Swift: Create Class with NSTimer - swift

Question

I want to create a DirectoryWatcher class that detects whether a directory has changed its first level content and then calls a delegate. This will also run in another thread.
Here is my code:
protocol DirectoryWatcherDelegate {
func directoryDidChange(path: String)
}
class DirectoryWatcher {
private(set) var path = ""
private let timer: NSTimer
private let fm = NSFileManager.defaultManager()
private var previousContent: [String]
let delegate: DirectoryWatcherDelegate?
init(initPath: String) {
path = initPath
timer = NSTimer.scheduledTimerWithTimeInterval(10, target: self, selector: Selector("checkDir"), userInfo: nil, repeats: true)
}
func start() {
previousContent = getContentAtPath()
timer.fire()
}
func stop() {
timer.invalidate()
}
private func checkDir() {
if previousContent != getContentAtPath() {
dispatch_async(dispatch_get_main_queue(), { () -> Void in
if let delegate = self.delegate {
delegate.directoryDidChange(self.path)
} else {
print("No delegate has been assigned")
}
})
}
}
private func getContentAtPath() -> [String] {
var content: [String]
do {
content = try fm.contentsOfDirectoryAtPath(path)
} catch {
content = []
}
return content
}
}
My Problem ist in the init methode, where I initialize the NSTimer. Because this is the init methode I am not able to use self, bacause it is uninitialized.
How to fix this?
BTW: The error messages I am getting are:
The variable self.timer used before initialized
and
Return from initializer without initializing all stored properties