downloadAttachment
Downloads the selected attachment to the "Download" folder in the public external storage directory.
If a CDN is configured on this ChatClient, the download URL and headers are transformed via CDN.imageRequest (for images) or CDN.fileRequest (for other files) before the download is enqueued.
Return
Executable async Call downloading attachment.
Parameters
context
The context used to access the DownloadManager.
attachment
The attachment to download.