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Expression type '@lvalue String?' is ambiguous without more context when += to UILabel.text

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0

I am trying to add the string "7" to a label when someone tabs the button labeled 7.

But when using += "7", it gives me the error "Expression type '@lvalue String?' is ambiguous without more context", when using the operator = "7" it works fine. Why doesn't += "7" work?

class NumberPadController: UIViewController 
 @IBOutlet weak var valueLabel: UILabel!

 /// set value in main vc and return to that.
 @IBAction func doneEntering(_ sender: Any) 
 guard let valueString = valueLabel.text, let valueDouble = Double(valueString), let presentingVC = self.presentingViewController as? ViewController else 
 // FIXME: Show error
 dismiss(animated: true, completion: nil)
 return
 

 presentingVC.valuePassedFromNumPad = valueDouble
 dismiss(animated: true, completion: nil)
 

 @IBAction func seven(_ sender: Any) 
 valueLabel.text += "7" // Expression type '@lvalue String?' is ambiguous without more context
 valueLabel.text = "a" // works fine
 

ios swift uilabel

share|improve this question

edited Mar 8 at 8:44

AtulParmar

1,374623

asked Mar 8 at 4:16

BruceBruce

441215

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  what the OP you expect , you want to perform some operation or else
  
  – Anbu.Karthik
  Mar 8 at 4:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You just need to unwrap the optional value before adding up. Just make sure UILabel text property it is not nil before incrementing its value: valueLabel.text! += "7"
  
  – Leo Dabus
  Mar 8 at 4:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It is worth saying that you should not use the UI to pass values around. If you need the label string value for future use you should keep a reference to its value.
  
  – Leo Dabus
  Mar 8 at 4:42
  
  

  
  
  
  

add a comment | 

0

I am trying to add the string "7" to a label when someone tabs the button labeled 7.

But when using += "7", it gives me the error "Expression type '@lvalue String?' is ambiguous without more context", when using the operator = "7" it works fine. Why doesn't += "7" work?

class NumberPadController: UIViewController 
 @IBOutlet weak var valueLabel: UILabel!

 /// set value in main vc and return to that.
 @IBAction func doneEntering(_ sender: Any) 
 guard let valueString = valueLabel.text, let valueDouble = Double(valueString), let presentingVC = self.presentingViewController as? ViewController else 
 // FIXME: Show error
 dismiss(animated: true, completion: nil)
 return
 

 presentingVC.valuePassedFromNumPad = valueDouble
 dismiss(animated: true, completion: nil)
 

 @IBAction func seven(_ sender: Any) 
 valueLabel.text += "7" // Expression type '@lvalue String?' is ambiguous without more context
 valueLabel.text = "a" // works fine
 

ios swift uilabel

share|improve this question

edited Mar 8 at 8:44

AtulParmar

1,374623

asked Mar 8 at 4:16

BruceBruce

441215

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  what the OP you expect , you want to perform some operation or else
  
  – Anbu.Karthik
  Mar 8 at 4:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You just need to unwrap the optional value before adding up. Just make sure UILabel text property it is not nil before incrementing its value: valueLabel.text! += "7"
  
  – Leo Dabus
  Mar 8 at 4:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It is worth saying that you should not use the UI to pass values around. If you need the label string value for future use you should keep a reference to its value.
  
  – Leo Dabus
  Mar 8 at 4:42
  
  

  
  
  
  

add a comment | 

I am trying to add the string "7" to a label when someone tabs the button labeled 7.

But when using += "7", it gives me the error "Expression type '@lvalue String?' is ambiguous without more context", when using the operator = "7" it works fine. Why doesn't += "7" work?

class NumberPadController: UIViewController 
 @IBOutlet weak var valueLabel: UILabel!

 /// set value in main vc and return to that.
 @IBAction func doneEntering(_ sender: Any) 
 guard let valueString = valueLabel.text, let valueDouble = Double(valueString), let presentingVC = self.presentingViewController as? ViewController else 
 // FIXME: Show error
 dismiss(animated: true, completion: nil)
 return
 

 presentingVC.valuePassedFromNumPad = valueDouble
 dismiss(animated: true, completion: nil)
 

 @IBAction func seven(_ sender: Any) 
 valueLabel.text += "7" // Expression type '@lvalue String?' is ambiguous without more context
 valueLabel.text = "a" // works fine
 

ios swift uilabel

share|improve this question

edited Mar 8 at 8:44

AtulParmar

1,374623

asked Mar 8 at 4:16

BruceBruce

441215

class NumberPadController: UIViewController 
 @IBOutlet weak var valueLabel: UILabel!

 /// set value in main vc and return to that.
 @IBAction func doneEntering(_ sender: Any) 
 guard let valueString = valueLabel.text, let valueDouble = Double(valueString), let presentingVC = self.presentingViewController as? ViewController else 
 // FIXME: Show error
 dismiss(animated: true, completion: nil)
 return
 

 presentingVC.valuePassedFromNumPad = valueDouble
 dismiss(animated: true, completion: nil)
 

 @IBAction func seven(_ sender: Any) 
 valueLabel.text += "7" // Expression type '@lvalue String?' is ambiguous without more context
 valueLabel.text = "a" // works fine
 

share|improve this question

edited Mar 8 at 8:44

AtulParmar

1,374623

asked Mar 8 at 4:16

BruceBruce

441215

share|improve this question

edited Mar 8 at 8:44

AtulParmar

1,374623

asked Mar 8 at 4:16

BruceBruce

441215

edited Mar 8 at 8:44

AtulParmar

1,374623

edited Mar 8 at 8:44

AtulParmar

1,374623

asked Mar 8 at 4:16

BruceBruce

441215

asked Mar 8 at 4:16

BruceBruce

441215

2 Answers
2

active

oldest

votes

3

The text property is optional. One way to do this safely would be to use append along with optional chaining:

valueLabel.text?.append("7")

or use += with optional chaining:

valueLabel.text? += "7"

If the label is nil, these would safely do nothing. If you'd like the label to be "7" if it was nil, then use @RickyMo's solution.

share|improve this answer

edited Mar 8 at 11:36

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How can I calculate my foodPrice label value with foodQuantity value? var quantity = 1 and foodPrice.text *= quantity. I am getting same error
  
  – Emre Değirmenci
  Mar 9 at 11:17
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @EmreDeğirmenci, you need to take the String that is in foodPrice.text, convert it to a Double, multiply that by Double(quantity), then convert that Double back to a String. Something like let price = Double(foodPrice.text ?? "") ?? 0; let total = price * Double(quantity); foodPrice.text = "(total)"
  
  – vacawama
  Mar 9 at 12:58
  

  
  
  
  

add a comment | 

4

text property is optional. To do it safely :

valueLabel.text = (valueLabel.text ?? "") + "7"

share|improve this answer

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212

add a comment | 

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3

The text property is optional. One way to do this safely would be to use append along with optional chaining:

valueLabel.text?.append("7")

or use += with optional chaining:

valueLabel.text? += "7"

If the label is nil, these would safely do nothing. If you'd like the label to be "7" if it was nil, then use @RickyMo's solution.

share|improve this answer

edited Mar 8 at 11:36

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How can I calculate my foodPrice label value with foodQuantity value? var quantity = 1 and foodPrice.text *= quantity. I am getting same error
  
  – Emre Değirmenci
  Mar 9 at 11:17
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @EmreDeğirmenci, you need to take the String that is in foodPrice.text, convert it to a Double, multiply that by Double(quantity), then convert that Double back to a String. Something like let price = Double(foodPrice.text ?? "") ?? 0; let total = price * Double(quantity); foodPrice.text = "(total)"
  
  – vacawama
  Mar 9 at 12:58
  

  
  
  
  

add a comment | 

3

The text property is optional. One way to do this safely would be to use append along with optional chaining:

valueLabel.text?.append("7")

or use += with optional chaining:

valueLabel.text? += "7"

If the label is nil, these would safely do nothing. If you'd like the label to be "7" if it was nil, then use @RickyMo's solution.

share|improve this answer

edited Mar 8 at 11:36

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How can I calculate my foodPrice label value with foodQuantity value? var quantity = 1 and foodPrice.text *= quantity. I am getting same error
  
  – Emre Değirmenci
  Mar 9 at 11:17
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @EmreDeğirmenci, you need to take the String that is in foodPrice.text, convert it to a Double, multiply that by Double(quantity), then convert that Double back to a String. Something like let price = Double(foodPrice.text ?? "") ?? 0; let total = price * Double(quantity); foodPrice.text = "(total)"
  
  – vacawama
  Mar 9 at 12:58
  

  
  
  
  

add a comment | 

The text property is optional. One way to do this safely would be to use append along with optional chaining:

valueLabel.text?.append("7")

or use += with optional chaining:

valueLabel.text? += "7"

If the label is nil, these would safely do nothing. If you'd like the label to be "7" if it was nil, then use @RickyMo's solution.

share|improve this answer

edited Mar 8 at 11:36

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

valueLabel.text?.append("7")

valueLabel.text? += "7"

share|improve this answer

edited Mar 8 at 11:36

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

answered Mar 8 at 4:30

vacawamavacawama

99.7k15178204

4

text property is optional. To do it safely :

valueLabel.text = (valueLabel.text ?? "") + "7"

share|improve this answer

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212

add a comment | 

4

text property is optional. To do it safely :

valueLabel.text = (valueLabel.text ?? "") + "7"

share|improve this answer

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212

add a comment | 

text property is optional. To do it safely :

valueLabel.text = (valueLabel.text ?? "") + "7"

share|improve this answer

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212

valueLabel.text = (valueLabel.text ?? "") + "7"

share|improve this answer

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212

answered Mar 8 at 4:23

Ricky MoRicky Mo

1,9771212