Force uppercase TextFormField Flutter

Question

How can I force the TextFormField to only have uppercase letters ? textCapitalization: TextCapitalization.characters lets the user switch back to lowercase, so it isn't sufficient for what I want.

Answer 1

add textInputFormatter to text field

TextField(inputFormatters: [UpperCaseTextFormatter()]),

formatter class

class UpperCaseTextFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue) {
    return TextEditingValue(text: newValue.text.toUpperCase(), selection: newValue.selection);
  }
}