I'm receiving a JSON and I want to parse it to get a value. I'm doing this
let ddd = oneJson["restaurantId"] as! Int
print("ddd = \(ddd)")
let restaurantId = oneJson["restaurantId"] as! Int64
as you see, I'm parsing the same field. Here's my JSON
"location":"location here location","restaurantId":0
The print statement works just fine, but I get an exception on oneJson["restaurantId"] as! Int64
I love this quirk in swift (NOT).
It's one of the least intuitive gotchas of the language I know of. So it turns out that when you get a Dictionary with type AnyObject, Ints, Doubles, Floats, ARE NOT stored as the Swift native types. They're stored as... surprise! NSNumber.
Which leads to a whole host of unintuitive behavior, for instance type checking AnyObjects to see whether you have a Double or an Int (it can't be done).
For the same reason, your code is failing. Change it to:
let ddd = oneJson["restaurantId"] as! Int
print("ddd = \(ddd)")
let restaurantId = (oneJson["restaurantId"] as? NSNumber)?.longLongValue
And remind yourself again and again that when it's an AnyObject you're casting from, Swift is hiding from you the fact that it does a cast from NSNumber to Swift base types, and that in truth, they're still just NSNumbers.
I would recommend, not to use Int64 (or Int32). Int will be working in most cases.
See this post about the different integers in Swift: https://stackoverflow.com/a/27440158/4687348
Yes, it's a known bug in Swift 3, which has been solved in Swift 4.
Now, you just write like this,
let n = NSNumber.init(value: 9223372036854775807) // 2^63 - 1
print(n, n as! Int64) // will print the right answer.
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.
Swift 2.2 has broken almost all my code. Even this simple string assigning to label doesn't work anymore:
cell.categoryName.text = peopleArray![indexPath.row]["Name"] as? String
The error says "Downcast from 'String?!' to 'String' only unwraps optionals, did you mean to use '!!'?"
What changes do I have to do now.
EDIT:
More Problems:
if (dict["data"]!["DataDetails"] as! NSArray).count == 0 {
}
Due to this I am getting a segmentation fault and the error shows this: warning: cast from 'String?!' to unrelated type 'NSArray' always fails
UPDATE:
I was using NSDictionaries, NSArrays in my classes that seems to cause the problem. Changing all the literals from Obj-C to swift made the code work properly.
So, I will also recommend other developers to prefer swift literals.
it seems there are some slight differences when using the swift types and the objective-c NS... types
eg
let dic:NSDictionary? = ["a":"a"]
let str:NSString? = dic!["a"] as? NSString
let dic2:Dictionary? = ["b":"b"]
let str2:String? = dic2!["b"] //dont need to do any casting, already optional
print(str)
print(str2)
prints
Optional(a)
Optional("b")
so depending on how your array / dictionary is defined, you might need different casting/unwrapping
I have this code in Swift and it works, but I would think there is a better way to get my object from NSNumber and convert it to a Double:
var rating: NSNumber
var ratingDouble: Double
rating = self.prodResult?.prodsInfo.prodList[indexPath.row].avgRating as NSNumber!!
ratingDouble = Double(rating.doubleValue)
Update
Swift's behavior here has changed quite a bit since 1.0. Not that it was that easy before, but Swift has made it harder to convert between number types because it wants you to be explicit about what to do with precision loss. Your new choices now look like this:
var rating: NSNumber
var ratingDouble: Double
ratingDouble = rating as! Double // 1
ratingDouble = Double(exactly: rating)! // 2
ratingDouble = Double(truncating: rating) // 3
ratingDouble = rating.doubleValue // 4
if let x = rating as? Double { // 5
ratingDouble = x
}
if let x = Double(exactly: rating) { // 6
ratingDouble = x
}
This calls Double._forceBridgeFromObjectiveC which calls Double(exactly:) with Double, Int64, or UInt64 based on the stored type in rating. It will fail and crash the app if the number isn't exactly representable as a Double. E.g. UInt64.max has more digits than Double can store, so it'll crash.
This is exactly the same as 1 except that it may also crash on NaN since that check isn't included.
This function always returns a Double but will lose precision in cases where 1 and 2 would crash. This literally just calls doubleValue when passing in an NSNumber.
Same as 3.
This is like 1 except that instead of crashing the app, it'll return nil and the inside of the statement won't be evaluated.
Same as 5, but like 2 will return nil if the value is NaN.
If you know your data source is dealing in doubles, 1-4 will probably all serve you about the same. 3 and 4 would be my first choices though.
Old Answer for Swift 1 and 2
There are several things you can do:
var rating: NSNumber
var ratingDouble: Double
ratingDouble = rating as Double // 1
ratingDouble = Double(rating) // 2
ratingDouble = rating.doubleValue // 3
The first item takes advantage of Objective-Cbridging which allows AnyObject and NSNumber to be cast as Double|Float|Int|UInt|Bool.
The second item presumably goes through a constructor with the signature init(_ number: NSNumber). I couldn't find it in the module or docs but passing AnyObject in generated an error that it cannot be implicitly downcast to NSNumber so it must be there and not just bridging.
The third item doesn't employ language features in the same way. It just takes advantage of the fact that doubleValue returns a Double.
One benefit of 1 is that it also works for AnyObject so your code could be:
let ratingDouble = self.prodResult!.prodsInfo.prodList[indexPath.row].avgRating! as Double
Note that I removed the ? from your function and moved the ! in. Whenever you use ! you are eschewing the safety of ? so there's no reason to do both together.