I am trying to find a count of entities which satisfy predicate. According to documentation and "header" files, this should work:
let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "FileRecord")
let ctx: NSManagedObjectContext = GetCtx()
let res = try ctx.count(for: fetch)
however I get compile error:
Cannot invoke 'count' with an argument list of type '(for: NSFetchRequest<NSFetchRequestResult>)'
however when I create the fetch request from FileRecord like this instead:
let fetch: NSFetchRequest<FileRecord> = FileRecord.fetchRequest()
I get the following error:
Cannot convert value of type 'NSFetchRequest<FileRecord>' to expected argument type 'NSFetchRequest<NSFetchRequestResult>'
Please anyone got an idea what can be wrong? I am a decent C++ language lawyer but I am just a novice with Swift...
EDIT: SOLVED
My example above was wrong. In reality I had code functionally identical to:
let res: UInt64 = try ctx.count(for: fetch)
since count returns Int, the function did not match. The error message was not specific enough for me to see it immediately. Thanks to all who have tried to help :)
Related
I'm new to coding and picked up some open source project to get the idea.
I'm getting the error:
Ambiguous reference to member 'subscript'
in the code below:
let pictures = ( selectedRestaurant["Pictures"] as! NSArray ) // Error
let picture = ( pictures[zoomedPhotoIndex] as! NSDictionary )
let pictureURL = picture["url"] as! String
let imageURL = NSURL(string: pictureURL)
let urlRequest = NSURLRequest(URL: imageURL!)
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue()) {
response, data, error in
if error == nil && data != nil {
self.imageView.image = UIImage(data: data!)
self.imageView.contentMode = UIViewContentMode.ScaleAspectFit
}
}
Just specify explicitly what is the type of pictures:
So instead of:
let pictures = selectedRestaurant["Pictures"] as! NSArray
Write:
let pictures: NSArray = selectedRestaurant["Pictures"] as! NSArray
For me the answer was to specifically state the type of array I was casting to:
if let foo = dictionary["bar"] as? [String]
It means that "Pictures" is not a valid subscript. It looks like you are creating a constant named pictures and you are trying to assign it a value of selectedRestaraunt["Pictures"] and then trying to cast it as an NSArray. If selectedrestaraunt is already an array, then what goes in the [] brackets after selectedRestaraunt should be an integer value which will refer to an index in the selectedRestaraunt array. Obviosuly "Pictures" is not an integer, it is a string.
If you are trying to access an array within an array. Meaning that Pictures is an array stored within the selectedRestarauntarray then you can access it by using selectedRestaraunt[index of Pictures array] where [index of pictures array] is an integer which is equal to the index number in which the Picutres array resides within the selectedRestaraunt array
I managed to get this error in a somewhat weird way. I had code like this:
cell.textLabel = anArrayOfStrings[indexPath.item].uppercased()
And I was stumped as to why it couldn't figure out that this was an array, even though I very clearly declared its type. I broke the line in two and finally got a helpful error message:
let name = anArrayOfStrings[indexPath.item].uppercased()
cell.textLabel = name
I was trying to assign a String to a UILabel, but somehow the point at which the type inference engine failed was at the subscript.
So my advice to anyone stumped by this is to try to break up your statement into bite-sized chunks that the Swift type inference engine can more easily digest.
As Eric and Eugene mentioned in their comments it is impossible to review the issue you are having without knowing the selectedRestaurant type. That is after all why you are getting the compiler ambiguity error.
I have to respectfully disagree with MikeG though. The problem is not one of a valid subscript. You'd be getting that kind of error, if for example you had a selectedRestaurant type of [NSNumber:AnyObject], where clearly String is no longer valid since the dictionary key could only be an NSNumber.
I'm trying to write a general argmin function in Swift. Here is my code:
func argmin<X, Y:Comparable, R:SequenceType, where X== R.Generator.Element>
(f:(X)->Y, domain:R)->X{
var gen = domain.generate()
var best = gen.next()!
var minval = f(best)
while let this = gen.next() {
let value = f(this)
if value < minval {
best = this
minval = value
}
}
return best
}
I get the error message "Expected identifier to name generic parameter" when I try to compile this definition. I have no idea what this means. It sounds like an error one would get on calling the function, not defining it, but even then, I wouldn't understand it.
I'm just starting to learn Swift. Can you explain this message? (BTW, I know this function will blow up if called with an empty sequence. I'm not worrying about that yet.)
You have to remove this comma:
func argmin<X, Y:Comparable, R:SequenceType, where X== R.Generator.Element>
^
Placed that, it tells the compiler there's another generic parameter. The error message just says that - maybe in a cryptic way, but once you know, it's clearer what it means
Say I have
var dict = parseJSON(getJSON(url)) // This results in an NSDictionary
Why is
let a = dict["list"]![1]! as NSDictionary
let b = a["temp"]!["min"]! as Float
allowed, and this:
let b = dict["list"]![1]!["temp"]!["min"]! as Float
results in an error:
Type 'String' does not conform to protocol 'NSCopying'
Please explain why this happens, note that I'm new to Swift and have no experience.
dict["list"]![1]! returns an object that is not known yet (AnyObject) and without the proper cast the compiler cannot know that the returned object is a dictionary
In your first example you properly cast the returned value to a dictionary and only then you can extract the value you expect.
To amend the answer from #giorashc: use explicit casting like
let b = (dict["list"]![1]! as NSDictionary)["temp"]!["min"]! as Float
But splitting it is better readable in those cases.
I've tried dozens of things to get this right and just can't come up with anything that works. Can anyone tell me what's wrong with the following Swift code:
let incomingRequest: CFHTTPMessageRef? = CFDictionaryGetValue(self.incomingRequests as CFMutableDictionaryRef, unsafeAddressOf(incomingFileHandle!)) as CFHTTPMessageRef
The code above gives the error message: 'UnsafePointer<Void>' is not convertible to 'CFHTTPMessageRef'
I guess what I don't understand is how do I convert an 'UnsafePointer' returned by a Core Foundation function to the pointer type it should be (i.e. CFHTTPMessageRef in this case). How do I find documentation on how to do this. I've read everything I can find, but nothing so far explains how to recast return values to what they should have been in the first place. This has to be documented somewhere, doesn't it?
EDIT
Here's the code I'm having trouble with:
let incomingRequest = CFDictionaryGetValue(self.incomingRequests as CFMutableDictionaryRef, unsafeAddressOf(incomingFileHandle!))
unsafeBitCast(incomingRequest, CFHTTPMessageRef.self)
if (incomingRequest != nil) {
let success: Boolean = CFHTTPMessageAppendBytes(incomingRequest as CFHTTPMessageRef, unsafeAddressOf(data!.bytes) as UnsafePointer<UInt8>, data!.length)
if success { // Do something... }
The CFHTTPMessageAppendBytes call still gives a "Type 'UnsafePointer' does not conform to protocol 'AnyObject'". And the following 'if' check for 'success' complains that "Type 'Boolean' doesn not conform to protocol 'BooleanType'". What the heck is that about? Boolean isn't a Boolean type?
I find the strict type checking of Swift extremely frustrating. So far it is far more difficult to code in than Obj-C, C, or any of the other languages I've used. I'm sure it's because I just don't get it, or haven't found the right documentation, but this is really driving me crazy.
Use unsafeBitCast. As following example:
import Foundation
var x = "1"
var dict : NSMutableDictionary = [x: "2"]
var y = CFDictionaryGetValue(dict as CFMutableDictionaryRef, unsafeAddressOf(x))
let str: NSString = unsafeBitCast(y, NSString.self)
str == "2"
FYI: There is one quora related with unsafeBitCast. http://www.quora.com/Why-does-Swift-not-allow-implicit-type-conversion
I am quite new to swift and got a pretty weird compiler error:
Command
/Applications/Xcode6-Beta5.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc
failed with exit code 254
The Error occours when I ad the following lines to my code:
var response = HoopsClient.instance().collections["posts"]
response = response["_id"]
when I remove the second line everything compiles fine. I don't get it ^^
edit: The reason is probably that "response" is of type "AnyObject" according to the compiler... but shouldn't that be detected by xcode or give me a runtime error instead of this compiler error?
Try casting response as the type you're expecting. From what you're trying to do, instance().collections I would assume that it should return some type of dictionary.
var response = HoopsClient.instance().collections["posts"] as NSDictionary
That way, response now can handle subscripts so you could now (in theory) do:
response = response["_id"]
However
The error you get is regarding bad access to an array. This makes me think that instance().collections actually returns an array of some sort, containing Post objects.
Arrays in Swift can only handle Integer subscripts. If you want to access the information of a Post in the array, you can do something like this:
for post: Post in response {
println(post._id)
}
I know this is a long shot, but hope it helps.
Swift tends to throw error when it cant infer the type of an object, what you could probably do is add a conditional cast as follows
Im assuming that HoopsClient.instance().collections["posts"] is either a Dictionary or an Array
var response = HoopsClient.instance().collections["posts"]
if response is NSArray {
let item = response.objectAtIndex(0)
let reponseId: Post = item
}
if response is NSDictionary {
let item = response.objectForKet("_id")
let reponseId: Post = item
}
Any way, in my experience you should try to cast your variables when assigning from types that return AnyObject, xcode doesn't handle very well type inferring and when it's unable to infer the type the interface starts to throw error, like text editor uncoloring the code.