Flutter TextField input only decimal numbers

try this:

inputFormatters: [
  FilteringTextInputFormatter.allow(RegExp(r"[0-9.]")),
  TextInputFormatter.withFunction((oldValue, newValue) {
    final text = newValue.text;
    return text.isEmpty
        ? newValue
        : double.tryParse(text) == null
            ? oldValue
            : newValue;
  }),
],

demo:

TextFormField(
  keyboardType: TextInputType.numberWithOptions(
    decimal: true,
    signed: false,
  ),
  onChanged: _yourOnChange,
  inputFormatters: [
    FilteringTextInputFormatter.allow(RegExp(r"[0-9.]")),
    TextInputFormatter.withFunction((oldValue, newValue) {
      final text = newValue.text;
      return text.isEmpty
          ? newValue
          : double.tryParse(text) == null
              ? oldValue
              : newValue;
    }),
  ],
)