init(propertiesOfMetadataItem:valueLoadingHandler:)

Creates a metadata item whose value loads on an on-demand basis only.

Declaration

init(propertiesOfMetadataItem metadataItem: AVMetadataItem, valueLoadingHandler handler: @escaping  @Sendable (AVMetadataItemValueRequest) -> Void)

Parameters

metadataItem:
The metadata item that provides the Identifier, Extendedlanguagetag, and other property values that you want the newly created metadata item to share. The system ignores the value of this template metadata item.
handler:
A callback the system invokes to load the value for the metadata item.

Return Value

A newly created instance of AVMetadataItem.

Discussion

Use this method to create metadata items for optional display purposes. For example, a metadata item that provides a large image, should only load the image when the system requests it.

When you load the value of a metadata item you created with this initializer, the closure you provide as the value loading handler executes on an arbitrary dispatch queue, off the main thread. The handler can perform I/O and other necessary operations to obtain the value. If loading of the value succeeds, provide the value by calling respond(value:). If loading of the value fails, provide an instance an error object that describes the failure by calling respond(error:).

// A template metadata item that provides supporting data.
let templateItem = AVMetadataItem()
let artworkItem = AVMetadataItem(propertiesOf: templateItem) { request in
    if let image = UIImage(named: "large_artwork"), let data = image.pngData() {
        request.respond(value: NSData(data: data))
    } else {
        request.respond(error: AppError.imageLoadingError)
    }
}