Uniform Type Identifier Bug on iOS — and How It Affects NetNewsWire

In NetNewsWire you can import your subscriptions from an OPML file. This is the standard way RSS readers work: you can export your subscriptions as an OPML file, and then import them into a different RSS reader.

This way you can move from reader to reader without having to redo your subscriptions list. It’s a good thing.

But in NetNewsWire for iOS (currently in beta) this sometimes doesn’t work because, for some people, the system won’t let you select an OPML file to import. (This does not happen on Macs.)

Here’s What Happens

In our app, we declare an OPML type: org.opml.opml with a file suffix .opml.

The org.opml.opml part is a Uniform Type Identifier (UTI), which is Apple’s way of defining document types.

When the user wants to import subscriptions from an OPML file, the app presents a document picker, and the app tells the picker that the user can select files of type org.opml.opml. We don’t want the user to select, for instance, a plain text file, or a Pages document, or a GIF, or whatever. We just want to make OPML files selectable. This works great — except when, for some people, it never works: it doesn’t allow them to select OPML files, and so they can’t import their subscriptions. It took a while to figure out the problem, but we did. #### Here’s the Problem We found that if a user has another app that declares an OPML UTI — and that UTI doesn’t match ours — then the document picker will not see those OPML files as the type we accept (org.opml.opml) but as something else. So far we’ve found two other definitions for OPML: com.reederapp.opmlandunofficial.opml(from Overcast). (To be clear: Reeder and Overcast are tremendous apps, and this situation is not at all their fault.) For someone with one of those apps installed, the system sees a.opmlfile suffix and decides the file is of typecom.reederapp.opmlorunofficial.opml. Which doesn’t match our type — org.opml.opml— which means the user can’t select the file. Even though the file suffix is.opml. #### One Possible Solution: Declare All the Types When presenting the document picker, we could declare that we allow com.reederapp.opmlandunofficial.opml`