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Khoa Pham
Khoa Pham

Posted on • Updated on

How to make simple form validator in Swift

Sometimes we want to validate forms with many fields, for example name, phone, email, and with different rules. If validation fails, we show error message.

We can make simple Validator and Rule

class Validator {
    func validate(text: String, with rules: [Rule]) -> String? {
        return rules.compactMap({ $0.check(text) }).first
    }

    func validate(input: InputView, with rules: [Rule]) {
        guard let message = validate(text: input.textField.text ?? "", with: rules) else {
            input.messageLabel.isHidden = true
            return
        }

        input.messageLabel.isHidden = false
        input.messageLabel.text = message
    }
}

struct Rule {
    // Return nil if matches, error message otherwise
    let check: (String) -> String?

    static let notEmpty = Rule(check: {
        return $0.isEmpty ? "Must not be empty" : nil
    })

    static let validEmail = Rule(check: {
        let regex = #"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,64}"#

        let predicate = NSPredicate(format: "SELF MATCHES %@", regex)
        return predicate.evaluate(with: $0) ? nil : "Must have valid email"
    })

    static let countryCode = Rule(check: {
        let regex = #"^\+\d+.*"#

        let predicate = NSPredicate(format: "SELF MATCHES %@", regex)
        return predicate.evaluate(with: $0) ? nil : "Must have prefix country code"
    })
}
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Then we can use very expressively

let validator = Validator()
validator.validate(input: inputView, with: [.notEmpty, .validEmail])
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Then a few tests to make sure it works

class ValidatorTests: XCTestCase {
    let validator = Validator()

    func testEmpty() {
        XCTAssertNil(validator.validate(text: "a", with: [.notEmpty]))
        XCTAssertNotNil(validator.validate(text: "", with: [.notEmpty]))
    }

    func testEmail() {
        XCTAssertNil(validator.validate(text: "onmyway133@gmail.com", with: [.validEmail]))
        XCTAssertNotNil(validator.validate(text: "onmyway133", with: [.validEmail]))
        XCTAssertNotNil(validator.validate(text: "onmyway133.com", with: [.validEmail]))
    }

    func testCountryCode() {
        XCTAssertNil(validator.validate(text: "+47 11 222 333", with: [.countryCode]))
        XCTAssertNotNil(validator.validate(text: "11 222 333", with: [.countryCode]))
        XCTAssertNotNil(validator.validate(text: "47 11 222 333", with: [.countryCode]))
    }
}
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Discussion (3)

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saroar profile image
Saroar Khandoker

hi what is InputView? where is coming from ?

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texyz profile image
Texyz

hi what is InputView? where is coming from ?

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nexxado profile image
Netanel Draiman • Edited on

InputView probably looks something like this:

struct InputView {
    let textField: UITextField
    let messageLabel: UILabel
}
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