I have this function that takes care of an API call (makeAPICall) that I'd like to throw an error for certain API responses and when the httpResponse.statusCode != 200.
The problem is that, as far as I know, NSURLSession().dataTaskWithRequest(...) can't throw. Is this correct and if so, is there some workaround? Or should I do something totally different?
Since dataTaskWithRequest is an asynchronous operation, its error handling is facilitated with a completion handler. If it were to throw, it would be difficult to handle an error at the completion of the operation.
Therefore, you should handle the error condition within the completion handler. If you wanted to throw your own error upon completion, that would be possible but somewhat superfluous.
Instead of throwing an error, have your clients pass in a block, and run that block whenever the request fails (or, for that matter, when it completes successfully).
Actually you you can handle the error if occurs. For instance
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
if let error = error {
print(error)
// do whatever you want, there is an error
}
if let data = data{
print("data =\(data)")
}
if let response = response {
print("url = \(response.URL!)")
print("response = \(response)")
let httpResponse = response as! NSHTTPURLResponse
print("response code = \(httpResponse.statusCode)")
}
})
and I showed you how to get the response code as well.
Related
I have an app that makes an API call to a web server. I finally got the API call to work correctly and can now parse the JSON data the server returns, but I am stuck with trying to show an alert to the user if the request fails. For example, my server can return {"success": false, "error": "You didn't ask nicely"} Obviously that error is not real, but a representation of what can be returned. I can only check the error inside the completion block of the URLSession.shared.dataTask, but if I try to show an alert from inside that I get the error that I cannot perform any operation from a background thread on the UI.
The code is rather simple right now...
URLSession.shared.dataTask(with: self.request) { (data, response, error) in
if let error = error {
completion(.failure(error))
return
}
//continue on with processing the response...
completion(.success(fullResponse))
}.resume()
Then in my calling code I have...
connector.connect(pin) { (result) in
switch(result) {
case .success(let response):
if let response = response {
if response.success {
//do things
} else {
self.alert(title: "Error while connecting", message: response.error)
}
}
case .failure(let error):
self.alert(title: "Unable to connect", message: error)
}
}
That is causing the error that I can't do anything on the ui thread from a background thread. If that is the case, how do I let the user know that the API call failed? I have to be able to notify the user. Thank you.
You need to wrap it inside DispatchQueue.main.async as callback of URLSession.shared.dataTask occurs in a background thread
DispatchQueue.main.async {
self.alert(title: "Error while connecting", message: response.error)
}
Same also for
self.alert(title: "Unable to connect", message: error)
but it's better to wrap all code inside alert function inside the main queue to be a single place
Here's a different approach you can use, instead of calling DispatchQueue.main.async on connector.connect(pin)'s callback you could also do it before you call the completion block on your dataTask like this.
URLSession.shared.dataTask(with: self.request) { (data, response, error) in
if let error = error {
DispatchQueue.main.async {
completion(.failure(error))
}
return
}
//continue on with processing the response...
DispatchQueue.main.async {
completion(.success(fullResponse))
}
}.resume()
By doing this your code inside connector.connect(pin) won't be placed in a pyramid of doom, and everything in the completion block is running on the main thread.
connector.connect(pin) { result in
// everything in here is on the main thread now
}
I'm using swiftHTTP for requesting to my server and when my internet connection is slow, it goes to response part! I've set the example code below:
HTTP.GET("myURL") { response in
let myResponse = response.data // it comes here after the timeout
if response.statusCode == 200 {
//some code
} else {
do {
let jsonError = try JSON(data: myResponse) // in this line it goes to catch because there is no data in myresponse
} catch{
//alert for not having connection
}
}
Why does it call the response function if there's no response?
My server also says, that no request was sent.
It doesn't "go to response", it tries to make the HTTP request as expected and regardless of success or error it's completion handler is called.
The response object that is returned is an object that contains all of the information you need to determine what happened with the request.
So it will contain a timeout status code (HTTP 408), possibly an error message. If it did not respond at all, your app would not be able to handle these cases.
Say for example your user taps on their profile icon in the app and this sends a request to get the users profile, but it timed out. Do you want the user sat waiting, looking at a blank profile screen? It's much better to catch the error and handle it gracefully. In this case you could present a message to the user telling them that something went wrong and close the empty profile screen
Your response handler will also be called from swiftHTTP, if there's no or a very bad connection.To solve this problem, either check if there is an internet connection or check if the data is nil:
HTTP.GET("myURL") { response in
let myResponse = response.data // it comes here after the timeout
if response.statusCode == 200 || response.data == nil {
//some code
} else {
do {
let jsonError = try JSON(data: myResponse) // in this line it goes to catch because there is no data in myresponse
} catch{
//alert for not having connection
}
}
The important part here is the check if response.data == nil.
I'm using Alamofire with Swift kind of this way:
Alamofire.request(.GET, urlString)
.authenticate(usingCredential: credential)
.response {
(request, responseJSON, data, error) in [..and so on]
Now I wonder how I can execute some code in case the server is e.g. completely down. Something like a failed block in ObjC.
I know that I can call something like this to get an error code:
if let response = responseJSON {
var statusCode = response.statusCode
println("-->statusCode: \(statusCode)")
}
But in the case that I can't reach the server, the .response closure won't execute, so there is no error message.
How is this handled?
If you can't reach the server, you will receive a NSURLErrorDomain error via the error variable in the closure.
in my app I'm using JSON and I made a session recently so if I would like to make some http request to get data for a specific user, the user must log in before (also used by http request).
in the safari when I entering the url's of login and then the url of receive data, it does that as needed.
but in my app, I first call login and then the url for getting data, but it's probably starting a new session in every url request which leads me to get an error and not receive the data.
my url request function is:
static func urlRequest (adress: String, sessionEnded: (NSDictionary->Void)?){
println(adress)
var urli = NSURL(string: adress)
var request = NSURLRequest(URL: urli!)
var rVal = "";
self.task = NSURLSession.sharedSession().dataTaskWithURL(urli!) {(data, response, error) in
var parseError: NSError?
let parsedObject: AnyObject? = NSJSONSerialization.JSONObjectWithData(data,
options: NSJSONReadingOptions.AllowFragments,
error:&parseError)
let po = parsedObject as NSDictionary
if let a = sessionEnded{
sessionEnded!(po)
}
}
task!.resume()
}
thanks in advance!!
You have shared only half of the puzzle with us, the client code. We can't comment on why the app isn't working with a clearer picture of what the server API. For example, once you "log in", how do subsequent queries confirm that the request is coming from valid session. Furthermore, you report that "every url request which leads me to get an error". Well, what error do you receive? You have to be far more specific regarding the precise errors/crashes you are receiving. BTW, are you logging on to some service with a well-defined API or are you writing that code yourself, too?
Having said that, I might suggest a few refinements to this method:
The sessionEnded (which I've renamed completionHandler to conform to informal standard naming conventions), probably should return an optional NSError object, too, so the caller can detect if there was an error.
Your unwrapping of the sessionEnded completion handler can be simplified to use ?.
When you parse the object, you should feel free to perform the optional cast, too.
You probably want to detect a network error (in which case data would be nil) and return the network NSError object.
Minor point, but I'd probably also rename the function to conform to Cocoa naming conventions, using a verb to start the name. Perhaps something like performURLRequest.
This is your call, but I'd be inclined to have the method return the NSURLSessionTask, so that the caller could use that task object if it wanted to (e.g. save the task object so that it could cancel it later if it wanted to).
Thus, that yields something like:
func performURLRequest (address: String, completionHandler: ((NSDictionary!, NSError!) -> Void)?) -> NSURLSessionTask {
let url = NSURL(string: address)
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
if data == nil {
sessionEnded?(nil, error)
} else {
var parseError: NSError?
let parsedObject = NSJSONSerialization.JSONObjectWithData(data, options: nil, error:&parseError) as? NSDictionary
completionHandler?(parsedObject, parseError)
}
}
task.resume()
return task
}
And you'd invoke it like:
performURLRequest("http://www.example.com/some/path") { responseDictionary, error in
if responseDictionary == nil {
// handle error, e.g.
println(error)
return
}
// use `responseDictionary` here
}
Hi i try to find a way to parse JSON in SWIFT, this works great for me but i run into a problem.
I let the user enter a username that is used for the JSON URL -> if the user type in a valid username all works fine.
But if he enter a wrong username my parsing fails, this is correct too, but for now my app only crashes and i looking for a way to make a work around.
This is my Code where it crashes,
let url0 = NSURL(string: newUrlPath!)
let session0 = NSURLSession.sharedSession()
let task0 = session0.dataTaskWithURL(url0!, completionHandler: {data, response, error -> Void in
if (error != nil) {
println(error)
} else {
let summonorID_JSON = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as NSDictionary
The Xcode Error
Error Domain=NSURLErrorDomain Code=-1002 "The operation couldn’t be
completed. (NSURLErrorDomain error -1002.)" UserInfo=0x7c12d610
{NSErrorFailingURLKey=XX, NSErrorFailingURLStringKey=XX,
NSUnderlyingError=0x7c12c8d0 "The operation couldn’t be completed.
(kCFErrorDomainCFNetwork error -1002.)"} fatal error: unexpectedly
found nil while unwrapping an Optional value
All is fine cause this is the return page i get from my Request
https://br.api.pvp.net/api/lol/br/v1.4/summoner/by-name/smirknaitiax?api_key=5c7d4d4f-f320-43d5-8647-643c9f6ee5de
And yes he can't parse this into a NSDirectory as its no JSON that returns (as its normally is) is there a way to take care that if this page comes up (so the user entered a wrong username) that i can exit my loop/take a other way ;)?
You are using many operations which could all fail, and Swift is quite unforgiving about failure. Your code will crash if newURLPath is nil, if url0 is nil because newURLPath wasn't a valid URL.
So your URL request might return an error (the request itself failed), but you have the case that the URL request succeeded but gives unexpected results (not a JSON dictionary). Your code ending in "as NSDictionary" tells Swift: "I know I might not get a dictionary, but convert what you get to a dictionary and crash if this doesn't work". Just change this to
if let parsedJSON = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil)
{
// Will still crash if the server sends a valid JSON array
let summonorID_JSON = parsedJSON as NSDictionary
}
else
{
// data wasn't valid JSON, handle it.
}
The difference is that the optional value returned by the JSON parser will be accepted without crashing, and you check whether you received valid JSON or not.
Since you are getting 404 on this request, I assume that this will happen every time something is bad with username, you should handle server response to fit that. First thing will be to check what server returned:
let httpResp: NSHTTPURLResponse = response as NSHTTPURLRespons
At this point you can access statusCode property, that will tell you if request was good or not (404). Having that information you can decide what to do, and for example, you can modify your code something like this:
let url0 = NSURL(string: newUrlPath!)
let session0 = NSURLSession.sharedSession()
let task0 = session0.dataTaskWithURL(url0!, completionHandler: {data, response, error -> Void in
if (error != nil) {
println(error)
} else {
let httpResp: NSHTTPURLResponse = response as NSHTTPURLRespons
httpResp.statusCode != 404 {
let summonorID_JSON = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as NSDictionary
} else {
// Handle error at this point, tell user to retype username etc.
}
})
NSURL is a failable initializer and exactly this happens when you give an invalid url: It fails to initialize.
So wrap your code in an conditional unwrap:
if let url0 = NSURL(string: newUrlPath!) {
...
}
The url0 becomes nil if user enter wrong data. If you use the nil value as url0! app will crash.
When you add a ! after a variable you tell the compiler the value will not be nil.
so to avoid the crash, you have to check for nil condition before calling
let task0 = session0.dataTaskWithURL(url0!, completionHandler: {data, response, error -> Void in