Question

It’s generally a common question.

I wonder how do mail apps implement functionality of email-receiving?
I need to implement a simple sync between two devices(for example) using my web service.

Imagine a to do list app.

Is it possible to implement such a functionality: device1 makes an entry,then sends a message to webservice, webservice informs device2 that changes took place and device2 adjusts its data and displays that entry?

Answer 1

Basically there are 2 ways:

1. polling, each device asks the webserver for changes every N minutes: new todo, delete a todo, change a todo, … and then each device will adjust. The frequency of the poll depends of the level of real time you are looking for. It can be 1 call every second or every 12 hours or much more.
2. implement a kind of BOSH protocol: the device opens a connection to the server. The server keeps it open until there something new to send to the device or the connection times out. In that case, the device reopens it.

Option 1 is better for your todo app because you don’t need real-time accuracy. The option 2 is better for a chat application where you don’t want to wait for the message.