l.string()

Passes when the value is a String. Returns a StringValidator<String?>, which has every string modifier; .required() narrows the output to String. null passes until you add .required().

Signature

StringValidator<String?> string({String? message, MessageBuilder? messageBuilder})

Parameters

Parameter	Type	Meaning
message	String?	Replaces the default error message.
messageBuilder	MessageBuilder?	Builds the message from the issue. message wins when both are given. See Message builders.

Issue

Code invalidType. Default message: value must be a string, with params['expected'] set to 'string'. value is replaced by the field name when there is one.

Code generation

A String parameter maps to l.string(); DateTime and Uri parameters map to l.string() with .dateTime() for DateTime. Non-nullable parameters without a default get .required().

Example

Hand-written

final name = l.string();

Generated

required String name, // l.string().required()
String? nickname,     // l.string()
required Uri homepage, // l.string().required()

name.validate(input)+2-1

1. +valid: 'Ada'
2. +valid: null
3. -invalid: 42value must be a string

Lengths in .min(), .max() and .length() count UTF-16 code units, like String.length.