Drag and Drop for macos

DragContainer.swift

import Cocoa

protocol DragContainerDelegate {
    func draggingEntered()
    func draggingExit()
    func draggingFileAccept(_ files: [URL])
}

// https://stackoverflow.com/questions/29233247/implementing-a-drag-and-drop-zone-in-swift
class DragContainer: NSView {
    var delegate: DragContainerDelegate?
    
    let acceptTypes = ["png", "jpg", "jpeg"]
    
    
    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        setup()
    }
    
    required init?(coder decoder: NSCoder) {
        super.init(coder: decoder)
        setup()
    }
    
    // https://stackoverflow.com/questions/29233247/implementing-a-drag-and-drop-zone-in-swift
    func setup(){
        registerForDraggedTypes([NSPasteboard.PasteboardType(kUTTypeTIFF as String),
                                 NSPasteboard.PasteboardType(kUTTypeURL as String)])
    }
    
        
    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)
    }
    
    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        delegate?.draggingEntered()
        let acceptFiles = checkExtension(sender)
        return acceptFiles ? NSDragOperation.generic : NSDragOperation()
    }
    
    override func draggingExited(_ sender: NSDraggingInfo?) {
        delegate?.draggingExit()
    }
    
    override func prepareForDragOperation(_ sender: NSDraggingInfo) -> Bool {
        return true
    }
    
    
    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        var files: [URL] = []
        if let board = sender.draggingPasteboard().propertyList(forType: NSPasteboard.PasteboardType(rawValue:"NSFilenamesPboardType")) as? [String] {
            for path in board {
                let url = URL(fileURLWithPath: path)
                let fileExtension = url.pathExtension.lowercased()
                if acceptTypes.contains(fileExtension){
                    files.append(url)
                }
            }
        }
        delegate?.draggingFileAccept(files)
        return true
    }
    
    // https://stackoverflow.com/questions/31657523/os-x-swift-get-file-path-using-drag-and-drop
    func checkExtension(_ draggingInfo: NSDraggingInfo) -> Bool {
        if let board = draggingInfo.draggingPasteboard().propertyList(forType: NSPasteboard.PasteboardType(rawValue:"NSFilenamesPboardType")) as? [String] {
            for path in board {
                let url = URL(fileURLWithPath: path)
                let fileExtension = url.pathExtension.lowercased()
                if acceptTypes.contains(fileExtension) {
                    return true
                }
            }
        }
        return false
    }
    
}