UIActivityItem

There is no type named UIActivityItem, but if you ever used the UIActivityViewController to share contents, you may notice that the first parameter is called activityItems. It’s an array of Any. If the element of it has a type I think the name would be UIActivityItem.

Let’s talk about the UIActivityItem today.

Common Usage

let activityItem = URL(string: "https://www.apple.com")!
let activityItems = [activityItem]
let activityViewController = UIActivityViewController(activityItems: activityItems, applicationActivities: nil)
present(activityViewController, animated: true)

It’s simple. We also can share other things like texts, images, and files.

If the element of the activityItems is literally an Any, this post will end here. But it’s not, here is a class named UIActivityItemProvider.

UIActivityItemProvider

Like its name, this class can provide the actual item to share. The difference with set the item to activityItems directly is the timing to create the item.

To set the item to activityItems directly, we have to create the item first, with UIActivityItemProvider we can start creating the item after the user selected a destination to share.

If creating the item is a time-consuming task, this little timing change can make a big improvement for the user who opened the UIActivityViewController by mistake.

We have to make a subclass since all properties of it are get-only.

class ActivityItemProvider: UIActivityItemProvider {
    override var item: Any {
        // Create the item here
    }
}

The getter of the item will not block the main thread, so it’s better to make a progress indicator for the user. A HUD may be handy in this situation, here is a post that discuss the HUD.

And for the same reason, the user can cancel the sharing by a drag-down gesture or tapping the close button. We can check the result of the sharing this way:

activityViewController.completionWithItemsHandler = { activityType, completed, returnedItems, error in
    if !completed {
        // Dismiss the progress indicator here
    }  
}

You may already notice that we have to provide a placeholderItem to create a UIActivityItemProvider. It’s reasonable since the UIActivityViewController doesn’t know what to display in the preview header.

Preview header

However, it seems like only work properly with a URL. But we can control the content to display in the preview header by UIActivityItemSource.

UIActivityItemSource

UIActivityItemSource is the protocol that UIActivityItemProvider adopted. So we should be able to achieve what we have done by UIActivityItemProvider using UIActivityItemSource.

class ActivityItemSource: NSObject, UIActivityItemSource {
    func activityViewControllerPlaceholderItem(_ activityViewController: UIActivityViewController) -> Any {
        // Placeholder item
    }

    func activityViewController(_ activityViewController: UIActivityViewController, itemForActivityType activityType: UIActivity.ActivityType?) -> Any? {
        // Actual item
        // We even can create the item depends on the `activityType`
    }
}

However, activityViewController(_:dataTypeIdentifierForActivityType:) will block the main thread, so when we need to run a time-consuming task to create the item, we had better to subclass from UIActivityItemProvider and override the method we need instead of adopting UIActivityItemSource directly.

To customize the preview header, we have to implement an optional method:

import LinkPresentation
class ActivityItemProvider: UIActivityItemProvider {
    ...
    override func activityViewControllerLinkMetadata(_ activityViewController: UIActivityViewController) -> LPLinkMetadata? {
        let linkMetadata = LPLinkMetadata()
        linkMetadata.title = "Apple" // Title
        linkMetadata.originalURL = URL(string:"https://www.apple.com/")! // Domain
        let imageProvider = NSItemProvider(contentsOf: Bundle.main.url(forResource: "apple", withExtension: "jpg"))
        linkMetadata.imageProvider = imageProvider // Icon image
        return linkMetadata
    }
}

Since this API use LinkPresentation to display the preview header, this usage may look a little weird when we provide a non-URL item. But setting the title and the icon image should be enough in most cases.

Conclusion

Instead of always setting the activityItems for UIActivityViewController directly, let’s keep it in mind that we can use UIActivityItemProvider or UIActivityItemSource to provide a better user experience.