I'm trying to make an unsafeMutablePointer with a context, and I'm getting the error "No exact matches in call to initializer". Not sure what is going on here. Working off this answer.
let context = UIGraphicsGetCurrentContext()
var pixels:Any?
if let data = context?.data
{
pixels = UnsafeMutablePointer<CUnsignedChar>(data) // No exact matches in call to initializer
}
This answer was written 5 years ago, which is too old in the Swift world.
I could not find a right answer searching with No exact matches in call to initializer with UnsafeMutablePointer, but there would be many articles about pointer handling when Swift changed the way how to convert the pointee type of pointers.
Please try this one:
let context = UIGraphicsGetCurrentContext()
var pixels: UnsafeMutablePointer<CUnsignedChar>? = nil
if let data = context?.data {
pixels = data.assumingMemoryBound(to: CUnsignedChar.self) //<-
}
(You should better not use Any as far as you can.)
Related
I try to convert my code to swift 3 an I have spent hours on the following error:
Type 'Any' has no subscript members
Here's was my original code:
let data: AnyObject = user.object(forKey: "profilePicture")![0]
I looked at the answers here but I'm still stuck. (I do programming as a hobby, I'm not a pro :/)
I've try that:
let object = object.object(forKey: "profilePicture") as? NSDictionary
let data: AnyObject = object![0] as AnyObject
But now I get this error:
Variable used within its own initial value
Second issue: Use always a different variable name as the method name, basically use more descriptive names than object anyway.
First issue: Tell the compiler the type of the value for profilePicture, apparently an array.
if let profilePictures = user["profilePicture"] as? [[String:Any]], !profilePictures.isEmpty {
let data = profilePictures[0]
}
However, the array might contain Data objects, if so use
if let profilePictures = user["profilePicture"] as? [Data], !profilePictures.isEmpty {
let data = profilePictures[0]
}
Or – what the key implies – the value for profilePicture is a single object, who knows (but you ...)
And finally, as always, don't use NSArray / NSDictionary in Swift.
I have an array of float value (floatArray) coming from HDF5 file, and I'd like to use this data as an input for the function that accepts Unsafe[Mutable]Pointer (inputForFunction). I'm new to UnsafePointer, so I need someone's help.
One way I have in mind is, to store the array to a file, then to open it and to map the file descriptor to the memory of the variable for the input of the function:
// read the data from HDF5 file
var floatArray: [Float] = try originalHDF5DataSet.read()
// store the data
let dataToStore = NSData(bytes: &floatArray, length: sizeOfArray * MemoryLayout<Float>.size)
let tmpPath = URL(fileURLWithPath: NSTemporaryDirectory())
let filePath = tmpPath.appendingPathComponent("floatArrayData").appendingPathExtension("dat")
do{
try data.write(to: filePath, options: .atomic)
let fileManager : FileManager = FileManager.default
if fileManager.fileExists(atPath:filePath.path){
print("Success")
}else{
print("Fail")
}
// open the data
let dataPath = filePath.path
let fd = open(dataPath, O_RDONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)
assert(fd != -1, "Error: failed to open output file at \""+dataPath+"\" errno = \(errno)\n")
// memory map the parameters
let hdr = mmap(nil, Int(sizeOfArray), PROT_READ, MAP_FILE | MAP_SHARED, fd, 0)
// cast Void pointers to Float
let inputForFunction = UnsafePointer<Float>(hdr!.assumingMemoryBound(to: Float.self))
} catch{
print("failed")
}
However, it may not be the best implementation because the process to store the data seems time-consuming.
That's why I'm considering to use UnsafePointer to pass the pointer from floatArray to inputForFunction, but I'm not sure how to implement it. Just for your information, one way I'm thinking of is to use withUnsafePointermethod directly:
var floatArray: [Float] = try originalHDF5DataSet.read()
var inputForFunction = UnsafeMutablePointer<Float>.allocate(capacity: Int(sizeOfArray))
withUnsafePointer(to: &floatArray[0]) { (ptr: UnsafePointer<Float>) in
inputForFunction = UnsafeMutablePointer(mutating: ptr)
}
or the other way is to use withMemoryRebound (but the following didn't work):
var floatArray: [Float] = try originalHDF5DataSet.read()
var inputForFunction = UnsafeMutablePointer<Float>.allocate(capacity: Int(sizeOfArray))
withUnsafePointer(to: &floatArray) { (ptrDataArray: UnsafePointer<[Float]>) in
inputForFunction = ptrDataArray.withMemoryRebound(to: inputForFunction.self, capacity: Int(sizeOfArray), { (ptr: UnsafePointer<[Float]>) -> UnsafeMutablePointer<Float> in
return ptr[0]
})
}
My question is
How to pass the address of floatArray's data to inputForFunction?
If I need to convert from UnsafePointer<[Float]> to Unsafe[Mutable]Pointer, how to do it?
If needed, how to use withMemoryRebound for this purpose? Can I assign
the address/value to inputForFunction inside the closure?
When I checked the addresses of floatArray and floatArray[0], they were different (This seems different from C/C++). Which address should be passed to inputForFunction?
You can find many articles explaining how you can get Unsafe(Mutable)Pointer<Float> from [Float]. Some of them answer some of your questions. Try find them later.
How to pass the address of floatArray's data to inputForFunction?
You usually use the Array's methods withUnsafeBufferPointer or withUnsafeMutableBufferPointer. You can get an Unsafe(Mutable)BufferPointer<Element> inside the closure parameter, which contains an Unsafe(Mutable)Pointer<Element> as its baseAddress property.
var floatArray: [Float] = try originalHDF5DataSet.read()
floatArray.withUnsafeBufferPointer {unsafeBufferPointer in
let inputForFunction = unsafeBufferPointer.baseAddress
//`unsafeBufferPointer` (including its `baseAddress`) is valid only in this closure.
//So, do not pass `inputForFunction` outside of the closure, use it inside.
//...
}
If I need to convert from UnsafePointer<[Float]> to Unsafe[Mutable]Pointer, how to do it?
When you find something like UnsafePointer<[Float]>, then you are going the wrong way. In Swift, Array is a hidden struct which may contain (multi-level) indirect reference to its elements. You usually have no need to use UnsafePointer<Array<Float>>.
If needed, how to use withMemoryRebound for this purpose? Can I assign the address/value to inputForFunction inside the closure?
When you have an Array of AType and want to pass it as an Unsafe(Mutable)Pointer<AnotherType>, you may utilize withMemoryRebound. But in your case, you only need to work with Float, so withMemoryRebound may not be needed for your purpose.
When I checked the addresses of floatArray and floatArray[0], they were different (This seems different from C/C++). Which address should be passed to inputForFunction?
None. As I wrote above, address of floatArray is just pointing somewhere which contains a hidden struct, so it's completely useless for your purpose. And address of floatArray[0] is neither guaranteed to be the address of the first element of the whole content. Swift may create a temporal region which contains only one element, and passing the address of the temporal region.
By the way, do you really need to convert your [Float] to Unsafe(Mutable)Pointer<Float>?
If your functions' signature is something like this:
func takingUnsafePointer(_ pointer: UnsafePointer<Float>)
You can call it like:
takingUnsafePointer(floatArray)
//In this case `floatArray` can be a `let` constant.
Or else, if the function signature is:
func takingUnsafeMutablePointer(_ pointer: UnsafeMutablePointer<Float>)
Call it as:
takingUnsafeMutablePointer(&floatArray)
//In this case `floatArray` needs to be a `var`, not `let`.
Remember, in both cases, the passed pointer is valid only while the function call. You should not export the pointer somewhere else.
Array type have withUnsafeBufferPointer method.
This method accept closure with UnsafeBufferPointer which is like UnsafePointer<[Float]> you're asking for.
In you need UnsafePointer to the start of Array you can use baseAddress property of UnsafeBufferPointer.
Example code:
let bufferPointer: UnsafeBufferPointer<Float> = floatArray.withUnsafeBufferPointer { bufferPointer in
return bufferPointer
}
or
let baseAddress: UnsafePointer<Float> = floatArray.withUnsafeBufferPointer { bufferPointer in
return bufferPointer.baseAddress
}
EDIT: Or if it's function just passing &floatArray may work.
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'd like the user to input a String to access a key in the dictionary which then returns its coupled value. I'm sure this isn't the only thing wrong with my code but trying to see if I have the right idea and hoping for some additional direction:
Main two issues are writing the correct syntax to connect the user input getInput() (String) inside the function callfunc planetAndTime()The function is passing my dictionary as a parameter.
My other issue is returning my function's double value. ->Double`
func getInput() -> String{
let kb: NSFileHandle = NSFileHandle.fileHandleWithStandardInput()
let inputData: NSData = kb.availableData
let strData = NSString(data: inputData, encoding:NSUTF8StringEncoding) as! String
return strData
}
/////////
let nameOfPlanetsAndTime:[String:Double] = ["Mercury":0.00000816,
"Venus":0.00044, "Mars":0.0000239, "Jupiter":0.00062, "Saturn":0.000204,
"Uranus":0.000289, "Neptune":0.000459, "Pluto":0.000794,
"Center of the Milky Way":25000.000000, "Earth's Cousin":1400.000000]
print("Choose planet")
func planetAndTime(nameOfPlanetsAndTime: [String:Double], userLocation:String) ->Double{
let userLocation = getInput()
if (nameOfPlanetsAndTime[userLocation] < 0){
print("Not a Valid Location, Please Try Again")}
else{
nameOfPlanetsAndTime[userLocation]!
print(nameOfPlanetsAndTime)
}
}
There are a few issues with your code that are due to a misunderstanding of how the Swift language works so I would recommend going through the official Swift documentation for some good examples of the Swift features. To give you a little head start however I will choose a section of your code. For example, instead of writing"
if (nameOfPlanetsAndTime[userLocation] < 0){
print("Not a Valid Location, Please Try Again")}
you can write
guard let planet = nameofPlanetsAndTime[userLocation] {
print("Not a Valid Location, Please Try Again")
return nil
}
return planet
and change the return type of your function to an optional Double. So the method signature would look like
func planetAndTime(nameOfPlanetsAndTime: [String:Double], userLocation:String) ->Double?
Understanding optionals is super important in the Swift "world" and I highly recommend taking a good look at how to use them. I hope this little example is helpful.
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html#//apple_ref/doc/uid/TP40014097-CH5-ID309
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