A class which performs polling to determine the newly copied url of desired kind in an external app

PasteboardWatcher.swift

//
//  PasteboardWatcher.swift
//  PasteboardWatcher
//
//  Created by Devarshi Kulshreshtha on 6/19/15.PasteboardWatcher
//  Copyright © 2015 Devarshi Kulshreshtha. All rights reserved.
//

import Cocoa

/// Protocol defining the methods which delegate has/ can implement
protocol PasteboardWatcherDelegate {
    
    /// the method which is invoked on delegate when a new url of desired kind is copied
    /// - Parameter copiedUrl: the newly copied url of desired kind
    func newlyCopiedUrlObtained(copiedUrl copiedUrl : NSURL)
}

/// Use this class to notify a delegate once a url with specified kind is copied
/// - Credit goes to: **Josh Goebel**
/// - His wonderful pastie: [PasteboardWatcher in objective-c](http://pastie.org/1129293)
class PasteboardWatcher : NSObject {
    
    // assigning a pasteboard object
    private let pasteboard = NSPasteboard.generalPasteboard()
    
    // to keep track of count of objects currently copied
    // also helps in determining if a new object is copied
    private var changeCount : Int
    
    // used to perform polling to identify if url with desired kind is copied
    private var timer: NSTimer?
    
    // the delegate which will be notified when desired link is copied
    var delegate: PasteboardWatcherDelegate?
    
    // the kinds of files for which if url is copied the delegate is notified
    private let fileKinds : [String]
    
    /// initializer which should be used to initialize object of this class
    /// - Parameter fileKinds: an array containing the desired file kinds
    init(fileKinds: [String]) {
        // assigning current pasteboard changeCount so that it can be compared later to identify changes
        changeCount = pasteboard.changeCount
        
        // assigning passed desired file kinds to respective instance variable
        self.fileKinds = fileKinds
        
        super.init()
    }
    /// starts polling to identify if url with desired kind is copied
    /// - Note: uses an NSTimer for polling
    func startPolling () {
        // setup and start of timer
        timer = NSTimer.scheduledTimerWithTimeInterval(2, target: self, selector: Selector("checkForChangesInPasteboard"), userInfo: nil, repeats: true)
    }
    
    /// method invoked continuously by timer
    /// - Note: To keep this method as private I referred this answer at stackoverflow - [Swift - NSTimer does not invoke a private func as selector](http://stackoverflow.com/a/30947182/217586)
    @objc private func checkForChangesInPasteboard() {
        // check if there is any new item copied
        // also check if kind of copied item is string
        if let copiedString = pasteboard.stringForType(NSPasteboardTypeString) where pasteboard.changeCount != changeCount {
            
            // obtain url from copied link if its path extension is one of the desired extensions
            if let fileUrl = NSURL(string: copiedString) where self.fileKinds.contains(fileUrl.pathExtension!){
                
                // invoke appropriate method on delegate
                self.delegate?.newlyCopiedUrlObtained(copiedUrl: fileUrl)
            }
            
            // assign new change count to instance variable for later comparison
            changeCount = pasteboard.changeCount
        }
    }
}

Thanks for sharing. Any idea why there's nothing equivalent to UIPasteboardChangedNotification in AppKit?

how this work?? Please explain

Thanks for sharing. Any idea why there's nothing equivalent to UIPasteboardChangedNotification in AppKit?

@billibala My apologies for delayed response. Seems like it is now available as part of Mac Catalyst 13.0+, here is the link: UIPasteboardChangedNotification

how this work?? Please explain

@Gk19011994 I believe that comments added to the code explains all. In summary it performs data polling to check the changeCount on pasteboard object.