Consider the following code:
let nsdate: NSDate? = NSDate()
if let date = nsdate as? Date { // a warning occurs here
print(date)
}
The compiler complains like this: Conditional downcast from 'NSDate?' to 'Date' is a bridging conversion; did you mean to use 'as'?
A cast from NSData to Data has the same problem. How to fix the it?
Try to cast to an optional Date:
if let date = nsdate as Date?
You're trying to optional cast of optional NSDate to NON optional Date. As long as NSDate is bridged from obj-c to Date, so this cast always success, so no optional cast required here, just basic cast as is enough. Then you need to cast optional value, so the resulting value has to be optional too, therefore Date? is appropriate here.
Swift 3.1 distinguishes
An optional down cast as? Foo
It casts a more unspecific to a more specific type for example
let dict : [String:Any] = ["Foo" : 12]
let number = dict["Foo"] as? Int
A bridge cast of an optional type as Foo?
It bridges a (Core)Foundation type to a toll free Swift type and vice versa.
It's the optional equivalent of the usual non-optional syntax
let string : NSString = "Foo"
let swiftString = string as String
The difference is subtle for the developer but very useful for the compiler.
Basically don't use the NS... Foundation classes in Swift 3 if there is a native Swift counterpart.
Try this:
let nsdate: NSDate? = NSDate()
if let date = nsdate {
print(date)
}
The compiler knows it´s an NSDate if unwrapped, so what you are doing is actually casting an NSDate to a Date
Related
I have tried
self.adc_role_id = String(res["adc_role_id"])
self.adc_role_id = "\(res["adc_role_id']"
self.adc_role_id = (\(res["adc_role_id"] as? String)!
but still get
Could not cast value of type '__NSCFNumber' to 'NSString'
I added the dump of res[4] below
As new as I am to Swift, I don't know anything else to try
In Swift 4, the String initializer requires the describing: argument label.
I don't know if this will solve your problem, but your first line of code should be written:
self.adc_role_id = String(describing: res["adc_role_id"])
In your screenshot we can see that res["adc_role_id"] is an NSNumber.
To transform an NSNumber to a String you should use its stringValue property.
And since a dictionary gives an Optional, you should use optional binding to safely unwrap it.
Example:
if let val = res["adc_role_id"] {
self.adc_role_id = val.stringValue
}
You could also, if you want, use string interpolation instead of the property:
if let val = res["adc_role_id"] {
self.adc_role_id = "\(val)"
}
but I think using the property is more relevant.
If for some reason the compiler complains about the type of the content, cast it:
if let val = res["adc_role_id"] as? NSNumber {
self.adc_role_id = val.stringValue
}
Note that you should not use String(describing:) because this initializer will try to represent the string in many ways, and some of them will give inaccurate and unexpected results (for example, if String(describing:) resolves to use the debugDescription property, as explained in the documentation, you may get a totally different string than the one you want).
It's also worth noting that using String(describing:) with an optional value such as your dictionary will resolve to a wrong string: String(describing: res["adc_role_id"]) will give Optional(yourNumber)! This is why Mike's answer is wrong. Be careful about this. My advice is to avoid using String(describing:) altogether unless for debugging purposes.
The error message is clear and the dump is clear, too.
The value is not a String, it's an Int(64) wrapped in NSNumber
Optional bind the value directly to Int (NSNumber is implicit bridged to Int) and use the String initializer.
if let roleID = res["adc_role_id"] as? Int {
self.adc_role_id = String(roleID)
}
Please conform to the naming convention that variable names are camelCased rather than snake_cased
I'm trying to create a timeStamp for sent/received messages to store inside of my database (firebase) and I'm not sure if I'm going about it correctly. Here's the line of code thats giving me an error:
Previously, I would write:
let timeStamp: NSNumber = Int(NSDate().timeIntervalSince1970))
but I'm getting the same error:
"Argument labels '(_:)' do not match any available overloads"
You can't assign an Int value to an NSNumber variable. You need to create an NSNumber from the Int. And you need to specify the parameter label:
let timeStamp: NSNumber = NSNumber(value: Int(NSDate().timeIntervalSince1970)))
Of course you now don't need to specifically state the data type:
let timeStamp = NSNumber(value: Int(NSDate().timeIntervalSince1970)))
timestamp: NSDate().timeIntervalSince1970 as NSNumber
Is it possible to change an NSDate object so that the result is equivalent to NSCalendar.startOfDayForDate(date:)? That method is only available to iOS 8 and newer, but I am looking for something that works on iOS 7.
I have looked at two methods:
NSCalendar.dateFromComponents(comps:) as described here: NSDate beginning of day and end of day. For instance, like this:
class func startOfDay(date: NSDate, calendar: NSCalendar) -> NSDate {
if #available(iOS 8, *) {
return calendar.startOfDayForDate(date)
} else {
let dateComponents = calendar.components([.Year, .Month, .Day], fromDate: date)
return calendar.dateFromComponents(dateComponents)!
}
}
NSDateFormatter.dateFromString(string:) by way of
stringFromDate(date:), i.e. converting the NSDate object into a string without the time, then converting it back into an NSDate object.
The problem with both methods is that they return an optional NSDate. I am reluctant to unwrap this implicitly and I’d rather avoid changing the return type of the method within which these methods are called.
I think the calendar.components() method returns an optional, because you can theoretically enter components that do not create valid date, like 2000-02-30. If, as in your case, the components already come from a valid date, I would not be reluctant to implicitly unwrap the optional.
I have an object from the server that is recognized by Swift 2.1 as either NSDate or NSNull. I want to put it into a struct with a property of type NSDate.
Is that possible? If not, how should I handle this to be type safe later when I use it?
struct Data {
var completedAt: [NSDate]
var name: [String]
var gender: [Bool]
}
but sometimes completedAt comes from the server as NSNull:
completedAt = "<null>";
Any help is very much appreciated, thank you.
Based on my interpretation of the text in the question you didn't mean to declare the variables as arrays.
This is how I handle my parson and I think it works pretty neatly.
The date formatter should probable not be initiated in every iteration of the constructor. If you won't use the date regularly you might want to keep the detesting until you need to parse the date or you can have a static date formatter utility that you only instantiate once.
struct Data {
var completedAt: NSDate?
var name: String
var gender: Bool
init?(dictionary: [String:AnyObject]) {
//Guessing that you want some of the values non optional...
guard let name = dictionary["name"] as? String,
let gender = dictionary["gender"] as? String
else {
return nil
}
self.name = name
self.gender = gender
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
//safe handle of optional values
if let completedAtString = dictionary["completedAt"] as? String, completedAt = dateFormater.dateFromString(completedAtString) {
self.completedAt = completedAt
}
}
}
Take a step back. For each item that the server might provide, there is no guarantee whatsoever that you receive what you expect, since you cannot control the server. So you need to decide how to react to which input.
In the case of expecting a date for example (if your data comes in JSON, that means you likely expect a string formatted in a certain way), the actual data that you receive might be an array, dictionary, string, number, bool, null, or nothing. You might then for example decide that you want to interpret nothing or null or an empty string as nil, that you want to interpret a string containing a well-formatted date as an NSDate, and anything else a fatal error in a debug version, and as either nothing or a fatal error in a release version. On the other hand, if an NSDate is absolutely required then you might interpret anything that doesn't give an NSDate as an error.
Then you write a function that delivers exactly what you want and use it. That way you can parse complex data, with your code warning you when something isn't as it should be, and with your code either surviving any possible input, or deliberately crashing on wrong input, as you want it.
this is somewhat related to this question: How to properly store timestamp (ms since 1970)
Is there a way to typeCast a AnyObject to Int64? I am receiving a huge number via JSON this number arrives at my class as "AnyObject" - how can I cast it to Int64 - xcode just says its not possible.
JSON numbers are NSNumber, so you'll want to go through there.
import Foundation
var json:AnyObject = NSNumber(longLong: 1234567890123456789)
var num = json as? NSNumber
var result = num?.longLongValue
Note that result is Int64?, since you don't know that this conversion will be successful.
You can cast from a AnyObject to an Int with the as type cast operator, but to downcast into different numeric types you need to use the target type's initializer.
var o:AnyObject = 1
var n:Int = o as Int
var u:Int64 = Int64(n)
Try SwiftJSON which is a better way to deal with JSON data in Swift
let json = SwiftJSON.JSON(data: dataFromServer)
if let number = json["number"].longLong {
//do what you want
} else {
//print the error message if you like
println(json["number"])
}
As #Rob Napier's answer says, you are dealing with NSNumber. If you're sure you have a valid one, you can do this to get an Int64
(json["key"] as! NSNumber).longLongValue