Implementing a drag-and-drop zone in Swift

Question

I recently started using Swift to build OS X apps and I am wondering how I could implement a drag-and-drop zone.

More specifically, I built an app that processes ima

Answer 1

Here's an example I'm using in an application.

1. Add conformance to NSDraggingDestination to your subclass declaration if necessary (not needed for NSImageView because it already conforms to the protocol)
2. Declare an array of accepted types (at least NSFilenamesPboardType)
3. Register these types with registerForDraggedTypes
4. Override draggingEntered, draggingUpdated and performDragOperation
5. Return an NSDragOperation from these methods
6. Get the file(s) path(s) from the draggingPasteboard array

In my example I've added a function to check if the file extension is amongst the ones we want.

Swift 2

class MyImageView: NSImageView {

    override func drawRect(dirtyRect: NSRect) {
        super.drawRect(dirtyRect)
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        // Declare and register an array of accepted types
        registerForDraggedTypes([NSFilenamesPboardType, NSURLPboardType, NSPasteboardTypeTIFF])
    }

    let fileTypes = ["jpg", "jpeg", "bmp", "png", "gif"]
    var fileTypeIsOk = false
    var droppedFilePath: String?

    override func draggingEntered(sender: NSDraggingInfo) -> NSDragOperation {
        if checkExtension(sender) {
           fileTypeIsOk = true
           return .Copy
        } else {
           fileTypeIsOk = false
           return .None
        }
    }

    override func draggingUpdated(sender: NSDraggingInfo) -> NSDragOperation {
        if fileTypeIsOk {
            return .Copy
        } else {
            return .None
        }
    }

    override func performDragOperation(sender: NSDraggingInfo) -> Bool {
        if let board = sender.draggingPasteboard().propertyListForType("NSFilenamesPboardType") as? NSArray,
            imagePath = board[0] as? String {
            // THIS IS WERE YOU GET THE PATH FOR THE DROPPED FILE
            droppedFilePath = imagePath
            return true
        }
        return false
    }

    func checkExtension(drag: NSDraggingInfo) -> Bool {
        if let board = drag.draggingPasteboard().propertyListForType("NSFilenamesPboardType") as? NSArray,
            path = board[0] as? String {
            let url = NSURL(fileURLWithPath: path)
            if let fileExtension = url.pathExtension?.lowercaseString {
                return fileTypes.contains(fileExtension)
            }
        }
        return false
    }
}

Swift 3

class MyImageView: NSImageView {

    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        // Declare and register an array of accepted types
        register(forDraggedTypes: [NSFilenamesPboardType, NSURLPboardType, NSPasteboardTypeTIFF])
    }

    let fileTypes = ["jpg", "jpeg", "bmp", "png", "gif"]
    var fileTypeIsOk = false
    var droppedFilePath: String?

    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        if checkExtension(drag: sender) {
            fileTypeIsOk = true
            return .copy
        } else {
            fileTypeIsOk = false
            return []
        }
    }

    override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation {
        if fileTypeIsOk {
            return .copy
        } else {
            return []
        }
    }

    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        if let board = sender.draggingPasteboard().propertyList(forType: "NSFilenamesPboardType") as? NSArray,
            imagePath = board[0] as? String {
            // THIS IS WERE YOU GET THE PATH FOR THE DROPPED FILE
            droppedFilePath = imagePath
            return true
        }
        return false
    }

    func checkExtension(drag: NSDraggingInfo) -> Bool {
        if let board = drag.draggingPasteboard().propertyList(forType: "NSFilenamesPboardType") as? NSArray,
            path = board[0] as? String {
            let url = NSURL(fileURLWithPath: path)
            if let fileExtension = url.pathExtension?.lowercased() {
                return fileTypes.contains(fileExtension)
            }
        }
        return false
    }
}