TextField 设置属性keyboardType: TextInputType.number，设置inputFormatters: [WhitelistingTextInputFormatter.digitsOnly],

    1. TextField(
    2.   style: TextStyle(fontSize: setFont(32), color: Color(0xff4a4a4a), height: 1),
    3.   decoration: InputDecoration(
    4.     border: InputBorder.none,
    5.     hintText: '请输入提现金额',
    6.     hintStyle: TextStyle(fontSize: setFont(32), color: Color(0xffCCCCCC), height: 1),
    7.     counterText: '',
    8.   ),
    9.   controller: _tixianCtrl,
    10.   keyboardType: TextInputType.number, // 关键
    11.   inputFormatters: [WhitelistingTextInputFormatter.digitsOnly], // 关键
    12.   autocorrect: false,
    13.   maxLines: 1,
    14.   minLines: 1,
    15.   maxLength: 20,
    16.   textInputAction: TextInputAction.done,
    17. ),