Early on, we realized that we needed some way to communicate to the user when data isn’t synced with the server yet. Otherwise, you could end up in a frustrating situation where you see a card you created on your device, but no one else can see it and

Most of what I’ve written so far has been about uploading changes from the client to the server. But we found it is equally important to download changes from the server periodically, too. What use is offline mode when you aren’t viewing fresh data? How can you share

When writing offline mode, attachments proved to be a uniquely difficult aspect of syncing. The nature of attachments differ from other data in Trello. Most data in Trello are simple numbers and strings. Files are an entirely different beast; they’re large and unwieldy. File Permissions On Android, when a

I want to call out a surprisingly tricky problem we ran into when developing offline mode: handling identifiers. In Trello, all models have an ID. Each board, list, card, etc. It’s how we define relationships between models as well as how we communicate with the server about them. When

In the last article we discussed how we sync our changes with the server. Ideally, those HTTP requests would always work - if only we could walk the rosy path of best-case scenarios! Unfortunately, when it comes to network requests, all sorts of madness can occur. It’s best to

Going offline meant using our database for all immediate changes to the client. But obviously we later want to sync those changes with the server. The basic idea behind our sync is to store changes made offline as a series of deltas that are later uploaded to the server. In

Good news, everyone! The Trello mobile apps now work offline! Offline mode has been the most requested mobile feature for years. It’s frustrating to lose the ability to use Trello when you enter the subway or you’re flying on a plane. Even more importantly, using Trello in an