I'm getting this error when trying to compile this code. Can someone help me debug?:
Cannot convert value of type '(NSError!) throws -> Void' to expected
argument type '((NSError!) -> Void)!'
Header:
#class MSBTile;
#protocol MSBTileManagerProtocol <NSObject>
- (void)addTile:(MSBTile *)tile completionHandler:(void(^)(NSError *error))completionHandler;
#end
ViewController:
client.tileManager.addTile(tile, completionHandler: {
(error: NSError!) -> Void in
if error == nil || MSBErrorType(rawValue: error.code) == MSBErrorType.TileAlreadyExist {
self.output("Creating page...")
...
})
} else {
self.output(error.localizedDescription)
}
})
I found a workaround for anyone who encounters this in the future. It turns out that two of the function calls were also throwables, so I had to wrap them in try catch blocks like so:
let pageTextBlock: AnyObject
do {
pageTextBlock = try MSBPageTextBlockData(elementId: 10, text: "TextButton Sample")
}catch _ {
pageTextBlock = ""
}
let pageButtonBlock: AnyObject
do {
pageButtonBlock = try MSBPageTextButtonData(elementId: 11, text: "Press Me")
}catch _ {
pageButtonBlock = ""
}
Disclaimer: I'm still new to Swift so this may not be the best solution.
Related
I'm working with swift 5 and I get the following error for the code below "Initializer for conditional binding must have Optional type, not 'AdviceArticle'".
I saw a few similar issues dating back a few years but I cannot really translate the answers to my specific case.
static func loadAdviceArticle(articleID: String, completion: #escaping((AdviceArticle?) -> Void)) {
Firestore.firestore().collection("advice_articles").document(articleID).getDocument { (snapshot, error) in
if error != nil {
return
}
if let obj = try? snapshot?.data(as: AdviceArticle.self),
let article = obj {
completion(article)
}
}
}
Would you have a suggestion on how to fixe this code ?
Many thanks for your help.
try this:
guard let obj = try? snapshot?.data(as: AdviceArticle.self) else { return }
I got confused error handling in swift3. I try to do like "if XX function got error then try YY function"
Let me show you what I try:
class MyClass {
enum error: Error
{
case nilString
}
func findURL() {
do {
let opt = try HTTP.GET(url_adr!)
opt.start { response in
if let err = response.error {
print("error: \(err.localizedDescription)")
return //also notify app of failure as needed
}
do
{
/* This is func1. and got error. I want to if this function has error then go next function. */
try self.stringOperation(data: response.description)
}
catch{
print("doesn't work on func1. trying 2nd func")
self.stringOperation2(data:response.descritption)
}
}
} catch let error {
print("got an error creating the request: \(error)")
}
}
func stringOperation(data:String)throws -> Bool{
do{
/** 1 **/
if let _:String = try! data.substring(from: data.index(of: "var sources2")!){
print("its done")
}else{
throw error.nilString
}
IN 1: I got this fatal error on this line:
"fatal error: unexpectedly found nil while unwrapping an Optional value" and program crashed.
I googled error handling try to understand and apply to in my code. However not succeed yet. Can someone explain where did I wrong?
Additional info: I got String extension for .substring(from:...) , and .index(of:"str"). So these lines doesn't got you confused.
As a general rule, try avoiding using force unwrapping (!), where you have
if let _: String= try! data.substring...
Instead use
if let index = data.index(of: "var sources2"),
let _: String = try? data.substring(from: index) { ... } else { ... }
That way you remove the two force unwraps that may be causing your crash. You already have the if let protection for catching the nil value, so you can make the most of it by using the conditional unwrapping.
So on a button press I'm creating splitLat: [Double] from a throwing function called splitLatitude that takes currentLocation: CLLocationCoordinate2D?. I then want to use splitLat as a Label (its going to be used for other things as well but this serves the example)
#IBAction func ButtonPress() {
let splitLat = try self.splitLatitude(self.currentLocation)
LatSplitLabel.text = "\(splitLat)"
}
this gets a error "Errors thrown from here are not handled"
I resolve this by putting it in a do catch block
do{
let splitLat = try self.splitLatitude(self.currentLocation)
} catch {
print("error") //Example - Fix
}
but the when i try to set the label later on splitLat is an "unresolved identifier"
New to swift and programming in general, am i missing something basic/ do i have a mis understanding? is there a way i can use the constant from the do {} statement outside of the do statement. Tried return but that is reserved for functions.
Really appreciate any help
Thanks
You have two options (I'll assume that splitLat is String type)
do{
let splitLat = try self.splitLatitude(self.currentLocation)
//do rest of the code here
} catch {
print("error") //Example - Fix
}
second option, predeclare the variable
let splitLat : String? //you can late init let vars from swift 1.2
do{
splitLat = try self.splitLatitude(self.currentLocation)
} catch {
print("error") //Example - Fix
}
//Here splitLat is recognized
Now, some explanation of your problem.
in Swift (and many other languages) variables are only defined inside the scope they are defined
scope is defined between these brackets {/* scope code */ }
{
var x : Int
{
//Here x is defined, it is inside the parent scope
var y : Int
}
//Here Y is not defined, it is outside it's scope
}
//here X is outside the scope, undefined
A 3rd option is to use a closure:
let splitLat:String = {
do {
return try self.splitLatitude(self.currentLocation)
}
catch {
print("error") //Example - Fix
return ""
}
}()
LatSplitLabel.text = "\(splitLat)"
This is a scoping error if you want to succeed execution after the do/catch block. You must declare the variable outside of this do/catch scope in order to utilize it after the do/catch execution.
Try this:
var splitLat: <initialType> = <initialValue>
do {
let splitLat = try self.splitLatitude(self.currentLocation)
} catch {
print("error")
}
print(splitLat)
Here is a concocted example that runs in a Swift 2.2 playground:
enum Errors: ErrorType {
case SomeBadError
}
func getResult(param: String) throws -> Bool {
if param == "" {
throw Errors.SomeBadError
}
return true
}
var result = false
do {
result = try getResult("it")
} catch {
print("Some error")
}
print(result)
I am New for Swift and I Have Implement File Manager Concept in my Project but it shows the issue and I don't for how to solve this please any body help me for fix the issue.
Here I Post My Code.
class func addSkipBackupAttributeToItemAtPath(filePathString: String) throws -> Bool
{
let URL: NSURL = NSURL.fileURLWithPath(filePathString)
assert(NSFileManager.defaultManager().fileExistsAtPath(URL.path!))
let err: NSError? = nil
let success: Bool = try URL.setResourceValue(Int(true), forKey: NSURLIsExcludedFromBackupKey) //---- This Line Shows the Issue.
if !success {
NSLog("Error excluding %# from backup %#", URL.lastPathComponent!, err!)
}
return success
}
The benefit of the new error handling in Swift 2 is the omission of the quasi-redundant return values Bool / NSError. Therefore setResourceValue does not return a Bool anymore which is the reason of the error message.
As the function is marked as throws I recommend this syntax which just passes the result of setResourceValue
class func addSkipBackupAttributeToItemAtPath(filePathString: String) throws
{
let url = NSURL.fileURLWithPath(filePathString)
assert(NSFileManager.defaultManager().fileExistsAtPath(URL.path!))
try url.setResourceValue(true, forKey: NSURLIsExcludedFromBackupKey)
}
Handle the error in the method which calls addSkipBackupAttributeToItemAtPath
The method setResourceValue is a throw function and does not return a Bool.
Try running your function using a do-catch:
do {
try URL.setResourceValue(Int(true), forKey: NSURLIsExcludedFromBackupKey)
}
catch {
NSLog("Error excluding %# from backup %#", URL.lastPathComponent!, err!)
}
I would like to make a perform request function in swift using Generics. I want to make the call and switch on my enum Result based on what I get back. However, I don't understand the : 'cannot invoke performRequest with an argument list of type (NSURLRequest, (Result<__>) -> ())' Why can't I have an unnamed parameter here? I have also tried something like the following : r<MyStruct> --- but I then get an expected expression error. Any help explaining the above Result<_> error would be greatly appreciated. Thanks.
enum Result<A> {
case Value
case Error
}
func performRequest<A>(request:NSURLRequest, callback:(Result<A>) -> ()) {
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error) -> Void in
callback(parseResponse(data, response: response, error: error))
}
task.resume()
}
class SampleClass {
let request = NSURLRequest(URL: NSURL(string: "www.google.com")!)
init() {
performRequest(request) { r in -------- errors out
switch r {
case .Value:
case .Error:
}
}
}
The problem is that when you use performRequest, you have not given the compiler enough information about the generic parameter you intend to use. The critical part that is missing is that parseResponse needs to return a Result that is parameterised in the same way as the callback. However, in the snippet you provided, parseResponse is not generic.
I believe this will do what you intend. In this scenario, I've parameterised the Result with String, but you can substitute any other type.
// multi-purpose (generic) Result type
enum Result<A>
{
case Value(A) // because you parameterised the enum, you might as well take advantage of the type
case Error
}
// this is a custom parser, you may substitute your own that returns a different type
func parseString( data:NSData?, response:NSURLResponse?, error:NSError? ) -> Result<String> {
if let _ = error {
return Result.Error
}
return Result.Value("Success")
}
// this function is completely generic, but the parser and callback need to be compatible
func performRequest<A>( request:NSURLRequest,
parser:( NSData?, NSURLResponse?, NSError? ) -> Result<A>,
callback:( Result<A> ) -> Void ) {
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
( data, response, error ) -> Void in
callback( parser( data, response, error ) )
}
task.resume()
}
let request = NSURLRequest(URL: NSURL(string: "www.google.com")!)
// actual invocation, now I need to pass in a concrete parser and callback with a specific type
performRequest( request, parser: parseString ) { // parseString returns a Result<String>
r in
switch r {
case .Value( let value ):
// because I passed in a parser that returns a Result<String>, I know that "value" is a String here
print( "Succeeded with value: \(value)" )
break;
case .Error:
print( "an error occurred" )
break;
}
}