iPhone OS's Document Sharing lets apps share files

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If you own an iPad and have installed one of several productivity apps, you might have noticed a new (and much welcome) feature: the ability to pass a file from one app to the other. For example, when you receive a Pages document in your e-mail inbox, tapping and holding its icon will result in a popover that asks you if you just want to Quick View the file or open it in Pages (assuming, of course, that you have a copy of the latter installed on your iPad).

This is the result of a new feature, called “Document Support” that Apple has quietly sneaked into version 3.2 of iPhone OS, which—at least right now—only runs on the iPad.

Document Support allows an app to “register” itself as the designated handler for a particular file type. Any app can then use the same functionality to discover whether another app can handle a file and pass the latter on to it.

While the functionality itself is nothing new—any modern operating system is capable of doing the same—it does have some significant implications for a platform like iPhone OS, where apps typically live in their own “sandbox” and can take advantage of few—and very limited—ways to talk to each other. Document Support allows inter-app communication while giving the app that “owns” of a file complete control over whether it can be transferred elsewhere on your device—you can think of it as a filesystem where files are “pushed” from one app to the other, rather than “pulled” by any app that wants to use them.

The main advantage of Document Support is that it finally allows apps to access data beyond their own boundaries without compromising the safety of the sandbox model in a significant way. Several iPad apps are already taking advantage of this feature, starting with Apple's own iWork suite. Because the functionality is publicly available to all developers, you can expect it to make its way into more and more applications: already, apps like ReaddleDocs and GoodReader offer the ability to open documents they support from compatible apps, such as Mail.

What about Quick Look?

The power of Document Support currently extends to Quick Look only in a very limited fashion. If, for example, you tap on an iWork document in Mail or Safari, a modal panel will slide up and present a quick view of the document, with the opportunity to open the file in the appropriate iWork product.

Unfortunately, the same doesn't work with non-Apple apps, because the Quick Look functionality is currently a “private” API that is not yet available to developers outside the Cupertino umbrella.

There is, however, good news on the horizon: Apple has announced that Quick Look will be available to all developers in iPhone OS 4.0, which should be available to iPad users this fall.

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