SmartTextBox

A WPF custom TextBox control with built-in input validation, built with Claude Opus 4.6.

Overview

SmartTextBox is a reusable, extensible WPF CustomControl that inherits from TextBox with real-time input validation support. Validation logic is decoupled through the IValidator interface — swap the Validator in XAML, no control code changes required.

Built from scratch with 3 progressive prompts, each shorter than the last, because the architecture was right from the start.

Project Structure

SmartTextBoxApp/
├── DemoApp/                             # WPF App — Validator demos
└── JamesSmartTextBox/                   # Class Library
    ├── Properties/AssemblyInfo.cs
    ├── Local/Validators/IValidator.cs   # IValidator interface + all Validators
    ├── Themes/Units/SmartTextBox.xaml   # ControlTemplate
    ├── Themes/Generic.xaml
    └── UI/Units/SmartTextBox.cs         # CustomControl (inherits TextBox)

Core Design

6 DependencyProperties:

Property	Type	Description
Header	string	Label above the input field
Placeholder	string	Watermark text
CornerRadius	CornerRadius	Border corner radius
Validator	IValidator	Validation logic interface
IsValid	bool	Whether validation passed
ErrorMessage	string	Validation error message

Validation Flow: TextChanged → Validator.Validate() → Update IsValid & ErrorMessage → ControlTemplate Triggers handle visual state

Built-in Validators

Validator	Description
RequiredValidator	Non-empty field check
EmailValidator	Email format (regex)
PasswordValidator	≥8 chars, uppercase + lowercase + digit
UrlValidator	HTTP/HTTPS format
PassportValidator	1-2 letters + 6-9 digits
CreditCardValidator	Luhn algorithm

Usage

<smart:SmartTextBox Header="Credit Card"
                    Placeholder="Enter card number"
                    Margin="0,0,0,16">
    <smart:SmartTextBox.Validator>
        <validators:CreditCardValidator/>
    </smart:SmartTextBox.Validator>
</smart:SmartTextBox>

To extend, simply implement IValidator — no changes to SmartTextBox required:

public class PhoneValidator : IValidator
{
    public string Message { get; set; } = "Invalid phone number.";
    public bool Validate(string value) => Regex.IsMatch(value ?? "", @"^\+?[\d\-\s]{10,15}$");
}

AI Prompts

Step 1. Project Setup

Framework: .NET 10
Solution Name: SmartTextBoxApp
Output Format: ZIP file
Solution Structure:
- DemoApp (WPF App)
- JamesSmartTextBox (Class Library)
DemoApp:
- SmartTextBox examples in MainWindow.xaml
JamesSmartTextBox:
- SmartTextBox.cs (CustomControl, inherits TextBox)
- SmartTextBox.xaml (ResourceDictionary)
Project Structure:
1. UI/Units/SmartTextBox.cs
2. Themes/Units/SmartTextBox.xaml
3. Themes/Generic.xaml (Merge SmartTextBox.xaml)
Important:
- Include AssemblyInfo.cs
- Generic.xaml merges SmartTextBox.xaml
- SmartTextBox.cs sets DefaultStyleKey

Step 2. Add Validation

SmartTextBox DependencyProperty (6):
- Header (string)
- PlaceHolder (string)
- CornerRadius (CornerRadius)
- Validator (IValidator)
- IsValid (bool)
- ErrorMessage (string)
IValidator:
- Message (string)
- Validate(string value) → bool
Behavior:
- Auto-validate on Text change, show red border and ErrorMessage on invalid
Validator setup:
- IValidator + 2 Validators in same file
- Path: JamesSmartTextBox/Local/Validators/IValidator.cs
DemoApp:
- Apply Validators in MainWindow.xaml
Important:
- Only 6 DPs
- No comments/regions

Step 3. Built-in Validators

Add Validators inheriting IValidator:
- Email
- Password (min 8 chars, uppercase + lowercase + numbers)
- URL
- Passport
- CreditCard
DemoApp:
- Demonstrate all Validators in MainWindow.xaml