FormValidator

Android library for composable field validation.

Contents

Class	Description
FieldValidation	Contract for a single validation rule
AggregateFieldValidator	Runs a list of FieldValidation rules and returns the first failure
EmptyTextValidator	Fails if the value is an empty string
UrlValidator	Fails if the value is not a well-formed URL

Setup

Add JitPack to your settings.gradle.kts:

dependencyResolutionManagement {
    repositories {
        maven("https://jitpack.io")
    }
}

Add the dependency:

implementation("com.github.samuel8mille:form-validator:1.0.0")

Usage

Built-in validators

EmptyTextValidator and UrlValidator take a @StringRes error resource as a constructor parameter:

val emptyValidator = EmptyTextValidator(R.string.error_empty)
val urlValidator   = UrlValidator(R.string.error_invalid_url)

Custom validator

Implement FieldValidation to define your own rule:

class MaxLengthValidator(
    private val max: Int,
    @param:StringRes private val errorRes: Int,
) : FieldValidation {
    override fun isValid(value: String) = value.length <= max
    override fun errorMessageRes() = errorRes
}

Aggregate validator

Implement AggregateFieldValidator to run multiple rules in order. validate() returns the @StringRes of the first failing rule, or null if all pass:

class UrlInputValidator(
    validations: List<FieldValidation>
) : AggregateFieldValidator {
    override val validations = validations
}

val validator = UrlInputValidator(listOf(
    EmptyTextValidator(R.string.error_empty),
    UrlValidator(R.string.error_invalid_url),
))

val errorRes: Int? = validator.validate(userInput)

Pass extra rules at call time without changing the base set — useful for stateful checks like duplicate detection:

val duplicateRule = object : FieldValidation {
    override fun isValid(value: String) = existingUrls.none { it == value }
    override fun errorMessageRes() = R.string.error_duplicate
}

val errorRes = validator.validate(userInput, extra = listOf(duplicateRule))