SwiftUI: How to drag and drop an email from Mail on macOS - macos

Question

As a follow up on #Asperi's answer of my question on how to drag and drop contacts and, I'd also like to be able to drag and drop email in the same way. Here is my code:
import SwiftUI
import UniformTypeIdentifiers
let uttypes = [String(kUTTypeEmailMessage)]
struct ContentView: View
{
let dropDelegate = EmailDropDelegate()
var body: some View
{
VStack
{
Text("Drag your email here!")
.padding(20)
}
.onDrop(of: uttypes, delegate: dropDelegate)
}
}
struct EmailDropDelegate: DropDelegate
{
func validateDrop(info: DropInfo) -> Bool
{
return true
}
func dropEntered(info: DropInfo)
{
print ("Drop Entered")
}
func performDrop(info: DropInfo) -> Bool
{
let items = info.itemProviders(for: uttypes)
for item in items
{
print (item.registeredTypeIdentifiers) // prints []
item.loadDataRepresentation(forTypeIdentifier: kUTTypeEmailMessage as String, completionHandler: { (data, error) in
if let data = data
{
print(data)
}
})
}
return true
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
I'm not getting any data back that I can decode.
2020-11-08 09:34:54.877532+0000 DropContact[3856:124769] Cannot find representation conforming to type public.email-message
This feature has been eluding me forever so any help would be very much appreciated.

Answer 1

Well... the approach is the same, the only thing is that Apple Mail does not provide kUTTypeEmailMessage UTI representation on drag (copy)
If we register self for generic kUTTypeContent UTI and investigate content of pasteboard on drop mail from Mail, we get:
Ie, here is a complete list of representations:
com.apple.mail.PasteboardTypeMessageTransfer,
com.apple.mail.PasteboardTypeAutomator,
com.apple.pasteboard.promised-file-url,
dyn.ah62d4rv4gu8y6y4usm1044pxqzb085xyqz1hk64uqm10c6xenv61a3k,
NSPromiseContentsPboardType,
com.apple.pasteboard.promised-file-content-type,
dyn.ah62d4rv4gu8yc6durvwwa3xmrvw1gkdusm1044pxqyuha2pxsvw0e55bsmwca7d3sbwu,
Apple files promise pasteboard type,
public.url,
CorePasteboardFlavorType 0x75726C20,
dyn.ah62d4rv4gu8yc6durvwwaznwmuuha2pxsvw0e55bsmwca7d3sbwu,
Apple URL pasteboard type,
public.url-name,
CorePasteboardFlavorType 0x75726C6E,
public.utf8-plain-text,
NSStringPboardType
so now you can load data of any of those types from above (except of course Apple's own privates). And, by the way, that list might (and rather will) depend on macOS version.

Answer 2

I have no solution for this but might be on a path to it.
As I mentioned in a comment, it looks to me that SwiftUI does not have a way to fulfil file promises yet.
Afaik Mail, Photos and Safari using file promises while dragging images or mails.
This might help some one else with a solution.
func performDrop(info: DropInfo) -> Bool {
let pasteboard = NSPasteboard(name: .drag)
guard let items = pasteboard.pasteboardItems else { return false }
// it returns the content of the public.url → is an encoded message url
print(pasteboard.readObjects(forClasses: [NSURL.self]))
// getting available types for pasteboard
let types = NSFilePromiseReceiver.readableDraggedTypes.map { NSPasteboard.PasteboardType($0) }
for type in types {
for item in items {
print("type:", type)
print(item.data(forType: type))
}
}
}
This prints this:
Optional([message:%3Cf6304df5.BAAAA6Ge1-UAAAAAAAAAALTyTrMAAVNI2qYAAAAAAAcXzQBjqtkK#mailjet.com%3E])
type: NSPasteboardType(_rawValue: com.apple.NSFilePromiseItemMetaData)
nil
type: NSPasteboardType(_rawValue: dyn.ah62d4rv4gu8yc6durvwwa3xmrvw1gkdusm1044pxqyuha2pxsvw0e55bsmwca7d3sbwu)
nil
type: NSPasteboardType(_rawValue: com.apple.pasteboard.promised-file-content-type)
Optional(20 bytes)
But I don't know what data type com.apple.pasteboard.promised-file-content-type is … Maybe some kind of NSFilePromiseReceiver.
Maybe this helps someone.
Edit
Tried something else, maybe something more promising.
func performDrop(info: DropInfo) -> Bool {
let pasteboard = NSPasteboard(name: .drag)
guard let filePromises = pasteboard.readObjects(forClasses: [NSFilePromiseReceiver.self], options: nil) else { return false }
guard let receiver = filePromises.first as? NSFilePromiseReceiver else { return false }
let queue = OperationQueue.main
receiver.receivePromisedFiles(atDestination: URL.temporaryDirectory, operationQueue: queue) { (url, error) in
print(url, error)
}
}
In this example I'm able to get the NSFilePromiseReceiver but something is off.
After around 20 to 30s the callback is called and I get the URL finally – so there is maybe some potential to improve. I think it has something todo with the Queue.
Edit
I was able to move/copy the dropped mail into the download folder.
func performDrop(info: DropInfo) -> Bool {
let pasteboard = NSPasteboard(name: .drag)
guard let filePromises = pasteboard.readObjects(forClasses: [NSFilePromiseReceiver.self], options: nil) else { return false }
guard let receiver = filePromises.first as? NSFilePromiseReceiver else { return false }
let dispatchGroup = DispatchGroup()
let queue = OperationQueue()
let destUrl = URL.downloadsDirectory
dispatchGroup.enter()
var urls: [URL] = []
receiver.receivePromisedFiles(atDestination: destUrl, operationQueue: queue) { (url, error) in
if let error = error {
print(error)
} else {
urls.append(url)
}
print(receiver.fileNames, receiver.fileTypes)
dispatchGroup.leave()
}
dispatchGroup.notify(queue: .main, execute: {
print(urls)
})
}