Required static method

String? Function(String? value)? Required({
  1. String errorMessage = 'Field cannot be empty',
  2. String? next(
    1. String value
    )?,
})

Returns a validator that checks if a string is empty.

Arguments :

  • errorMessage : The error message to return if the string is empty.
  • next : A validator to run after this validator.

Usage :

TextFormField(
 validator: Validators.Required(),
),

Usage without TextFormField :

final validator = Validators.Required();

validator(''); // 'Field cannot be empty'

validator('   '); // 'Field cannot be empty'

validator('hello'); // null

You can also chain validators like this:

final validator = Validators.Required(
 next: Validators.Email(),
);

validator(''); // 'Field cannot be empty'

validator('   '); // 'Field cannot be empty'

validator('hello'); // 'Invalid email'

Implementation

static String? Function(String? value)? Required({
  String errorMessage = 'Field cannot be empty',
  String? Function(String value)? next,
}) {
  return (value) {
    if (value == null || value.trim().isEmpty) {
      return errorMessage;
    }

    if (next != null) {
      return next(value);
    }

    return null;
  };
}