# PHAssetImageProgressHandler The signature for a block that Photos calls while downloading asset data from iCloud. Used by the [`progressHandler`](/documentation/Photos/PHImageRequestOptions/progressHandler) property. ``` typealias PHAssetImageProgressHandler = (Double, (any Error)?, UnsafeMutablePointer, [AnyHashable : Any]?) -> Void ``` ## Discussion If you request an image whose data is not on the local device, and you have enabled downloading with the [`isNetworkAccessAllowed`](/documentation/Photos/PHImageRequestOptions/isNetworkAccessAllowed) property, Photos calls your block periodically to report progress and to allow you to cancel the download. > Note: > Photos calls this block in an arbitrary serial queue. Dispatch to the main thread if your handler needs to update the user interface. The block takes the following parameters: - progress: A floating-point value indicating the progress of the download. A value of `0.0` indicates that the download has just started, and a value of `1.0` indicates the download is complete. - error: An `NSError` object describing an error that occurred when attempting to download the image, or `nil` if no errors have occurred. - stop: A pointer to a Boolean value. To cancel the download, set `*stop` to `true` inside the block. - info: A dictionary providing additional information about the status of the image request. See Image Result Info Keys for possible keys and values. For example, a `true` value for the key [`PHImageResultIsDegradedKey`](/documentation/Photos/PHImageResultIsDegradedKey) indicates that Photos may send the full-quality version of the image later, depending on the value of the image request’s [`deliveryMode`](/documentation/Photos/PHImageRequestOptions/deliveryMode) property. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)