測(cè)試反饋輸入框不允許輸入特殊字符，于是我就想怎么處理，慢慢寫下了以下代碼

final MyInputFormatter _inputFormatter = MyInputFormatter();

// ...

Container(
  child: TextField(
        controller: insAccountController,
        inputFormatters: [_inputFormatter],
     ), 
),


class MyInputFormatter extends FilteringTextInputFormatter {
  MyInputFormatter() : super.allow(RegExp(r'^[a-zA-Z0-9_.]+$'));

  @override
  TextEditingValue formatEditUpdate(
      TextEditingValue oldValue, TextEditingValue newValue) {

    final filteredText =
        newValue.text.replaceAll(RegExp(r'[^a-zA-Z0-9_.]+'), '');


    if (filteredText != newValue.text) {
      return TextEditingValue(
        text: filteredText,
        selection: TextSelection.collapsed(offset: filteredText.length),
      );
    }

    return newValue;
  }
}