Change userInfo in timer selector function in Swift - swift

Question

I want to update the userInfo of the timer in the selector function every time the timer fires.
userInfo:
var timerDic = ["count": 0]
Timer:
Init: let timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("cont_read_USB:"), userInfo: timerDic, repeats: true)
selector function:
public func cont_read_USB(timer: NSTimer)
{
if var count = timer.userInfo?["count"] as? Int
{
count = count + 1
timer.userInfo["count"] = count
}
}
I get an error on the last line:
'AnyObject?' does not have a member named 'subscript'
What is wrong here?
In Objective_C this task worked with a NSMutableDictionary as userInfo

Answer 1

To make this work, declare timerDic as an NSMutableDictionary:
var timerDic:NSMutableDictionary = ["count": 0]
Then in your cont_read_USB function:
if let timerDic = timer.userInfo as? NSMutableDictionary {
if let count = timerDic["count"] as? Int {
timerDic["count"] = count + 1
}
}
Discussion:
Swift dictionaries are value types, so if you want to be able to update it you have to pass an object. By using an NSMutableDictionary you get an object type that is passed by reference, and it can be modified since it is a mutable dictionary.
Complete example for Swift 4+:
If you don't want to use an NSMutableDictionary, you can create your own class. Here is a complete example using a custom class:
import UIKit
class CustomTimerInfo {
var count = 0
}
class ViewController: UIViewController {
var myTimerInfo = CustomTimerInfo()
override func viewDidLoad() {
super.viewDidLoad()
_ = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(update), userInfo: myTimerInfo, repeats: true)
}
#objc func update(_ timer: Timer) {
guard let timerInfo = timer.userInfo as? CustomTimerInfo else { return }
timerInfo.count += 1
print(timerInfo.count)
}
}
When you run this in the simulator, the count that is printed increases every second.

Answer 2

NSTimer.userInfo is of type AnyObject so you need to cast it to your target object:
public func cont_read_USB(timer: NSTimer)
{
if var td = timer.userInfo as? Dictionary<String,Int> {
if var count = td["count"] {
count += 1
td["count"] = count
}
}
}