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A DataAnnotations and Validation framework for Winforms

example ModelBoundForm

Mission Statement

We all have legacy code.

Rubberduck.Winforms is meant to bridge the gap between Winforms and WPF.

It enables you to:

  1. Use the same models across WPF, ASP.NET-MVC, and WINFORMS.
  2. Refactor your existing Winforms applications into a state where it is relatively simple to move your existing application to WPF. Letting you avoid that "big re-write", while still moving forward towards a modern platform.
  3. Get rid of all those ugly validation MessageBoxes and ErrorProviders by providing a more modern UI.
  4. Get rid of all that ugly boiler plate code by providing simplified API.

Minimum System Requirements

  • .Net Framework v4.0 or greater
  • Windows XP or greater


  1. From the Nuget Package Manager Console, run the following command.

    Install-Package Rubberduck.Winforms
  2. Search for "Rubberduck.Winforms" in the Package Manager and add it from there.

  3. Download the latest release from GitHub and simply copy the Rubberduck.Winforms.dll file into your project and add a reference to it.


First, define your Model class and use DataAnnotations in the normal way. Note that your model must implement INotifyPropertyChanged in order for the data binding to work correctly.

public class Person : INotifyPropertyChanged
    private string _firstName;

    public Person()
        _firstName = String.Empty;

    [RegularExpression("\\D+", ErrorMessage = "Cannot contains numbers")]
    [Display(Name="First Name")]
    public string FirstName
        get { return _firstName; }
            _firstName = value;
    public event PropertyChangedEventHandler PropertyChanged;
    private void InvokePropertyChanged(string propertyName)
        var handler = PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));

Instead of inheriting from Form, change your form to inherit from the ModelBoundForm provided by Rubberduck.Winforms. The ModelBoundForm requires that you give it a model, much like declaring a @Model in a Razor view.

public partial class PersonForm : ModelBoundForm
    public PersonForm()
        :base(model: new Person())

Then, bind your Model's property to the proper input control by creating a new TextBinding and specifing the name of the property to be bound to the control.

// Databind the Person.FirstName property to the FirstNameInput TextBox
FirstNameInput.DataBindings.Add(new TextBinding(this.Model, "FirstName"));

The ModelBoundForm can create Labels for you using the Label.For() helper.


Note that the new Label must be registered with the form in order for it to be displayed.

The ErrorLabel.For() helper creates a label to display any validation errors.


ErrorLabels will automatically display with red text if the model is in an invalid state. The helper automatically wires up an EventHandler for the Input Control's Validating event to accomplish this. The text is hidden if the model is re-validated and passes the second time.

If you wish to validate all of your controls at once, you can do so by calling the ValidateChildren() method of the Form, triggering the Validating method for all of your Input Controls. (This is actually built into Winforms, I can't take credit of this one.)

private void SubmitButton_Click(object sender, EventArgs e)
    if (this.ValidateChildren())
        // do something

Obsolte: There's no longer an need to explicitly validate the form's children if you use the CommandButton class for your buttons. CommandButtons automatically perform this validation check. Regular Winform Buttons still require that you do this check.

example ModelBoundForm

There's a full working example project in the Example directory.


Sometimes, you'll want to validate that some of the Model's properties don't conflict. Rubberduck.Winforms now supports this via the IValidatableObject interface.

public class Person : INotifyPropertyChanged, IValidatableObject

	public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        if (FirstName == LastName)
            yield return new ValidationResult("First and Last Name must be different.", new[] { "FirstName", "LastName" });

Note that you must supply member names in order for the validation errors to display properly. Rubberduck.Winforms doens't yet supply any kind of Summary field. It simply finds the proper ErrorLabel for each Model property listed in the ValidationResult for display.

ICommand and the CommandButton

As of version 0.3, Rubberduck.Winforms supplies a CommandButton that can be bound to classes that implement the ICommand interface. The button will automatically enable/disable based on the results of the CanExecute method.

Note that in order for the Enabled property of the button to be changed, the command class must raise the CanExecuteChanged event. If you pass your Model into the command's ctor, then you can easily raise the event whenever it's PropertyChanged event is raised. Other applications for ICommand may require different ways of raising the event.

public class SayHelloCommand : ICommand
    private readonly Person _person;

    public SayHelloCommand(Person person)
        _person = person;
        _person.PropertyChanged += OnModelPropertyChanged;

    private void OnModelPropertyChanged(object sender, PropertyChangedEventArgs e)
        // When the model changes, tell the world that we may need to re-evaluate CanExecute.
        CanExecuteChanged?.Invoke(this, e);

    public event EventHandler CanExecuteChanged;

    public bool CanExecute(object parameter)
        return (_person != null && _person.FirstName.Length > 3);

    public void Execute(object parameter)
        string message = (parameter as string ?? "Hello") + " " + _person.FirstName;


The command is then registered in the ModelBoundForm's constructor.

public PersonForm()
	:base(model: new Person())

	// ... other data binding ...

	//Register HelloCommand
	this.SayHelloCmdButton.Command = new SayHelloCommand(this.Model as Person);
	this.SayHelloCmdButton.CommandParameter = "Hola";

To bind a CommandParameter to a Form element, create a new Binding and add it to the CommandButton's DataBindings.

	this.SayHelloCmdButton.Command = new SayHelloCommand(this.Model as Person);
	this.SayHelloCmdButton.DataBindings.Add(new System.Windows.Forms.Binding("CommandParameter", this.LastNameInput, "Text"));

Building for Release

From Command Prompt

  1. cd into ~\Rubberduck.Winforms
  2. nuget pack Rubberduck.Winforms.csproj -Prop Configuration=Release -build