Options for Sharing Android App Data on Multiple Phones

I'm looking for suggestions for ways to share Android app data between phones running the same app. For example, lets say I have an app that stores a database of book reviews. If person A has a book review that person B doesn't have, what are the options for getting that information from person A's phone to person B's phone?

Currently, I'm aware of the following options:

- Upload data from person A's phone to a server, then download data from server to Person B's phone.
- Write code to have the phones sync up using bluetooth
- Write code to send SMS messages

I'm wondering if there are any more options besides these, and if there's actually a best-practice for accomplishing this?

Ideally, I want the users to simply click a button in the app to make the sharing take place, so I don't want to go down the bluetooth route because that requires the user to do a bit of setup (or assumes they already have set things up in the form of bluetooth settings).

Since the data can be of variable length and potentially large, I believe that would rule out text messaging.

As far as the server route goes, from what I understand this seems to be an ok way of doing things, but my problem is that I have no experience with having users potentially sign in to a server and then uploading data. I don't know of the cost concerns (if any), or of potential security concerns (allowing just anyone to upload data, I'm not sure if I would have to take steps to ensure someone couldn't bypass the app and upload malicious data).

So, can you guys give me suggestions and point me in the righ开发者_运维知识库t direction? Thanks.

I'm wondering if there are any more options besides these

You could try generating a QR code and scanning it on the other phone. Beyond that, I think you have it mostly covered.

and if there's actually a best-practice for accomplishing this?

That is impossible to answer in the abstract.

Keep the database server side and interface with it via a web service

I too am looking for a solution to this very problem. I'll throw it out there that a fourth, or rather extension of your first option, is to use the Cloud to Device Messaging Framework, though it still requires (as best I can tell) having your own server, though I suppose you wouldn't need to store the database server-side longer than it takes to send the message, provided you keep it under 1024b (or whatever the actual size is).

I don't believe there is a convenient way to monitor/send email in the background. If I could have my app monitor email messages looking for a key subject, then parsing the body, I could probably accomplish what I'm looking for using email as the transport.

The problem with maintaining a server, is that you probably would need to build in a subscription fee to your app to cover the costs of maintaining a server, as one time sales may not be able to cover the ongoing expense.