NSImageView with drag and drop capabilities written in Swift.

DragAndDropImageView.swift

//
// DragAndDropImageView.swift
// Iconizer
// https://github.com/raphaelhanneken/iconizer
//
import Cocoa

class DragDropImageView: NSImageView, NSDraggingSource {

    /// Holds the last mouse down event, to track the drag distance.
    var mouseDownEvent: NSEvent?

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)

        // Assure editable is set to true, to enable drop capabilities.
        isEditable = true
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)

        // Assure editable is set to true, to enable drop capabilities.
        isEditable = true
    }

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

    // MARK: - NSDraggingSource
    // Since we only want to copy/delete the current image we register ourselfes
    // for .Copy and .Delete operations.
    func draggingSession(_: NSDraggingSession,
                         sourceOperationMaskFor _: NSDraggingContext) -> NSDragOperation {
        return NSDragOperation.copy.union(.delete)
    }

    // Clear the ImageView on delete operation; e.g. the image gets
    // dropped on the trash can in the dock.
    func draggingSession(_: NSDraggingSession, endedAt _: NSPoint,
                         operation: NSDragOperation) {
        if operation == .delete {
            image = nil
        }
    }

    // Track mouse down events and safe the to the poperty.
    override func mouseDown(with theEvent: NSEvent) {
        mouseDownEvent = theEvent
    }

    // Track mouse dragged events to handle dragging sessions.
    override func mouseDragged(with event: NSEvent) {

        // Calculate the dragging distance...
        let mouseDown = mouseDownEvent!.locationInWindow
        let dragPoint = event.locationInWindow
        let dragDistance = hypot(mouseDown.x - dragPoint.x, mouseDown.y - dragPoint.y)

        // Cancel the dragging session in case of an accidental drag.
        if dragDistance < 3 {
            return
        }

        guard let image = self.image else {
            return
        }

        // Do some math to properly resize the given image.
        let size = NSSize(width: log10(image.size.width) * 30, height: log10(image.size.height) * 30)

        if let draggingImage = image.resize(toSize: size, aspectMode: .fit) {

            // Create a new NSDraggingItem with the image as content.
            let draggingItem = NSDraggingItem(pasteboardWriter: image)

            // Calculate the mouseDown location from the window's coordinate system to the
            // ImageView's coordinate system, to use it as origin for the dragging frame.
            let draggingFrameOrigin = convert(mouseDown, from: nil)
            // Build the dragging frame and offset it by half the image size on each axis
            // to center the mouse cursor within the dragging frame.
            let draggingFrame = NSRect(origin: draggingFrameOrigin, size: draggingImage.size)
                .offsetBy(dx: -draggingImage.size.width / 2, dy: -draggingImage.size.height / 2)

            // Assign the dragging frame to the draggingFrame property of our dragging item.
            draggingItem.draggingFrame = draggingFrame

            // Provide the components of the dragging image.
            draggingItem.imageComponentsProvider = {
                let component = NSDraggingImageComponent(key: NSDraggingItem.ImageComponentKey.icon)

                component.contents = image
                component.frame = NSRect(origin: NSPoint(), size: draggingFrame.size)
                return [component]
            }

            // Begin actual dragging session. Woohow!
            beginDraggingSession(with: [draggingItem], event: mouseDownEvent!, source: self)
        }
    }
}

Thanks for the fantastic Swift code!

On line 100:
Replace rectByOffsetting with offsetBy to make compatible with Swift 2.0.

Also this requires copyWithSize from, https://gist.github.com/behoernchen/cb924aa280f4b9dbb480

Thanks! I'm glad, someone could use this.

Apple could use it… 😂

Line 66

Value of type 'NSImage' has no member 'resize'

Apple's documentation (https://developer.apple.com/documentation/appkit/nsimage) confirms this. Has this been tested with Swift 3 / 4?

Line 66

Value of type 'NSImage' has no member 'resize'

Apple's documentation (https://developer.apple.com/documentation/appkit/nsimage) confirms this. Has this been tested with Swift 3 / 4?

@DesWurstes
I'am using this NSImageExtension, to resize the image.