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?
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.
Try the type-casting function Int()
ie.,
var finishReason = Int(notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey]) as MPMovieFinishReason;
Related
I tried for a long time to turn the text into an Int but it did not work. I tried it like this:
(AnzahlString is a textfield)
var AnzahlAInt = 0
if let AnzahlAString = AnzahlString.text {
let AnzahlAInt = Int(AnzahlAString)
}
But then I always get the error:
Value of optional type 'Int?' must be unwrapped to a value of type 'Int'
Then I added a ! at the end of Int(AnzahlAString)! so I don't get a error, but now when I press on the button, the app crashes. It was predictable, but how can I change this now to an Int without the !?
At first glance, it looks like you have two things to check for:
is AnzahlString.text present, and
does it represent an Int
The first check is in fact not necessary, since .text will never return nil, even though it's marked as Optional. This means you can safely force-unwrap it.
The second check is easily done by using the ?? operator:
let AnzahlAInt = Int(AnzahlString.text!) ?? 0
PS, just as a stylistic hint: variable names in Swift ususally start with a lowercase letter, names starting with capital letters are used for types.
PPS: your code as written shadows AnzahlAInt - the value of your var is never changed.
The reason why the resulting Int is optional, is that parsing might or might not succeed. For example, if you try to parse the string "Fluffy Bunnies" into an Int, there is no reasonable Int that can be returned, therefore the result of parsing that string will be nil.
Furthermore, if you force the parser by using !, you're telling Swift that you know for sure that the string you pass will always result in a valid Int, and when it doesn't, the app crashes.
You need to handle the situation in which the parse result is nil. For example:
if let AnzahlAIntResult = Int(AnzahlAString) {
// We only get here if the parse was successful and we have an Int.
// AnzahlAIntResult is now an Int, so it can be assigned to AnzahlAInt.
AnzahlAInt = AnzahlAIntResult
}
You did a good job so far but missed out one thing.
This line tries to convert the String into an Int. However this can fail, since your String can be something like this "dfhuse".
let AnzahlAInt = Int(AnzahlAString)
This is why the result of Int(AnzahlAString) is an Optional (Int?). To use it as an real Int, you have to unwrap it.
First solution is the !, however, every time this does fail your app crashes. Not a good Idea to use so.
The best solution would be Optional Binding, as you already used to get the text of your text field.
if let AnzahlAString = AnzahlString.text {
if let safeInt = Int(AnzahlAString) {
// You can use safeInt as a real Int
} else {
print("Converting your String to an Int failed badly!")
}
}
Hope this helps you. Feel free to ask again if something is unclear.
For unwrapping you can also use guard like this
Simple and easy
guard let AnzahlAInt = Int(AnzahlString.text!) else {
return
}
print(AnzahlAInt)
This is my first time using NSCoder and there used to be a method called encodeInteger but it seems to have vanished in Swift 3 and the docs don't seem to help.
It maybe that the confusion lies in the difference between Int and UInt64. Are they the same?
Should i be using a NSKeyedArchiver and if so how does that work to comply with NSCoding?
Here's before with the error:
And after without an error:
Why don't you use NSNumber and encode it as an object? It'd look like this:
let bigNumber: UInt64 = /* 123 */
let number = NSNumber(value: bigNumber)
// Encoding it just like a String
coder.encode(number, forKey: "BigNumberKey")
// Decoding and using the property uint64Value from NSNumber to get the UInt64 back
if let object = coder.decodeObject(forKey: "BigNumberKey") as? NSNumber {
let decodedBigNumber = object.uint64Value
}
If that's a requirement for some reason, NSCoder supports the encoding of Int64 (and you could cast it, described here).
The change from encodeInteger to just encode is part of SE-0005 (which affected a lot of different classes; UIColor.blueColor() is now UIColor.blue(), for instance).
From a server I receive a JSON string, then I try to convert it to an NSDictionary this way:
let JSON = try NSJSONSerialization.JSONObjectWithData(rToData!, options:[])
guard let JSONDictionary:NSDictionary = (JSON as! NSDictionary) else {
print("My grandma is way more NSDictionary than this")
return
}
Once converted, I try to get some data contained in the dictionary: in particular I need an array I can access this way:
let myArray = JSONDictionary["data1"][0]["data2"];
XCode really doesn't like this idea, it puts an arrow under the first bracket and says Value of optional type "AnyObject?" not unwrapped, did you mean to use "!" or "?" ?. I follow its suggestion and I insert a "!", converting my preceding code to this:
let myArray = JSONDictionary["data1"]![0]["data2"];
At this point, the following line (where I count the number of elements in data2) shows an error, stating AnyObject has no member count.
The only thing that seems to work fine is this solution but, apart from being ugly and unreadable, I really don't understand it:
let myArray = (JSONDictionary["data1"]?[0]["data2"])!;
Can you help me understand why this basic access to a key in a dictionary must be so intricate?
I must say I like Swift but I spend a lot of time dealing with optionals and bizarre XCode alerts.
There is no guarantee that your JSON dictionary will contain a value for the key data1 (OK, you know it will, but Swift doesn't) so JSONDictionary["data1"] returns an optional. You need to unwrap the optional with ? or !
Also, since you have an NSDictionary, not a Swift dictionary, Swift doesn't know the type of the values, so they are AnyObject. Now again, you know it is an array, but Swift doesn't so you get an error stating that AnyObject doesn't have a count method.
While it is more verbose, it is cleaer for both the compiler and anyone else looking at your code if you split the line into multiple lines. It also lets you downcast the various objects so that Swift knows what is going on and handle any malformed JSON;
if let array1 = JSONDictionary["data1"] as? NSArray {
if let dictionary1 = array1[0] as? NSDictionary {
if let data2Array = dictionary1["data2"] as? NSArray {
let count=data2Array.count
}
}
}
You could implement appropriate else statements to handle errors
Optionals are one of Swift's most powerful features. They help avoid a whole family of bugs associated with uninitialised variables and special sentinnel values for boundary conditions. It is important that you learn how they can help you and not just throw ? or ! at your code until it compiles.
I want to know how to create a dictionary of [String:AnyObject] from an UnsafePointer<AudioStreamBasicDescription>
I guess I don't understand how to work with an UnsafePointer<T> in Swift. Here's where I'm starting from - The AVAudioFile class has a fileFormat property which is of AVAudioFormat Type. AVAudioFormat has a streamDescription property which returns an UnsafePointer<AudioStreamBasicDescription> as a read-only property.
I'd like to see what the values are in this struct and converting to a Dictionary seems like it might be reasonable goal. In fact, there already seems to be a "settings" property on the AVAudioFormat Class that does this but I'm interested in understanding the "right way" to access the values stored in the UnsafePointer myself.
From the docs
Discussion: Returns the AudioStreamBasicDescription (ASBD) struct, for use with lower-level audio APIs
https://developer.apple.com/library/prerelease/ios/documentation/AVFoundation/Reference/AVAudioFormat_Class/index.html
Is there a way to do an unsafe conversion after checking if the struct is not nil? Would I use an unsafeBitCast here? I'm hesitant to jump into this too much as I've read that it's "extremely dangerous"...
I realize I can access the underlying memory with the following:
let audioFileURL:NSURL = NSBundle.mainBundle().URLForResource("FILENAME", with Extension: "mp3")
var file:AVAudioFile?
do {
file = try AVAudioFile(forReading: audioFileURL)
guard let file = file else {
fatalError("file must not be nil")
}
}catch {
print(error)
}
let format = file.processingFormat
let asbd:AudioStreamBasicDescription = format.streamDescription.memory
Is that dangerous and would I need to dealloc for some reason after creating the asbd constant?
I've tried to follow along with the post here http://sitepoint.com/using-legacy-c-apis-swift but I'm just not getting it... Looking for any direction on best practices here.
Update:
Doing a bit more research, it seems that it might be possible to create the dictionary using reflect based off this post: http://freecake.angelodipaolo.org/simple-reflection-in-swift/
Here's what I have so far:
let asbdMirror = reflect(asbd)
var asbdDict = [String: Any]()
for i in 0..<asbdMirror.count {
let (propertyName, childMirror) = asbdMirror[i]
asbdDict[propertyName] = childMirror.value
}
Any reason this is a bad idea?
You are doing everything correctly, you can access all the values in the description with asbd.mSampleRate and such. It wouldn't make sense to convert it to a dictionary because that's just not what it is, there are no keys for the values.
You also don't have to dealloc anything when working with pointers like this unless you allocate one yourself (when using malloc or alloc)
I am trying to unwrap a NSMutableArray from user defaults, but keep getting the error unexpectedly found nil while unwrapping an Optional value. I tried to check for nil after getting the array, but it is happening on the line that is getting the array from the UserDefaults, so I don't know how to fix this error. Can anyone help?
var classURLs: NSMutableArray = NSMutableArray();
let defaults: NSUserDefaults = NSUserDefaults(suiteName: "group.myCompany.Array")!;
classURLs = NSMutableArray(object: defaults.objectForKey("Class URLs")!);
NSUserDefaults.objectForKey returns an optional for a reason – if the key isn’t present, you get nil back. You shouldn’t just force-unwrap it with !
The most common case is this is the first time you’ve tried reading it without having ever written it.
In which case you probably want a default value, perhaps an empty array:
let classURLs = defaults.stringArrayForKey("Class URLs") as? [String] ?? []
(?? substitutes the value on the right if the value on the left is nil)
Note, it’s probably better if you’re writing Swift to go with a Swift array (e.g. [String]) rather than NSMutableArray, unless all you are going to do is pass it straight into a call to Objective-C.
You can also avoid the ! you’re using with the NSUserDefaults init by using optional chaining:
let defaults = NSUserDefaults(suiteName: "group.myCompany.Array")
var classURLs = defaults?.stringArrayForKey("Class URLs") as? [String] ?? []
If the key does not exist, the forced unwrap (!) of the nil object will result in a crash. You need to account for this case.
var classURLs = NSMutableArray(object:
NSUserDefaults.standardUserDefaults().objectForKey("foo") ?? [])
NB: transitioning from Objective-C? You don't need the semicolons! ;-)