Swift Int不能转换为DictionaryIndex吗？

Question

I'm trying to convert this piece of ojb-c code:

MPMovieFinishReason finishReason = [notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey] integerValue];

to swift, and as such I have this:

var finishReason: MPMovieFinishReason = notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey.integerValue];

However this gives me the error in the title. What am I doing wrong here?

Answer 1

You have a few problems, first of all in your direct translation:

var finishReason: MPMovieFinishReason = notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey.integerValue];

The ] is in the wrong place, so you're trying to call integerValue on MPMoviePlayer... instead of on the dictionary lookup.

var finishReason: MPMovieFinishReason = notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey].integerValue;

This is still failing because userInfo is an NSDictionary and not a Dictionary, so it gets mapped to [AnyObject:AnyObject] It seems like the automatic morphing is failing you, so it's falling back to a CFString which isn't mappable to AnyObject.

The process becomes a little clearer if we break it up more:

// Recover the original dictionary, and cast is by input and output, to it
//  all makes sense.  This will allow String as a parameter and return an NSNumber
//  as a result.
let userInfo = notification.userInfo as [String:NSNumber]

// From the userInfo, let's extract the raw NSNumber using lookup
let reason = userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey]

// Convert the NSNumber into an MPMovieFinishReason enum.  Note that it's 
// 0215 and I'm on ambien so I don't care about the force unwrapping that
// should be optional unwrapping
let finishReason = MPMovieFinishReason.fromRaw(reason!.integerValue)

Many problems can be broken down into much simpler problems if you just take it a single step at a time. Modern compilers aren't even too bothered by it as the can recognize when variables are no longer in use and do proper reclamation. Also note using let instead of var for those temporary values since they shouldn't be reused anyway.

Answer 2

Try the type-casting function Int()

ie.,

var finishReason = Int(notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey]) as MPMovieFinishReason;