如何使用NSNotification来检查NSTask的状态

import Foundation

class TaskObserver: NSObject {
    let task: NSTask
    
    init(launchPath: String, arguments: [String]?) {
        task = NSTask()
        task.launchPath = launchPath
        task.arguments = arguments
        super.init()
        task.delegate = self
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "taskDidTerminate:", name: NSTaskDidTerminateNotification, object: task)
    }
    
    func launch() {
        task.launch()
    }
    
    func taskDidTerminate(notification: NSNotification) {
        print("Task terminated with status \(task.terminationStatus)")
        NSNotificationCenter.defaultCenter().removeObserver(self, name: NSTaskDidTerminateNotification, object: task)
    }
}

extension TaskObserver: NSTaskDelegate {
    func taskDidTerminate(sender: NSTask) {
        print("Task did terminate")
    }
}

let taskObserver = TaskObserver(launchPath: "/usr/bin/say", arguments: ["hello"])
taskObserver.launch()