NSFileManager watch directory - iphone

Question

How would you monitor a directory with NSFileManager?
I would like to able to detect when a file is deleted/added in my documents directory while my app is running.

Answer 1

Here's my own version of DirectoryWatcher written in Swift using GCD instead of Mach and using a closure instead of a delegate
import Foundation
#objc public class DirectoryWatcher : NSObject {
override public init() {
super.init()
}
deinit {
stop()
}
public typealias Callback = (_ directoryWatcher: DirectoryWatcher) -> Void
#objc public convenience init(withPath path: String, callback: #escaping Callback) {
self.init()
if !watch(path: path, callback: callback) {
assert(false)
}
}
private var dirFD : Int32 = -1 {
didSet {
if oldValue != -1 {
close(oldValue)
}
}
}
private var dispatchSource : DispatchSourceFileSystemObject?
#objc public func watch(path: String, callback: #escaping Callback) -> Bool {
// Open the directory
dirFD = open(path, O_EVTONLY)
if dirFD < 0 {
return false
}
// Create and configure a DispatchSource to monitor it
let dispatchSource = DispatchSource.makeFileSystemObjectSource(fileDescriptor: dirFD, eventMask: .write, queue: DispatchQueue.main)
dispatchSource.setEventHandler {[unowned self] in
callback(self)
}
dispatchSource.setCancelHandler {[unowned self] in
self.dirFD = -1
}
self.dispatchSource = dispatchSource
// Start monitoring
dispatchSource.resume()
// Success
return true
}
#objc public func stop() {
// Leave if not monitoring
guard let dispatchSource = dispatchSource else {
return
}
// Don't listen to more events
dispatchSource.setEventHandler(handler: nil)
// Cancel the source (this will also close the directory)
dispatchSource.cancel()
self.dispatchSource = nil
}
}
Use it like Apple's DirectoryWatcher example, something like this:
let directoryWatcher = DirectoryWatcher(withPath: "/path/to/the/folder/you/want/to/monitor/", callback: {
print("the folder changed")
})
Destroying the object will stop watching, or you can stop it explicitly
directoryWatcher.stop()
It should be compatible with Objective C they way it's written (untested). Using it would be like this:
DirectoryWatcher *directoryWatcher = [DirectoryWatcher.alloc initWithPath: #"/path/to/the/folder/you/want/to/monitor/" callback: ^(DirectoryWatcher *directoryWatcher) {
NSLog(#"the folder changed")
}];
Stopping it is similar
[directoryWatcher stop];

Answer 2

Look Kernel Queues: An Alternative to File System Events in Apple documentation.
There is an example for iOS in AVPlayerDemo (look DirectoryWatcher class).
Also, check Directory Monitor blog post.