Swift Defer函数似乎不适用于textField委托shouldChangeCharactersIn

Question

I'm running this code

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    //does stuff
    defer {
        moveResponder(textField) // this assigns a new first responder after the character is input
    }
    return true

Defer is supposed to run after the function ends. However, when I run this code the responder does indeed get moved to a new one and then the character change is implemented. I want it to be moved after the character is changed but the defer statement isn't working here as intended. Am I missing something with this or do I need to try something else?

Answer 1

Actually defer executes just before exiting the function… from the doc's

A defer statement is used for executing code just before transferring program control outside of the scope that the defer statement appears in.

So, when you combine that with the UITextFieldDelegate method textField(_:shouldChangeCharactersIn:replacementString:) which is simply asking if the change should be allowed, it makes sense that the move occurs before the change is committed.

If your conditions are met you should call textField.resignFirstResponder() then you can listen for the delegate method to call your function:

optional func textFieldDidEndEditing(_ textField: UITextField) {
    moveResponder(textField)
}