final TextEditingController controller = new TextEditingController();

 @override
 void didChangeDependencies() {
    super.didChangeDependencies();
    ///通过给 controller 的 value 新创建一个 TextEditingValue
    controller.value = new TextEditingValue(text: "给输入框填入参数");
 }

 @override
  Widget build(BuildContext context) {
    return new TextField(
     ///controller
      controller: controller,
      onChanged: onChanged,
      obscureText: obscureText,
      decoration: new InputDecoration(
        hintText: hintText,
        icon: iconData == null ? null : new Icon(iconData),
      ),
    );
  }