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Input predictable on iOS

Whenever a user provides input, there should be no change of context. Example of changing context include, but are not limited to: automatically submitting data, opening a new screen or moving to another element. Input should have predictable effects.

With iOS, be careful when using UITextFieldDelegate methods. Do not trigger a change of context when text changes.

extension ApptViewController: UITextFieldDelegate {
  func textField(_ textField: UITextField,
                  shouldChangeCharactersIn range: NSRange,
                  replacementString string: String) -> Bool {
      // Do not change context
      return true


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