Returning from threading/ GCD/ completion handler
I have some logic to sign a user in from a login screen. If the login fails, I want to display a message to let the user know. If the user logs in successfully, I trigger a segue. When I test it with invalid credentials, the error alert displays as expected but the segue is still being triggered even though it's nested in an if-else statement. Why is this? How can I return out of it and avoid the else block...? I tried adding 'return' under the DispatchQ/ show alert code and that didn't have any effect.
self.login(username: usernameTextField.text!, password: passwordTextField.text!) { (error) in
if error != nil {
DispatchQueue.main.async {
self.showAlert(msg: error ?? "error")
}
} else {
DispatchQueue.main.async {
// segue code
}
}
}
login:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
}
completionHandler(nil)
}
}
swift grand-central-dispatch completionhandler ios-multithreading
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
add a comment |
I have some logic to sign a user in from a login screen. If the login fails, I want to display a message to let the user know. If the user logs in successfully, I trigger a segue. When I test it with invalid credentials, the error alert displays as expected but the segue is still being triggered even though it's nested in an if-else statement. Why is this? How can I return out of it and avoid the else block...? I tried adding 'return' under the DispatchQ/ show alert code and that didn't have any effect.
self.login(username: usernameTextField.text!, password: passwordTextField.text!) { (error) in
if error != nil {
DispatchQueue.main.async {
self.showAlert(msg: error ?? "error")
}
} else {
DispatchQueue.main.async {
// segue code
}
}
}
login:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
}
completionHandler(nil)
}
}
swift grand-central-dispatch completionhandler ios-multithreading
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
Your sure that’s the only way to trigger the segue? That the callback isn’t being executed twice? From the code you have here it appears it should work as expected which means the problem is most likely elsewhere. Best help would probably be to show login as well.
– David Berry
Nov 18 '18 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 '18 at 2:25
@davidBerry also, yes, positive its the only segue trigger. If I remove it it works as intended - if i add a print statement to the else block, the print runs...
– user7804097
Nov 18 '18 at 2:44
add a comment |
I have some logic to sign a user in from a login screen. If the login fails, I want to display a message to let the user know. If the user logs in successfully, I trigger a segue. When I test it with invalid credentials, the error alert displays as expected but the segue is still being triggered even though it's nested in an if-else statement. Why is this? How can I return out of it and avoid the else block...? I tried adding 'return' under the DispatchQ/ show alert code and that didn't have any effect.
self.login(username: usernameTextField.text!, password: passwordTextField.text!) { (error) in
if error != nil {
DispatchQueue.main.async {
self.showAlert(msg: error ?? "error")
}
} else {
DispatchQueue.main.async {
// segue code
}
}
}
login:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
}
completionHandler(nil)
}
}
swift grand-central-dispatch completionhandler ios-multithreading
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
I have some logic to sign a user in from a login screen. If the login fails, I want to display a message to let the user know. If the user logs in successfully, I trigger a segue. When I test it with invalid credentials, the error alert displays as expected but the segue is still being triggered even though it's nested in an if-else statement. Why is this? How can I return out of it and avoid the else block...? I tried adding 'return' under the DispatchQ/ show alert code and that didn't have any effect.
self.login(username: usernameTextField.text!, password: passwordTextField.text!) { (error) in
if error != nil {
DispatchQueue.main.async {
self.showAlert(msg: error ?? "error")
}
} else {
DispatchQueue.main.async {
// segue code
}
}
}
login:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
}
completionHandler(nil)
}
}
swift grand-central-dispatch completionhandler ios-multithreading
swift grand-central-dispatch completionhandler ios-multithreading
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
edited Nov 18 '18 at 2:24
user7804097
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
asked Nov 18 '18 at 2:06
user7804097user7804097
83110
83110
Your sure that’s the only way to trigger the segue? That the callback isn’t being executed twice? From the code you have here it appears it should work as expected which means the problem is most likely elsewhere. Best help would probably be to show login as well.
– David Berry
Nov 18 '18 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 '18 at 2:25
@davidBerry also, yes, positive its the only segue trigger. If I remove it it works as intended - if i add a print statement to the else block, the print runs...
– user7804097
Nov 18 '18 at 2:44
add a comment |
Your sure that’s the only way to trigger the segue? That the callback isn’t being executed twice? From the code you have here it appears it should work as expected which means the problem is most likely elsewhere. Best help would probably be to show login as well.
– David Berry
Nov 18 '18 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 '18 at 2:25
@davidBerry also, yes, positive its the only segue trigger. If I remove it it works as intended - if i add a print statement to the else block, the print runs...
– user7804097
Nov 18 '18 at 2:44
Your sure that’s the only way to trigger the segue? That the callback isn’t being executed twice? From the code you have here it appears it should work as expected which means the problem is most likely elsewhere. Best help would probably be to show login as well.
– David Berry
Nov 18 '18 at 2:12
Your sure that’s the only way to trigger the segue? That the callback isn’t being executed twice? From the code you have here it appears it should work as expected which means the problem is most likely elsewhere. Best help would probably be to show login as well.
– David Berry
Nov 18 '18 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 '18 at 2:25
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 '18 at 2:25
@davidBerry also, yes, positive its the only segue trigger. If I remove it it works as intended - if i add a print statement to the else block, the print runs...
– user7804097
Nov 18 '18 at 2:44
@davidBerry also, yes, positive its the only segue trigger. If I remove it it works as intended - if i add a print statement to the else block, the print runs...
– user7804097
Nov 18 '18 at 2:44
add a comment |
2 Answers
2
active
oldest
votes
You're running the completion handler either way; if you get an error back, you're calling it, but then you fall through and run it with nil. Try this:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
} else {
completionHandler(nil)
}
}
}
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
add a comment |
Your login function calls completionHandler twice in the error case. The if falls through to the following statement. You should either put the following statement in an else block, or return from the true block.
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You're running the completion handler either way; if you get an error back, you're calling it, but then you fall through and run it with nil. Try this:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
} else {
completionHandler(nil)
}
}
}
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
add a comment |
You're running the completion handler either way; if you get an error back, you're calling it, but then you fall through and run it with nil. Try this:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
} else {
completionHandler(nil)
}
}
}
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
add a comment |
You're running the completion handler either way; if you get an error back, you're calling it, but then you fall through and run it with nil. Try this:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
} else {
completionHandler(nil)
}
}
}
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
You're running the completion handler either way; if you get an error back, you're calling it, but then you fall through and run it with nil. Try this:
func login(username: String, password: String, completionHandler: @escaping (_ error: String?) -> ()) {
SessionHelper.shared.logUserIn(withUsername: username, andPassword: password) { (error) in
if let err = error {
completionHandler(err)
} else {
completionHandler(nil)
}
}
}
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
answered Nov 18 '18 at 3:03
Ben GottliebBen Gottlieb
79.4k22168169
79.4k22168169
add a comment |
add a comment |
Your login function calls completionHandler twice in the error case. The if falls through to the following statement. You should either put the following statement in an else block, or return from the true block.
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
add a comment |
Your login function calls completionHandler twice in the error case. The if falls through to the following statement. You should either put the following statement in an else block, or return from the true block.
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
add a comment |
Your login function calls completionHandler twice in the error case. The if falls through to the following statement. You should either put the following statement in an else block, or return from the true block.
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
Your login function calls completionHandler twice in the error case. The if falls through to the following statement. You should either put the following statement in an else block, or return from the true block.
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
answered Nov 18 '18 at 3:03
Ken ThomasesKen Thomases
69.6k669106
69.6k669106
add a comment |
add a comment |
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Your sure that’s the only way to trigger the segue? That the callback isn’t being executed twice? From the code you have here it appears it should work as expected which means the problem is most likely elsewhere. Best help would probably be to show login as well.
– David Berry
Nov 18 '18 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 '18 at 2:25
@davidBerry also, yes, positive its the only segue trigger. If I remove it it works as intended - if i add a print statement to the else block, the print runs...
– user7804097
Nov 18 '18 at 2:44