+   public:
+    StateListener();
+    virtual ~StateListener();
+
+    virtual void OnActivityStateChange(ActivityState new_state) = 0;
+  };
+
+  static ActivityStatus* GetInstance();
+
+  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();

[gavinp, 2013/04/26 07:37:53]

~ActivityStatus() isn't defined anywhere. It's not instantiated either, as it's
leaky, but would it make sense to use an empty inline body? Our style guide
cautions against this, and the scoped_refptr cautions me too.

If we don't define a body for this, perhaps we should just comment on that?

[digit1, 2013/04/26 12:32:40]

Ah, I've added an empty body. I guess this won't matter in the end, the function
will be removed by the linker.

+
+  void RegisterStateListener(StateListener* state_listener);
+  void UnregisterStateListener(StateListener* state_listener);
+
+  scoped_refptr<ObserverListThreadSafe<StateListener> > observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ActivityStatus);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_ACTIVITY_STATUS_H_