SyncSession

The transfer direction (upload or download) tracked by a given progress notification block.

Progress notification blocks can be registered on sessions if your app wishes to be informed how many bytes have been uploaded or downloaded, for example to show progress indicator UIs.

The desired behavior of a progress notification block.

Progress notification blocks can be registered on sessions if your app wishes to be informed how many bytes have been uploaded or downloaded, for example to show progress indicator UIs.

A token corresponding to a progress notification block.

Call invalidate() on the token to stop notifications. If the notification block has already been automatically stopped, calling invalidate() does nothing. invalidate() should be called before the token is destroyed.

A struct encapsulating progress information, as well as useful helper methods.

Register a progress notification block.

If the session has already received progress information from the synchronization subsystem, the block will be called immediately. Otherwise, it will be called as soon as progress information becomes available.

Multiple blocks can be registered with the same session at once. Each block will be invoked on a side queue devoted to progress notifications.

The token returned by this method must be retained as long as progress notifications are desired, and the invalidate() method should be called on it when notifications are no longer needed and before the token is destroyed.

If no token is returned, the notification block will never be called again. There are a number of reasons this might be true. If the session has previously experienced a fatal error it will not accept progress notification blocks. If the block was configured in the forCurrentlyOutstandingWork mode but there is no additional progress to report (for example, the number of transferrable bytes and transferred bytes are equal), the block will not be called again.