Currently Gaia use observer event to notify Gecko to change audio volume level. But there is no API to read audio volume back for verification.

Gaia uses settings API to change and observe audio volume settings, doesn't it? Why do you need some new API to read audio volume back?

Gaia listened audio volume event from observer service for making sure this event was already sent out to Gecko (settings.js). But this only indicated setting API really sent event to notify Gecko for changing volume. It didn't reflect that Gecko actually do the right thing on volume changing. Ex: Even Gecko received volume changing event but it didn't do anything. Then Gaia still get this same event and update it's current volume too. So we need a mechanism to synchronizely get volume level from Gecko.

(In reply to Vicamo Yang [:vicamo][:vyang] from comment #7) > Take data connection settings for example. The Settings app set per APN > config values through Settings API. The RadioInterfaceLayer sees the change > and performs corresponding actions. If any failure found, > RadioInterfaceLayer resets the value through Settings API again and keeps > the settings values and the reality synced. > Your example is a right thing in true. But it seems to be some trouble on volume setting. For example 1. User pressed volume up button from level 1 to level 5 continuously. 2. During level 3 there is an error on Audio Manager then it set level back to 2 via setting API. 3. Before sound manager is noticed about this error via observer event, it continue to set audio level to 4 and 5 and we can't guarantee the observer event for error will be received on which point. This will cause the non-synchronization between sound manager (Gaia) and audio manager (gecko). So I would suggest this API to synchronization, then it just can be used to verify "volume adjusting" action. Thanks and welcome for any discussion.

Firefox OS is not being worked on