OS X detect new screenshot event with Swift

ScreenshotDetector.swift

import Foundation

typealias NewFileCallback = (fileURL: NSURL) -> Void

class ScreenshotDetector: NSObject, NSMetadataQueryDelegate {
    
    let query = NSMetadataQuery()
    
    var newFileCallback: NewFileCallback?

    override init() {
        super.init()
        
        let center = NSNotificationCenter.defaultCenter()
        center.addObserver(self, selector: Selector("queryUpdated:"), name: NSMetadataQueryDidStartGatheringNotification, object: query)
        center.addObserver(self, selector: Selector("queryUpdated:"), name: NSMetadataQueryDidUpdateNotification, object: query)
        center.addObserver(self, selector: Selector("queryUpdated:"), name: NSMetadataQueryDidFinishGatheringNotification, object: query)
        
        query.delegate = self
        query.predicate = NSPredicate(format: "kMDItemIsScreenCapture = 1")
        query.startQuery()
    }
    
    deinit {
        query.stopQuery()
    }
    
    func queryUpdated(notification: NSNotification) {
        if let userInfo = notification.userInfo {
            for v in userInfo.values {
                let items = v as! [NSMetadataItem]
                if items.count > 0 {
                    let item = items[0]
                    if let filename = item.valueForAttribute("kMDItemFSName") as? String {
                        let filenameWithPath = NSString(string: "~/Desktop/" + filename).stringByExpandingTildeInPath
                        let url = NSURL(fileURLWithPath: filenameWithPath, isDirectory: false)
                        if let cb = self.newFileCallback {
                            cb(fileURL: url)
                        }
                    }
                }
            }
        }
    }
}

////////////////////////////
// Usage                  //
////////////////////////////

// Because this object is observing events it should stay
// in memory for the duration of its usage.
// In a view controller for instance it should be allocated
// in the class scope. If its reference is stored inside
// a method it will be deallocated automatically when the
// method returns and consequently stop obsering any events.
let detector = ScreenshotDetector()

// The actual callback can be assigned anywhere there's
// a reference to the instance.
detector.newFileCallback = { fileURL in
  // fileURL is an NSURL instance of the screenshot file.
}

Hi,
I tried to call this class, but I made a mistake.

2020-02-09 19:00:51.389151+0100 XXX [59278:4184587] -[XXX.ScreenshotDetector queryUpdated:]: unrecognized selector sent to instance 0x600000221400
2020-02-09 19:00:51.389514+0100 XXX[59278:4184587] Failed to set (contentViewController) user defined inspected property on (NSWindow): -[XXX.ScreenshotDetector queryUpdated:]: unrecognized selector sent to instance 0x600000221400
2020-02-09 19:00:51.876467+0100 XXX[59278:4184587] -[XXX.ScreenshotDetector queryUpdated:]: unrecognized selector sent to instance 0x600000221400
2020-02-09 19:00:51.912782+0100 XXX[59278:4184587] [General] -[XXX.ScreenshotDetector queryUpdated:]: unrecognized selector sent to instance 0x600000221400
please help me

Does this require sandbox permissions? I'm not receiving any notifications.

I'm pretty sure this approach to subscribing to screenshot updates doesn't work anymore. It broke a couple of years ago and I haven't looked further into it since.

Yeah looks like if I remove sandboxing it works. Which is fine for my demo app. There might be an entitlement I can set but for now that's fine. 👍