Re-register immediately after app update

[davidvavra]

GCM registration ID is only valid for one version of the app. It's a good practice to listen to MY_PACKAGE_REPLACED Broadcast receiver and re-register immediately after the update. Otherwise GCM messages will not come until user launches to app.

[adrien-aubel]

+1!

[DanielNovak]

+1 on this. I will try to make a pull request. Here is some background on this https://medium.com/@murki/gcm-push-notifications-registration-done-right-7aba759d1d55.
The registration can change after updating the app and in that case the GCM messages will stop to work until the user starts the app again. I do think that this is a rare case and the registration ID does not change after updating in normal cases - but this needs to be addressed anyway.

[DanielNovak]

I have made a proof-of-concept commit. I need to finish some details - the most important one is to prevent starting the GCM registration process if it's already running. This can happen if you update the application and start it right after updating. You will get the MY_PACKAGE_REPLACED broadcast and the first activity will start the registration too. I think I will go with a singleton for the GCMHelper so that I can track the registration state (or I will just use a static attribute).
ETA: 24 hours

[davidvavra]

@DanielNovak Great work, thanks! I posted about your library and it's spreading on G+ like a virus :) Can you also merge pull requests or @martinadamek has to do it? There is enough of them for a new version.

[DanielNovak]

I can do it, I just pinged @martinadamek so he can take a quick look. I am not sure about #8 - this a controversial change, so I don't know if we will add this into the next release :-). The rest will be merged and a new version released as soon as possible.

[martinadamek]

Yes, let's put as much as possible into new release.