Forms, shared options and validation

Choose a field, then set its options:

KitEmailField {
    label: "Work email";
    required: true;
    pattern: ".+@example\\.com";
    pattern-message: "Use your example.com address.";
}

Fields already include label, description and error. KitFieldLabel, KitFieldDescription and KitFieldError are primitives for custom composition. Their pages list compatible controls; each reference also shows inherited properties.

Initialize validation

The complete projects use Slint Kit 0.3.0 and install the engine once per window. Export these types from your root Slint file, then initialize the Rust engine:

export { KitFormValidation, HtmlInputKind, NumberInputFormat,
    KitInputConstraints, KitValidationResult, KitValidityState } from "@kit/kit.slint";

// After App::new(), before app.run().
slint_kit::init_form_validation!(self, app);

If generated code lives in mod ui, use init_form_validation!(ui, app). Without initialization, validation-ready stays false and validity checks fail. The email, URL and text field projects contain all files.

Choose constraints

An incomplete email shows an error on blur. A second @ or an unsupported character reveals it while typing. HTML accepts name@machine: the domain does not require a dot. URLs must be absolute; https://example.comddf.dofmo@ is invalid, while mailto:a@example.com is valid. Validation does not establish that a mailbox or website exists. HTML email and URL rules.

validity exposes independent flags; value is canonical and text preserves the native draft. check-validity() checks; report-validity() also reveals the error and focuses the control. Disabled controls and read-only text fields are excluded. HTML form validation.

Guard the accepted value in Rust

A visual error does not replace validation before accepting a value. The examples configure matching FieldBinding constraints:

field.set_html_constraints(slint_kit::HtmlConstraints {
    kind: slint_kit::HtmlInputKind::Email,
    required: true,
    pattern: Some(slint_kit::HtmlPattern::compile(r".+@example\.com").expect("valid application pattern")),
    ..Default::default()
});

The engine checks before the domain parser, which receives the normalized value. An invalid draft cannot replace the last accepted value. For several fields, use HtmlFormValidation<FieldKey> and first_invalid(), or connect KitSubmitButton.validation-requested. form-no-validate bypasses this guard; reset never submits.

Mask or regex

A mask guides a fixed structure. A regex validates without rewriting the draft. For example, pattern: "[A-Z]{3}-[0-9]{4}" accepts ABC-1234, rejects abc-1234 and rejects XABC-1234. This is a shared option, not another component.

HTML does not apply pattern to textarea. For a multiline rule, use HtmlPattern in Rust and report the result through custom-validity. Invalid patterns impose no constraint, as in HTML; pattern-error exposes the diagnostic. pattern-enabled: true distinguishes an explicit empty pattern from no pattern. HTML pattern attribute.

Compose and extend

Keep the native editor for caret, selection and history. Themes, labels, messages, prefixes and suffixes remain customizable. For another skin, import the nonvisual FormConstraintState from @kit/validation.slint. Business rules, exact money, masks, OTP alphabets and zone resolution remain in typed controllers. Controllers.

The kit provides native validation based on HTML. HTTP form transport, browser autofill and platform-specific keyboards need host integration; color controls retain their typed sRGB model.