triggering an event simultaneously on multiple iOS

问题:

I would like to trigger an event (e.g. play music) on multiple iOS devices at the exact same time (by means of milliseconds)

My approach is to keep a socket connection and send a timestamp to iOS devices (10 seconds later from current time) and trigger the event on iOS devices at that timestamp.

Problem is iOS devices might differ 1 or 2 seconds and that would cause a desynchronize. And even timestamps are pointing out the same time on each devices (AFAIK) they are not on millisecond sensivity.

Is there any way to trigger an event simultaneously on multiple devices, or an approach which should be followed?

回答1:

Don't send the data over the Internet. You can't assume the connection latency will be low enough for your needs. Use Bluetooth instead. You can do with with GameKit, with dns-sd, or with a library like HHServices.

Pick a device that will act as the controller. Apple provide sample code to do so with GameKit, but it's not difficult to think up your own method. When you want to trigger the action, that controller will send a packet over Bluetooth to the other devices.

I doubt you need lower latency than that, but if you do, have the controller send packets to each connected device to ascertain the latency for each connection, have them send their timestamps to the controller, then the controller should be able to calculate a timestamp for each of them that will occur at the same time.