Why is Optional(“Text”) - Swift

问题

I just started with Swift. So I created a simple application with a label, button and a text field. When you click the button, the app has to change the label with the text of the text field.

class ViewController: UIViewController {
    @IBOutlet weak var textLabel: UILabel!
    @IBOutlet weak var textField: UITextField!

    @IBAction func updateButton(sender: UIButton) {
        textLabel.text = "Hi \(textField.text) "
    }

The result is

Hi Optional("TextOfTextField")

Okay. So it's a very simple question.

I hope someone can help me.

回答1:

The text of your textField is an optional value because a text field can sometimes be empty. So, use an if let to unwrap the variable and make sure it's not nil — otherwise your program could crash:

if let text: String = textField.text {
   textLabel.text = text
}

回答2:

So the problem here is that the textField's text is an optional, that you have to unwrap for using it.

Just add an ! to textField.text like this:

textLabel.text = "Hi \(textField.text!)"

Your output will now be Hi TextOfTextField

You have a few safer options to unwrap your optionals:

nil coalescing operator: ??
This will use either textField.text, or, if that's nil, use the other value provided, "?" in this case
```
textLabel.text = "Hi \(textField.text ?? "?")"
```
if let statement:
Note that this will only update your text field's text, if it's not nil. You could provide an else statement to deal with that.
```
if let text = textField.text {
    textField.text = "Hi \(text)"
}
```
guard let statement:
This works similarly like the if let statement, except that your function will end after the statement.
```
guard let text = textField.text else { return }
textField.text = "Hi \(text)"
```

Hope this helps :)

回答3:

One more way can be to use Guard to check if it is not nil.

guard let nameText = textField.text else {
    print("break if nil")
    return
}
textLabel.text = "Hi \(nameText!)"

Using guard makes sure your app fails early if the condition fails.

回答4:

In my case for Swift 4.x, I unwrapped by using below command for option Int? values or Optional list cont:

\(topics?.count ?? 0 )

回答5:

It Just a Simple using Swift here you can i just set 1 button and when it's click my textfeild text set into Lable using Swift 3

class ViewController: UIViewController {
    @IBOutlet weak var textLabel: UILabel!
    @IBOutlet weak var textField: UITextField!

    @IBAction func updateButton(sender: UIButton) {
        textLabel.text = "Hi \(textField.text!)"
    }

回答6:

I solved this problem with this for Swift 3;

self.label.text = "\(transaction.amount!)"

来源：https://stackoverflow.com/questions/33986284/why-is-optionaltext-swift

标签

ios

swift

string

optional

optional-values