Using NSSpeechStatusNumberOfCharactersLeft to update a progress indicator for NSSpeechSynthesizer - swift

Question

I'm new to Swift and OS X programming. I'm trying to use a progress monitor to indicate the progress of my speech synthesizer speaking text.
let speechSynthesizer = NSSpeechSynthesizer()
speechSynthesizer.delegate = self;
speechSynthesizer.startSpeakingString(contents)
I would like to set
progressIndicator.maxValue = Double(NSSpeechStatusNumberOfCharactersLeft.characters.count)
and then periodically update the progressIndicator with NSSpeechStatusNumberOfCharactersLeft, which according to Apple's documentation should hit 0.
Every way I try to access this key, it returns the same inaccurate number, so I'm obviously not using it correctly. The only example I found was in Objective-C
NSNumber *n = [[self.speechSynth objectForProperty:NSSpeechStatusProperty error:NULL] objectForKey:NSSpeechStatusNumberOfCharactersLeft];
and I tried to translate that to Swift, but still, no dice.
let count = try speechSynthesizer.objectForProperty(NSSpeechStatusProperty).objectForKey(NSSpeechStatusNumberOfCharactersLeft)
I've also tried
speechSynthesizer.valueForKey(NSSpeechStatusNumberOfCharactersLeft))
speechSynthesizer.valueWithName(NSSpeechStatusNumberOfCharactersLeft, inPropertyWithKey: NSSpeechStatusProperty))
which throw runtime exceptions. Any thoughts? Thanks in advance!

Answer 1

Your second attempt is pretty close to correct:
let count = try speechSynthesizer.objectForProperty(NSSpeechStatusProperty).objectForKey(NSSpeechStatusNumberOfCharactersLeft)
Without an error message (and since I don't have a Swift 2 compiler handy) I'm guessing the reason that this fails is that the return value of objectForProperty isn't known to be an dictionary, so you can't look up values in it.
Here's my quick & dirty Swift 3 playground for testing this:
import PlaygroundSupport
import Cocoa
let synth = NSSpeechSynthesizer()
synth.startSpeaking("I'm not standing still, I am lying in wait")
// quick way to test for progress without setting up an app and delegate
PlaygroundPage.current.needsIndefiniteExecution = true
let timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
let statusDict = try! synth.object(forProperty: NSSpeechStatusProperty) as! [String: Any]
print(statusDict[NSSpeechStatusNumberOfCharactersLeft])
}
(Obviously, you don't need all the timer stuff or playground business if you're running this in an app with a synthesizer delegate.)
The key bit (no pun intended) is to cast the return value of objectForProperty so that Swift knows it's a dictionary, then look up the number of characters in that dictionary.
Now, this code runs correctly, but it doesn't completely work for setting a progress bar — when the synthesizer finishes speaking, NSSpeechStatusNumberOfCharactersLeft is likely to be some nonzero value. (In that case, another status key, NSSpeechStatusOutputBusy will become false.) So your progress bar will get to not quite 100%, and you can use either the NSSpeechStatusOutputBusy key or the delegate didFinishSpeaking callback to take your bar the rest of the way, remove your progress UI, or whatever.