validation_extensions

Flutter form field validations using dart extension methods.

Available validation extension methods

String extension methods

Check tests file for examples on how to use them or the example app.

Method	Parameters	Description
isRequired	None	Validates if the string in not empty
isEmail	None	Validates if the string is a valid email address
minLength	int min	Validates if the string length is longer than min
maxLength	int max	Validates if the string length is shorter than max
lengthRange	int min, int max	Validates if the string length is longer than min and shorter than max
match	String stringToMatch	Validates if the string is an exact match of the String stringToMatch parameter that you provide
matchPattern	String regExp	Validates if the string matches the regular expression regExp parameter that you provide
isInt	None	Validates if the string is a valid integer
isDouble	None	Validates if the string is a valid double
min	int min	Validates if the string is a valid double bigger than min
max	int max	Validates if the string is a valid double smaller than max
range	int min, int max	Validates if the string is a valid double between min and max

Note

You have to use isRequired to make a field mandatory, all other extension methods won't validate empty string, and will validate only if string is not empty which will make the field optional.

List<Function> extension methods

Method	Description
validate	execute validation functions one by one, will stop execution when it encounter a validation error and return the errorText

Usage

All extension methods return type is Function, you have to use double parentheses to execute the returned function for single validations.

Form(
      key: _formKey,
      child: TextFormField(
          validator: (v) => v.isRequired()(),
        ),
      ),

Multi validations

For multi rules validation put your validation in a list and call validate() extension method on the list, it will execute validation one by one, it will stop execution when it encounter the first validation error and return the errorText to increase performance.

Form(
      key: _formKey,
      child: Column(
        children: <Widget>[
          TextFormField(
            onChanged: (v) => password = v,
            validator: (v) => [
              v.isRequired(),
              v.minLength(8),
            ].validate(),
          ),
          TextFormField(
            validator: (v) => [
              v.isRequired(),
              v.match(password),
            ].validate(),
          ),
        ],
      ),
    ),

Custom validations

If you want to use you own validations in multi rule validation, your validation rules must be: Function that returns a Function that returns a String.

Function customValidation(v) {
	return(){
			return v != "Validation logic" ? "Invalid input" : null;
	};
}

Form(
     key: _formKey,
     child: TextFormField(
        autovalidate: true,
        validator: (v) => [
			v.isRequired(),
	        customValidation(v),
        ].validate(),
      ),
    ),

Custom error message

Pass the optional named parameter errorText to the extension method to override the default error message

Form(
      key: _formKey,
      child: TextFormField(
        onChanged: (v) => password = v,
        validator: (v) => [
          v.isRequired(
            errorText: "Password is required",
          ),
          v.minLength(
            8,
            errorText: "Password can not be less than 8 characters",
          ),
        ].validate(),
      ),
    ),