如何将验证器传递给 Flutter 中的“TextFormField”？

Question

我正在我的 flutter 应用程序中为我的表单动态生成文本字段。请检查以下代码

Widget _buildInputFields(
    String label,
    TextEditingController textController,
    TextInputType textInputType,
    IconData icon,
    Color iconColor,
  ) {
    return Container(
        margin: EdgeInsets.only(left: 20, bottom: 20),
        child: Container(
          padding: EdgeInsets.only(right: 20),
          child: Row(
            children: <Widget>[
              Flexible(
                child: TextFormField(
                  controller: textController,
                  validator: (value) {
                    if (value.isEmpty) {
                      return 'Please enter some text';
                    }
                  },
                  style: new TextStyle(color: Colors.white),
                  keyboardType: textInputType,
                  decoration: InputDecoration(
                      labelText: label,
                      fillColor: Colors.white,
                      labelStyle: TextStyle(
                          color: Colors.white, fontWeight: FontWeight.w600),
                      enabledBorder: OutlineInputBorder(
                        borderSide:
                            const BorderSide(color: Colors.white30, width: 2.0),
                        borderRadius: BorderRadius.circular(25.0),
                      ),
                      suffixIcon: IconButton(
                        icon: Icon(icon, color: iconColor),
                        onPressed: () {},
                      )),
                ),
              ),
            ],
          ),
        ));
  }

上面的方法返回一个TextFormField我需要的样式，所以我不必重新编码数百次。我只是调用方法，我得到一个新的TextFormField

无论如何，我需要进行表单验证并且每个字段都有不同的验证。在flutter中，我如何将a传递validator给 textformfield？

Answer 1

您可以简单地将验证器作为参数传递给其他验证器。您所需要的只是传入一个将字符串作为参数并返回字符串的函数。

//username validator possible structure
   Function(String) usernameValidator = (String username){
        if(username.isEmpty){
          return 'Username empty';
        }else if(username.length < 3){
          return 'Username short';
        }

        return null;
  };

  //password validator possible structure
  passwordValidator(String password){
        if(password.isEmpty){
          return 'Password empty';
        }else if(password.length < 3){
          return 'PasswordShort';
        }
        return null;
  }  



 //new build function
Widget _buildInputFields(
    String label,
    TextEditingController textController,
    TextInputType textInputType,
    IconData icon,
    Color iconColor,
    String Function(String) validator
  ) {
    return Container(
        margin: EdgeInsets.only(left: 20, bottom: 20),
        child: Container(
          padding: EdgeInsets.only(right: 20),
          child: Row(
            children: <Widget>[
              Flexible(
                child: TextFormField(
                  controller: textController,
                  validator: validator,
                  style: new TextStyle(color: Colors.white),
                  keyboardType: textInputType,
                  decoration: InputDecoration(
                      labelText: label,
                      fillColor: Colors.white,
                      labelStyle: TextStyle(
                          color: Colors.white, fontWeight: FontWeight.w600),
                      enabledBorder: OutlineInputBorder(
                        borderSide:
                            const BorderSide(color: Colors.white30, width: 2.0),
                        borderRadius: BorderRadius.circular(25.0),
                      ),
                      suffixIcon: IconButton(
                        icon: Icon(icon, color: iconColor),
                        onPressed: () {},
                      )),
                ),
              ),
            ],
          ),
        ));
  }

    //calling your function
   _buildInputFields(label, textController, textInputType, icon, iconColor, usernameValidator);
   _buildInputFields(label, textController, textInputType, icon, iconColor, passwordValidator);

Answer 2

nonybrighto答案是完全正确的，但是添加空检查后更新的代码是

// Function to create form field
Widget createFormField(String label, TextEditingController controller,
  String? Function(String?)? validator) {
return TextFormField(
  decoration: InputDecoration(labelText: label),
  controller: controller,
  autovalidate: true,
  validator: validator,
);
}

// Validator
String? Function(String?)? idValidator = (String? value) {
if (value!.isEmpty) {
  return 'Id Must be entered';
} else {
  return int.tryParse(value) == null ? 'Id Must be number' : null;
}
 };

// Finally
createFormField('Id', idController, idValidator),