Returning from threading/ GCD/ completion handler
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1
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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 at 2:06
user7804097
71110
add a comment |
up vote
1
down vote
favorite
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 at 2:06
user7804097
71110
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 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 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 at 2:44
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
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 at 2:06
user7804097
71110
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 at 2:06
user7804097
71110
asked Nov 18 at 2:06
user7804097
71110
edited Nov 18 at 2:24
asked Nov 18 at 2:06
user7804097
71110
asked Nov 18 at 2:06
user7804097
71110
asked Nov 18 at 2:06
user7804097
71110
71110
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 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 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 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 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 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 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 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 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 18 at 2:25
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 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 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 at 2:44
add a comment |
2 Answers
2
active
oldest
votes
up vote
3
down vote
accepted
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 at 3:03
Ben Gottlieb
79.1k22168169
add a comment |
up vote
0
down vote
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 at 3:03
Ken Thomases
68.5k668104
add a comment |
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
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 at 3:03
Ben Gottlieb
79.1k22168169
add a comment |
up vote
3
down vote
accepted
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 at 3:03
Ben Gottlieb
79.1k22168169
add a comment |
up vote
3
down vote
accepted
up vote
3
down vote
accepted
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 at 3:03
Ben Gottlieb
79.1k22168169
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 at 3:03
Ben Gottlieb
79.1k22168169
answered Nov 18 at 3:03
Ben Gottlieb
79.1k22168169
answered Nov 18 at 3:03
Ben Gottlieb
79.1k22168169
answered Nov 18 at 3:03
Ben Gottlieb
79.1k22168169
79.1k22168169
add a comment |
add a comment |
up vote
0
down vote
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 at 3:03
Ken Thomases
68.5k668104
add a comment |
up vote
0
down vote
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 at 3:03
Ken Thomases
68.5k668104
add a comment |
up vote
0
down vote
up vote
0
down vote
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 at 3:03
Ken Thomases
68.5k668104
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 at 3:03
Ken Thomases
68.5k668104
answered Nov 18 at 3:03
Ken Thomases
68.5k668104
answered Nov 18 at 3:03
Ken Thomases
68.5k668104
answered Nov 18 at 3:03
Ken Thomases
68.5k668104
68.5k668104
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 at 2:12
@DavidBerry added. Not sure if that helps or you need even more info
– user7804097
Nov 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 at 2:44