Remote Files vs. Pasteboard

A macOS demo project to demonstrate how to put remote files on local clipboard and provide data asynchronously when pasting in Finder

How to use the Demo Project

• Build and Run using Xcode
• Provide a fake remote file name in the text field (or keep the default)
• Click "Trigger Remote File Copy"
• Open Finder
• Go to "Edit - Paste Item" or press Command+V
• The app will automatically become active again and prompt you to provide some dummy data for the remote file
• Enter some text into the text field (or keep the default)
• Notice that if you switch back to Finder after a second or two a progress dialog appeared
• This dialog will stay on screen until you click either "OK" or "Cancel" in the alert in the demo app
• To complete the paste, either click "OK" or "Cancel" in the alert in the demo app
• If you click cancel, the file will be copied to the destination anyway, but it will remain empty

How it works

Here's a basic overview of how this works:

• An empty temporary file is written to a temporary path on the file system using the provided file name
• A class implementing the NSFilePresenter protocol is passed to -[NSFileCoordinator addFilePresenter:]
• The pasteboard's contents are cleared
• The temporary file URL is written to the pasteboard
• As soon as paste is triggered in Finder, -[NSFilePresenter relinquishPresentedItemToReader:] is called
• The data is written asynchronously to the temporary file (in a real application, the data would first be downloaded, then written to disk)
• Once the write is complete, the completion handler is invoked
• The file presenter is removed from NSFileCoordinator to prevent further invocations
• This returns control of the paste operation to the system
• The temporary file is finally copied to its target location