form_field_validator

A straightforward flutter form field validator that provides common validation options.

Usage

     // assign it directly to a TextFormField validator  
     // you don't have the pass the value your self like  
     // validator: (value) => EmailValidator(errorText: 'invalid email address').call(value)  

     TextFormField(  
         validator: EmailValidator(errorText: 'enter a valid email address')  
         );  

     // create a reusable instance  
     final requiredValidator = RequiredValidator(errorText: 'this field is required');  

     // again assign it directly to the validator  
     TextFormField(validator: requiredValidator);  

Multi rules validation

  final passwordValidator = MultiValidator([  
    RequiredValidator(errorText: 'password is required'),  
    MinLengthValidator(8, errorText: 'password must be at least 8 digits long'),  
    PatternValidator(r'(?=.*?[#?!@$%^&*-])', errorText: 'passwords must have at least one special character')  
 ]);  

  String password;  

  Form(  
    key: _formKey,  
    child: Column(children: [  
      TextFormField(  
        obscureText: true,  
        onChanged: (val) => password = val,  
        // assign the the multi validator to the TextFormField validator  
        validator: passwordValidator,  
      ),  

      // using the match validator to confirm password  
      TextFormField(  
        validator: (val) => MatchValidator(errorText: 'passwords do not match').validateMatch(val, password),  
      )  
    ]),  
  );  

Make your own validator

class LYDPhoneValidator extends TextFieldValidator {  
  // pass the error text to the super constructor  
  LYDPhoneValidator({String errorText = 'enter a valid LYD phone number'}) : super(errorText);  

  // return false if you want the validator to return error  
  // message when the value is empty.  
  @override  
   bool get ignoreEmptyValues => true;  

      @override  
      bool isValid(String value) {  
        // return true if the value is valid according the your condition  
        return hasMatch(r'^((+|00)?218|0?)?(9[0-9]{8})$', value);  
      }  
}  

   // use it by assigning it to the TextFormField validator  
   TextFormField(validator: LYDPhoneValidator());  

// you can also extend the base FieldValidator class   
// to work with non string values  

class CustomValidator extends FieldValidator<T>{  
   CustomValidator(String errorText) : super(errorText);  

      @override  
      bool isValid(T value) {  
        // TODO: implement isValid  
        return //condition;
      }  
  }