There needs to be a document describing the differences of NSExtensionItem, NSItemProvider and the items from an NSItemProvider

Number:rdar://30184485 Date Originated:25-Jan-2017 12:18 PM
Status:Open Resolved:
Product:Documentation Product Version:10.2
Classification:UI/Usability Reproducible:Always
When dealing with share or action extensions, there is a documentation missing that explains the overall picture. It is very confusing. What Xcode generates, and what the documentation says, is that an `NSExtensionContext` can have multiple input items. It does not explain how these represent the users intent of sharing one or multiple things.

For example the Photos app only hands over a single `NSExtensionItem` with multiple `NSItemProvider`, one for each image that was shared. So it seems that the `NSItemProvider` represent the users intent of sharing items and each provider represents one thing the user actually wanted to share.

Safari on the other hand hands over two `NSExtensionItem` if the user wants to share a single image. Each of them having one `NSItemProvider`. One of them contains the image and one the URL. So it seems that `NSExtensionItem` are used to represent the same data in a different way. But if this is true, there also is an item provider’s `hasItemConformingToTypeIdentifier:` and the corresponding `loadItemForTypeIdentifier:` which can be used to transform data between different representations.

So at first it seems that NSExtensionItem and `loadItemForTypeIdentifier:` serve the same purpose. However I am sure there is another reason for this. The problem is, with the lack of documentation on this, it is very hard to understand how to pick which items to process.


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