Question

I have a simple winforms app with one form, a few controls and a business object defined like this:

public class BusinessObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, e);
        }
    }

    private string _phoneNumber;
    public string PhoneNumber
    {
        get { return _phoneNumber; }
        set
        {
            if (_phoneNumber == value)
            {
                return;
            }

            _phoneNumber = value;
            OnPropertyChanged(new PropertyChangedEventArgs("PhoneNumber"));
        }
    }

On my form, I have a textbox that is bound to the PhoneNumber property via a binding source and the data source update mode is set to OnPropertyChanged. This all works as expected. I need to do some validation on the text before it gets assigned to the PhoneNumber property on my business object. I thought that I would do this in the Validating event handler for the textbox and, if the input is invalid, I display my error provider and set e.Cancel = true. Unfortunately, this doesn’t prevent the invalid input from being bound to the PhoneNumber property. Is there an easy way to do this?

Answer 1

As suggested by mrlucmorin, I’ve changed my update data source mode from “OnPropertyChanged” to “OnValidation” so that the binding only occurs when the textbox loses and gets validated. I did implement validation in the Validating() event handler for my textbox and set e.Cancel = true when the data is invalid. Unfortunately, clicking buttons on my toolbar doesn’t seem to cause the textbox to lose focus so the Validating() event never fires but I was able to work around that by calling ValidateChildren() when a toolbar button is clicked. Thanks again to mrlucmorin and ImGreg for the suggestions that ultimately solved my problem!