After learning that it's practically impossible to work with a file geodatabase (*.gdb) in Runtime, I started looking more into the Runtime geodatabase (*.geodatabase) and have found that it's not really very useful in a disconnected environment either. It seems that I can add features to a table, but these adds are only added in memory and are only persisted if the application can connect to a FeatureService to synchronize it. It also seems that there is no way to add a table to it. Is this correct?
Is there anything I can do to edit a *.geodatabase file while offline?
Support for the File Geodatabase format is only available when using the LocalServer component of the ArcGIS Runtime SDKs. This supports creation/read/write and traditional check-out/check-in replication workflows. Direct read/write from the ArcGIS Runtime itself is not currently on the roadmap.
The new Mobile geodatabase (*.geodatabase) is the main workflow for ArcGIS Runtime (and support is coming to ArcGIS Desktop/Pro too). Edits can be made to the mobile geodatabase whilst your app/device is offline but the geodatabase must have been extracted initially from a sync-enabled feature service to be able to make and save/synchronize edits. Once your app/device is back online you can synchronize any edits based on your specific workflow (bi-directional, upload-only, download-only, etc).
Do you intend to ever have a geodatabase solution available for applications which are never online and are permanently disconnected? The primary purpose of this would be for sharing map data between our systems, which are all offline.
Support for creating editable mobile geodatabases (.geodatabase) from ArcGIS Desktop / Pro is on the roadmap for a future release (and ideally a workflow for integrating those fields back into your enterprise geodatabase). Currently mobile geodatabases created as part of the Share As > ArcGIS Runtime Content dialog or Create Runtime Content GP tool are read-only.
In 10.2.X and the upcoming Quartz (100) release, editable geodatabases must originate from a service (ArcGIS Server or ArcGIS Online). But once created they can be edited offline and shared between apps if that's part of your workflow. There's the question of how these edits are integrated back into a the central database, unless that's not part of your architecture?
To edit geodatabases requires a Standard license (License your app—ArcGIS Runtime SDK for .NET | ArcGIS for Developers).