Hello!
I've had trouble with getting a blank google maps in my application and found a temporarily solution "Generate Google Maps API key without entering SHA1 code", and that works. But I don't like this approach at all, even though if it's just for development.
I haven't found any other solutions other than "You need to install Google Play Service, or make sure it's Map API v2" and such but that didn't really help me. Anyways, I've found a solution that helped me. I read somewhere in a forum where a guy told the OP to read the Output log and I did found something very interesting. Apparently upon debugging, Visual Studio is generating a debug.keystore and uses it for the project.
This means that if you created your own keystore and entered the SHA1 code to generate Google Map API Key, it won't work in development (I've only had this problem with Google Maps API). Therefore, you need to get the SHA1 code from the debug.keystore. Note that the debug.keystore does not have a password, so when asked in cmd, just press enter.
Remember to change back to your own keystore's SHA1 in your Google Maps API key.
I hope this solved the problem for any of you who experience the same issue.
Peace.