WPF Textbox validation does not fire after contents change

Question

I am trying to validate Textbox in an WPF application that uses both Textboxes and DataGrid.

The validation fires at load - shows that textbox is empty. But when I actually type something into the textbox and then move to another one, it still shows as not valid - validation doesn't fire again.

Both the datagrid and the textboxes are using data binding in order to load and write data from database.

I created a validation rule based on this tutorial: https://learn.microsoft.com/en-us/dotnet/framework/wpf/data/how-to-implement-binding-validation.

And mostly this solution works for me - when I select a row in datagrid first, then start changing contents of textboxes - validation works. However, as mentioned previously - it doesn't properly work when the app starts and nothing is selected (and textboxes are empty).

Below fragments of my XAML file:

Here's my ValidationRule:

class ValRule : ValidationRule
{
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        if ((string)value == "")
        {
            return new ValidationResult(false, "Field cannot be empty");
        }
        else
        {
            return ValidationResult.ValidResult;
        }
    }
}

And here's fragment of my MainWindow.xaml.cs:

public partial class MainWindow : Window
{
    private printDBEntities _context = new printDBEntities();

    public MainWindow()
    {
        InitializeComponent();
    }

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {

        _context.PrintLogs.Load();


        System.Windows.Data.CollectionViewSource printLogViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("printLogViewSource")));
        printLogViewSource.Source = _context.PrintLogs.Local;

        printLogDataGrid.SelectedIndex = -1;
        //I'm setting this value to -1 so that on load my TextBoxes are empty. 
        //If i don't add this, on load my textboxes have value corrseponding to first row of datagrid.
    }

    protected override void OnClosing(CancelEventArgs e)
    {
        base.OnClosing(e);
        this._context.Dispose();
    }
    //Below normally are functions responsible for Add/Update/Remove buttons
}

Could the line printLogDataGrid.SelectedIndex = -1; when window loads be partially responsible for this problem? As mentioned in the code - if I skip this, first row of datagrid is selected on start, which means textboxes are populated with data at start as well - that would mean that user would have to delete text from each box in order to add new record.

EDIT

To clarify the situation - the textbox that is not working as expected is the nameTextBox - the only one with validation for the moment.

WPF Textbox validation does not fire after contents change

Answers (1)

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