Detect a Null value in NSDictionary

Question

I have an `NSDictionary` that's populated from a JSON response from an API server. Sometimes the values for a key in this dictionary are `Null` I am trying to take the given value and drop it into the detail text of a table cell for display. The problem is that when I try to coerce the value into an `NSString` I get a crash, which I think is because I'm trying to coerce `Null` into a string. What's the right way to do this? What I want to do is something like this: ``` cell.detailTextLabel.text = sensor.objectForKey( "latestValue" ) as NSString ``` Here's an example of the Dictionary: ``` Printing description of sensor: { "created_at" = "2012-10-10T22:19:50.501-07:00"; desc = ""; id = 2; "latest_value" = ""; name = "AC Vent Temp"; "sensor_type" = temp; slug = "ac-vent-temp"; "updated_at" = "2013-11-17T15:34:27.495-07:00"; } ``` If I just need to wrap all of this in a conditional, that's fine. I just haven't been able to figure out what that conditional is. Back in the Obje…

Accepted Answer

You can use the `as?` operator, which returns an optional value (`nil` if the downcast fails)

```
if let latestValue = sensor["latestValue"] as? String {
    cell.detailTextLabel.text = latestValue
}
```

I tested this example in a swift application

```
let x: AnyObject = NSNull()
if let y = x as? String {
    println("I should never be printed: \(y)")
} else {
    println("Yay")
}
```

and it correctly prints `"Yay"`, whereas

```
let x: AnyObject = "hello!"
if let y = x as? String {
    println(y)
} else {
    println("I should never be printed")
}
```

prints `"hello!"` as expected.

Detect a Null value in NSDictionary

Solution

Problem