Swift 2.0 Errors thrown from here are not handled

Question

Updating to 2.0 with Xcode 7 Beta 4

I have this code block

do
{
    try AVAudioSession.sharedInstance().setActive(true)
} catch let err as NSError
{
    println("Dim background error")
}

And its giving me the error (on the try line)

Errors thrown from here are not handled.

Is this a compiler error or is there something I am missing in my syntax?

I checked the docs and my code 'looks' correct.

Answer 1

What types of errors can AVAudioSession.sharedInstance().setActive(true) throw?
If it can only throw NSErrors, then there's no need of specifying this when catching the error. You could simply write:

do {
    try AVAudioSession.sharedInstance().setActive(true)
} catch {
    print("Dim background error")
}

If you want to use the error in your catch-scope, you can still access it. Swift automatically binds the thrown error to error, which can be used:

catch {
    // do something with `error`
}

If the method throws multiple types of errors, and you only want to deal with the ones that are NSErrors, you can conditionally bind them:

catch let specialError as NSError {
    // do something with `specialError`
}

You must ensure though, that every thrown error is handled. So assuming that the method can also throw a RandomError (which I just made up now), you would have to write:

catch let randomError as RandomError {
    // do something with `randomError`
}

...in addition to the catch of the NSError.
Or you could of course use the general case:

catch {
    // do something with `error`
}

---

So I assume your problem can be solved by removing let err as NSError, from your catch-statement.

Answer 2

May be a compiler bug. Anyway try removing let err as NSError ; catch alone is enough if you want to catch all errors.

Also, with Swift 2 you should use print, not println.

The following code compiles without errors with XCode 7 Beta 4:

import AVFoundation

class X {
    func y() {
        do {
            try AVAudioSession.sharedInstance().setActive(true)
        } catch {
            print("Dim background error \(error)")
        }
    }
}