I have a function assignName(name:) which throws an error. When that function is called from a do block with multiple catch, It shows the error as:
Errors thrown from here are not handled because the enclosing catch is not exhaustive
My Code is:
enum PersonError: ErrorType {
case IsNotAPerson
case IsNotAGoodPerson
case IsNotAValidPerson
}
func assignName(name: String?) throws {
guard name != nil else {
throw PersonError.IsNotAPerson
}
personName = name
}
func catchingSpecificError() {
do {
try assignName(nil) // Compiler Error displays at this line.
}catch PersonError.IsNotAPerson {
print("Propagated error is caught in catch on case .NotAPerson")
}
}
Thanks in Advance!
You need to include a default catch block (much like when using a switch case) to make your error handling exhaustive; in case the error thrown is not one of the ones you specify.
func catchingSpecificError() {
do {
try assignName(nil) // Compiler Error displays at this line.
}catch PersonError.IsNotAPerson {
print("Propagated error is caught in catch on case .NotAPerson")
}catch {
print("default..")
}
}
Slightly off-topic, but I assume personName = name refers to a class property personName that we cannot see in your example above.
With the default catch block added, you mention in the comments below that function catchingSpecificError() does not cast the error you expect; or rather, the default catch block catches your error.
Now, since I don't know the context of your code, I cannot infer what is actually going wrong in your case. I'll post a working example for your below where---in the context of this question---the throw and catch work as expected. Note however that your use of the guard block is somewhat out of by convention. Usually you make use of guard just like if let blocks, i.e., guard let name = name else { .., which will enter the guard block if name contains nil.
Anyway, consider the following fully working example:
enum PersonError: ErrorType {
case IsNotAPerson
case IsNotAGoodPerson
case IsNotAValidPerson
}
class Person {
var personName : String? = ""
func assignName(name: String?) throws {
guard name != nil else {
throw PersonError.IsNotAPerson
}
personName = name
}
func catchingSpecificError() {
do {
try assignName(nil)
}catch PersonError.IsNotAPerson {
print("Propagated error is caught in catch on case .NotAPerson")
}catch {
print("default..")
}
}
}
var myPerson = Person()
var myName : String? = nil
myPerson.catchingSpecificError()
/* Prints: "Propagated error is caught in catch on case .NotAPerson" */
As expected, we catch PersonError.IsNotAPerson thrown by function assignName. Hopefully you can make use of this example your get your own code (the parts that you haven't shown us in your question) working.
Related
I'm new in iOS development, so maybe I'm thinking in the wrong way. I coded a view model with a function that calls an API, and everything works fine.
class SearchCityViewModel : ViewModelProtocol {
//OBSERVABLES
var cities = PublishSubject<[City]>()
var networkError = PublishSubject<Void>()
var generalError = PublishSubject<Void>()
init(){
print("Init SearchCityViewModel")
reinit()
}
func reinit(){}
func searchCity(stringToSearch: String){
async {
do {
if stringToSearch.count>=2 {
let cities = try await(api.getCities(cityToSearch: stringToSearch)).payload!
self.cities.onNext(cities)
}
else {
self.cities.onNext([])
}
}
catch {
self.generalError.onNext(Void())
}
}
}
Now I want to handle errors. In the catch block I want to distinguish all the errors I want to handle gracefully, and for the other ones I just want to emit a general error. To do that, firstly I need to know which error is thrown when the situation I want to handle occurs. I usually do this with the debugger. For instance, I disable the internet connection, and i create a breakpoint inside the catch block. The idea is to check which error is thrown when the internet connection is disabled, in order to create a catch block for that kind of error.
Image of the debugger
I'm struggling because with the debugger I only see that is an AFError instance, but it's not telling me nothing more that can help me to catch it.
What is wrong with my workflow? Do I really need to read all the docs every time? For each library I use?
Thank you!
Perhaps you can read the articles and then you will know how to do it better, you can use the framework -oslog instead of using print function.
debugging your logging info
I found the way. What I was missing is casting the error as NSError. In this way, with the debugger is possible to see the domain and the code of the error. In the case of Alamofire, the real error is wrapped, and it's accessible through the underlyingError attribute. Once I had the domain and the code of the error, I wrote the following code:
class SearchCityViewModel : ViewModelProtocol {
//OBSERVABLES
var cities = PublishSubject<[City]>()
var networkError = PublishSubject<Void>()
var generalError = PublishSubject<Void>()
init(){
print("Init SearchCityViewModel")
reinit()
}
func reinit(){}
func searchCity(stringToSearch: String){
async {
do {
if stringToSearch.count>=2 {
let cities = try await(api.getCities(cityToSearch: stringToSearch)).payload!
self.cities.onNext(cities)
}
else {
self.cities.onNext([])
}
}
catch {
if let afError = asAFError, let underlyingError = afError.underlyingError as NSError?, underlyingError.domain == NSURLErrorDomain, underlyingError.code == NSURLErrorNotConnectedToInternet || underlyingError.code == NSURLErrorTimedOut {
self.networkError.onNext(Void())
}
else {
self.generalError.onNext(Void())
}
}
}
}
I have a service class that offers several methods that make calls to the backend, and a common theme for those methods is that I can pass callbacks for the success and error cases:
func makeCall(onSuccess: #escaping APIResponse, onError: #escaping APIError)
The type APIError is defined like so:
typealias APIError = (Error) -> Void
Furthermore I have an enum APICallError like this:
enum APICallError: Error {
case insufficientCredentials
case malformedResponse
case forbidden
}
So in my service methods I can call onError(response.result.error!) if the result contained an error object (the force unwrap is just for brevity, I'm not really doing that) and also pass my own enum value if the HTTP result is not specific enough, like onError(APICallError.insufficientCredentials).
This works fine.
The problem is, I can't figure out how to evaluate in my client code whether the error parameter that's coming in is of type APICallError and which one of those specifically. If I do:
if let callError = error as? APICallError {
if callError == .forbidden {
// ...
}
}
execution doesn't make it past the typecast. if error is APICallError also does not seem to work.
How can I cast the error parameter to my APICallError enum value that I know is in there, because when I print(error) it gives me myapp.APICallError.forbidden?
I tried to simulate what you have posted in your question in Playground, and what you are already doing should work fine for you.
if error is APICallError is also working. One possibility why the if let condition fails might be due to the error being nil. Check if that is the case by using breakpoints.
typealias APIError = (Error) -> Void
//The error type used in your question
enum APICallError: Error {
case insufficientCredentials
case malformedResponse
case forbidden
}
//A different error type for comparison
enum AnotherError: Error {
case error1
case error2
case error3
}
let apiCallError: Error = APICallError.insufficientCredentials
let anotherError: AnotherError = AnotherError.error1
//Closure definition
var onError: APIError? = { inputError in
if let apiError = inputError as? APICallError {
print("APICallError")
}
if let anotherError = inputError as? AnotherError {
print("AnotherError")
}
}
//Above defined closure is called here below...
onError?(apiCallError)
onError?(anotherError)
Console Output (Works as expected):
APICallError
AnotherError
You need to use the enum rawValue constructor.
if let callError = APICallError(rawValue: error) {
if callError == .forbidden {
...
}
} else {
// was not an APICallError value
}
I used this method very much in Swift 1.2: NSURLConnection.sendSynchronousRequest(:_:_:_) but this is apparently deprecated in iOS9. It still works however but now it uses the new Swift 2.0 Error Handling and I don't know how I will get the error message if it fails, ex. if time runs out.
I know I have to put it into a do-catch and then say try before the metho but I dont know how to catch the error message.
do {
let data = try NSURLConnection.sendSynchronousRequest(request, returningResponse: nil)
return data
}
catch _ {
return nil
}
Before I used NSError and then its description property, but now I have no clue.
Use automatic error variable, and you can cast it to NSError if you wish:
catch {
let nsError = error as NSError
print(nsError.localizedDescription)
}
You can now throw any object inheriting ErrorType, and provide custom handling in the catch sentence. You can also cast the error to NSError to access localizedDescription for handling third party errors.
Casting an enum ErrorType will produce a NSError with domain equal to the enum name, code equal to the enum value and an auto-generated localizedDescription with the following format:
The operation couldn’t be completed. (DOMAIN error CODE.)
For example, the following code:
enum AwfulError: ErrorType {
case Bad
case Worse
case Terrible
}
func throwingFunction() throws {
throw AwfulError.Worse
}
do {
try throwingFunction()
}
catch AwfulError.Bad {
print("Bad error")
}
catch let error as NSError {
print(error.localizedDescription)
}
Will print
The operation couldn’t be completed. (AwfulError error 1.)
Despite the question title specifying Swift 2, this answer is for Swift 3.
As #redent84 points out, since Swift 2 an Error object may be a home-made one. Here's a method I wrote to analyze and print the default error object available in a "catch" statement that doesn't specify any specific error type:
// Method to print an unknown Error type object to the system output.
static func printCaughtError(_ unknownError : Error) {
let objectDescription = String(describing: unknownError)
let localizedDescription = unknownError.localizedDescription
if localizedDescription != "" {
if localizedDescription.contains(objectDescription) {
print(localizedDescription)
return
}
if !objectDescription.contains(localizedDescription) {
print(objectDescription + ": " + localizedDescription)
return
}
}
print(objectDescription)
}
Then you can call it like this:
catch {
printCaughtError(error)
}
How to get the error message that is inside userInfo:
let errorMessage = (error as NSError).userInfo["message"] as? String
How can one write unit tests in Swift that communicate useful information when calling functions that can throw?
What I'd really like to be able to do is something like this:
class TestTestsTests: XCTestCase {
func doFoo() throws -> String {
// A complex operation that might throw in various places
return "foo"
}
func doBar() throws -> String {
// A complex operation that might throw in various places
return "bar"
}
func testExample() throws {
let foo = try doFoo()
let bar = try doBar()
XCTAssertNotEqual(foo, bar)
}
}
Ideally the unit test runner would stop on the line where an unhandled exception occurred, and let the user explore the stack and error message. Unfortunately, adding throws to the test function causes it to be silently skipped over (and there's a UI bug that makes it look as though the test is still being run, and getting the same result as before adding throws).
Of course it is also possible to do this:
func testExample() {
let foo = try! doFoo()
let bar = try! doBar()
XCTAssertNotEqual(foo, bar)
}
But now a failure doesn't really provide the context we need. Add a throw to doFoo, and we get a message like fatal error: 'try!' expression unexpectedly raised an error: TestTestsTests.Error(): file /Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-700.1.101.15/src/swift/stdlib/public/core/ErrorType.swift, line 50, which only gives us the line number within testExample, and not within doFoo where the error occurred. This also seems to get the debugger 'stuck' (clicking continue just returns us to the same line with the same error message) on that line, regardless of whether breakpoints are enabled, and prevents other tests from running.
So maybe we could try something like this?
func testExample() {
do {
let foo = try doFoo()
let bar = try doBar()
XCTAssertNotEqual(foo, bar)
} catch {
XCTFail("\(error)")
}
}
This runs as expected, however we can't determine which of doFoo or doBar threw the error, and also no line number information. At least we can get the error message and not prevent other tests from running.
I could go on, but the short of it is that I can't find a way to simultaneously not break the unit test running (like with try!), figure out which function threw the error, and get the error information -- Unless I do something ridiculous like:
func testExample() {
var foo: String? = nil
var bar: String? = nil
do {
foo = try doFoo()
} catch {
XCTFail("\(error)")
return
}
do {
bar = try doBar()
} catch {
XCTFail("\(error)")
return
}
if let foo = foo, bar = bar {
XCTAssertNotEqual(foo, bar)
}
}
And I still don't get to find out where in doFoo or doBar the error occurred.
Is this just the sad state of unit testing in Swift, or am I missing something?
This runs as expected, however we can't determine which of doFoo or doBar threw the error, and also no line number information.
Maybe this is just an old problem or I'm not understanding your problem, or maybe you're just kind of making a statement rather than asking a question. But with respect to the quoted statement above, you can add any information you like to the messages in XCTest Assertions.
Swift also provides the following literals:
#file String The name of the file in which it appears.
#line Int The line number on which it appears.
#column Int The column number in which it begins.
#function String The name of the declaration in which it appears.
func testExample() {
var foo: String? = nil
var bar: String? = nil
do {
foo = try doFoo()
} catch {
XCTFail("try doFoo() failed on line: \(#line) in file: \(#file) with error: \(error)")
return
}
do {
bar = try doBar()
} catch {
XCTFail("try doBar() failed on line: \(#line) in file: \(#file) with error: \(error)")
return
}
if let foo = foo, bar = bar {
XCTAssertNotEqual(foo, bar)
}
}
If you really want to go crazy with it you can add error handling to your doBar() method and that error can contain any internal information you'd like.
In fact... by implementing your own errors in your methods you might not even need to separate the methods into two blocks in your tests, just printing the error should be enough. You can put any information you like in the error message.
Anyway, I think this is an outdated issue, you can get all the information you need from the test logs - they list out all the methods that failed and even have little arrows that let you jump right to the test that failed. They then highlight the specific assertion that failed... from there it's quite easy to tell what is happening in most cases. Worst case scenario you have to set a breakpoint or two and run the test again.
You can do your own errors, using Error or LocalizedError protocols
enum Errors: Error, CustomStringConvertible {
case foo_param_is_null
case bar_param_is_null(paramIndex: Int)
var description: String {
switch self {
case .foo_param_is_null:
return "Param is null in foo"
case .bar_param_is_null(let paramIndex):
return "Param at index \(paramIndex) is null in bar"
}
}
}
func foo(_ param: Int) throws {
guard param != 0 else {
throw Errors.foo_param_is_null
}
print("foo = \(param)")
}
func bar(_ params: [Int]) throws {
if let index = params.firstIndex(where: {$0 == 0}) {
throw Errors.bar_param_is_null(paramIndex: index)
}
print("bar = \(params)")
}
do {
try foo(1)
try foo(0)
} catch {
print("\(error)")
}
do {
try bar([1,2,3])
try bar([1,0,3])
} catch {
print("\(error)")
}
Result:
foo = 1
Param is null in foo
bar = [1, 2, 3]
Param at index 1 is null in bar
And if you need even more information, you can use structures to define errors and error domains. Something like :
struct FooBarError: Error, CustomStringConvertible {
var string: String
var context: Any?
static func fooError() {
FooBarError(string: "Foo Error")
}
static func barError(context: BarErrorContext) { FooBarError(string: "Bar Error", context: context)
}
var description: String {
if let cox = context as? BarErrorContext {
return "\(string) - paramIndex: \(ctx.paramIndex) - \(ctx.insidiousReason)"
}
return string
}
}
Note:
As #ibrust proposed, you can pass #function, #line and other special parameters to your errors initialisers to provide this information
do {
try foo()
} catch {
throw(BarFooError.foo(line: #line))
}
You can also propagate the original error
do {
try bar()
} catch {
throw(BarFooError.bar(exception: error))
}
Edited:
Finally , you can also use print(Thread.callStackSymbols) in your error description, but at this point, there is a risk of confusion between debugging and testing. Just a personal thought.
I used this method very much in Swift 1.2: NSURLConnection.sendSynchronousRequest(:_:_:_) but this is apparently deprecated in iOS9. It still works however but now it uses the new Swift 2.0 Error Handling and I don't know how I will get the error message if it fails, ex. if time runs out.
I know I have to put it into a do-catch and then say try before the metho but I dont know how to catch the error message.
do {
let data = try NSURLConnection.sendSynchronousRequest(request, returningResponse: nil)
return data
}
catch _ {
return nil
}
Before I used NSError and then its description property, but now I have no clue.
Use automatic error variable, and you can cast it to NSError if you wish:
catch {
let nsError = error as NSError
print(nsError.localizedDescription)
}
You can now throw any object inheriting ErrorType, and provide custom handling in the catch sentence. You can also cast the error to NSError to access localizedDescription for handling third party errors.
Casting an enum ErrorType will produce a NSError with domain equal to the enum name, code equal to the enum value and an auto-generated localizedDescription with the following format:
The operation couldn’t be completed. (DOMAIN error CODE.)
For example, the following code:
enum AwfulError: ErrorType {
case Bad
case Worse
case Terrible
}
func throwingFunction() throws {
throw AwfulError.Worse
}
do {
try throwingFunction()
}
catch AwfulError.Bad {
print("Bad error")
}
catch let error as NSError {
print(error.localizedDescription)
}
Will print
The operation couldn’t be completed. (AwfulError error 1.)
Despite the question title specifying Swift 2, this answer is for Swift 3.
As #redent84 points out, since Swift 2 an Error object may be a home-made one. Here's a method I wrote to analyze and print the default error object available in a "catch" statement that doesn't specify any specific error type:
// Method to print an unknown Error type object to the system output.
static func printCaughtError(_ unknownError : Error) {
let objectDescription = String(describing: unknownError)
let localizedDescription = unknownError.localizedDescription
if localizedDescription != "" {
if localizedDescription.contains(objectDescription) {
print(localizedDescription)
return
}
if !objectDescription.contains(localizedDescription) {
print(objectDescription + ": " + localizedDescription)
return
}
}
print(objectDescription)
}
Then you can call it like this:
catch {
printCaughtError(error)
}
How to get the error message that is inside userInfo:
let errorMessage = (error as NSError).userInfo["message"] as? String