Is it possible to write new attached property like Validation.Errors, say MyValidation.XYZ

Question

Hello,

I would like to use some set of my own different attached properties not defined in Validation.cs.

Actually I've tried all known possible ways including AddValueChanged for existing public Validation.<DependencyProperty>, but no have no luck - I get only a default value of new property and has no chance to get an actualization event fired.

Thank you for assistance.

Answer 1

Hi,@Alexander Landa. Welcome to Microsoft Q&A. It is possible to create your own attached properties in WPF, similar to Validation.Errors, for various purposes such as custom validation, behavior addition, or data binding facilitation.

Here's an example of create a custom attached property MyValidation.XYZ:

<StackPanel>

    <TextBox Width="100" Height="60" Text="{Binding MyValue}" local:MyValidation.XYZ="{Binding MyValue}" />

</StackPanel>

Codebehind:

public partial class MainWindow : Window,INotifyPropertyChanged
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }
    private string myValue;

    public string MyValue
    {
        get { return myValue; }
        set { myValue = value; OnPropertyChanged(); }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([CallerMemberName] string name = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
    }

}
public static class MyValidation
{
    public static readonly DependencyProperty XYZProperty =
        DependencyProperty.RegisterAttached("XYZ", typeof(string), typeof(MyValidation),
            new PropertyMetadata(null, OnXYZPropertyChanged));

    public static string GetXYZ(DependencyObject obj)
    {
        return (string)obj.GetValue(XYZProperty);
    }

    public static void SetXYZ(DependencyObject obj, string value)
    {
        obj.SetValue(XYZProperty, value);
    }

    private static void OnXYZPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // This method will be called whenever the value of XYZ property changes
        // You can perform any necessary actions here
        string newValue = (string)e.NewValue;
        string oldValue = (string)e.OldValue;

        // Example: Logging the change
        System.Diagnostics.Debug.WriteLine($"XYZ property changed from '{oldValue}' to '{newValue}'");
    }
}

The result:

When MyValue changes, a meesage is displayed in the output window.

XYZ property changed from '' to 'FFF' XYZ property changed from 'FFF' to 'DDD'

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