📜 FormKit – Lightweight SwiftUI Form Validation Framework

FormKit is a lightweight and flexible SwiftUI form framework designed for declarative, real-time, and user-friendly form validation. It supports per-field validation, error display, touched state tracking, and reactive form validity with a focus on SwiftUI best practices.

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🚀 Features

• ✅ Field-level validation (required, min length, custom rules)
• ✅ Live validation on user interaction
• ✅ Reactive form.isValid for controlling submit buttons
• ✅ Clean separation of concerns using FormModel and FormField
• ✅ Touched-based error visibility (errors show only after interaction)
• ✅ Full SwiftUI compatibility (iOS 15+)
• ✅ Demo app with Login and Registration flows

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🧠 How It Works

1. Define a Form

@StateObject private var form = FormModel {
    ("email", FormField(value: "", validators: [
        .required(message: "Email is required"),
        .custom { $0.contains("@") ? nil : "Invalid email" }
    ]))
}

2. Bind and Validate

TextField("Email", text: form.binding(for: "email"))
    .onChange(of: form.binding(for: "email").wrappedValue) {
        form.validate(field: "email")
    }

if let error = form.error(for: "email"), form.touched(for: "email") {
    Text(error).foregroundColor(.red)
}

3. Check Overall Validity

Button("Submit") {
    form.markAllTouched()
}
.disabled(!form.isValid)

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📱 Demo App

The demo includes:

• ✉️ Login form: email + password validation
• 📝 Registration form: name, age, optional bio
• 🗭 Navigation between login and registration
• 🎨 Custom border styling without UIKit TextFieldStyle

Start with:

HomeView()

To navigate between both forms.

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🧹 Validator Types

.required(message: String)
.minLength(Int, message: String)
.custom((Value) -> String?)  // nil means valid

More validators like .emailFormat, .matchesField, .numericOnly, etc. can be added easily.

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🧪 Future Plans

• [ ] Async validation support
• [ ] Reusable ValidatedTextField SwiftUI view
• [ ] Form reset / initial values
• [ ] Validation groups and conditional rules
• [ ] Swift Package release

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📂 Folder Structure

FormKit/
├─ Sources/
│  ├─ FormModel.swift
│  ├─ FormField.swift
│  ├─ Validator.swift
│  ├─ Protocols.swift
│  └─ FormBuilder.swift
├─ Demo/
│  ├─ HomeView.swift
│  ├─ LoginView.swift
│  ├─ RegistrationView.swift
│  └─ SharedUI.swift (validatedField)

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📦 Requirements

• iOS 15+
• Swift 5.7+
• Xcode 14+

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👥 Contributing

Found a bug or want to help extend validation? Open a PR or create an issue. Feedback is welcome!

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📄 License

MIT License. Use it, fork it, ship it 🚀