Select all text in a UITextField using Swift

In case you need this to work with a SwiftUI TextField, you can use Introspect:

import Introspect

private class TextFieldObserver: NSObject {
    @objc
    func textFieldDidBeginEditing(_ textField: UITextField) {
        textField.selectAll(nil)
    }
}

struct ContentView {
    private let textFieldObserver = TextFieldObserver()
    var body: some View {
        TextField(...)
            .introspectTextField { textField in
                textField.addTarget(
                    self.textFieldObserver,
                    action: #selector(TextFieldObserver.textFieldDidBeginEditing),
                    for: .editingDidBegin
                )
            }
    }
}

Note that you shouldn't override textField.delegate as SwiftUI sets up its own delegate that is supposed to be hidden from you.

It works in the same way like in Objective-C:

textField.becomeFirstResponder()

textField.selectedTextRange = textField.textRange(from: textField.beginningOfDocument, to: textField.endOfDocument)

Try this:

Make sure you conform to the UITextFieldDelegate and implement:

func textFieldDidBeginEditing(_ textField: UITextField) {
        //highlights all text
        textField.selectedTextRange = textField.textRange(from: textField.beginningOfDocument, to: textField.endOfDocument)
}

textField.becomeFirstResponder()
textField.selectAll(nil)