How can I get WPF to NOT display validation errors upon initial display of control?

Question

When I first display my screen to the user, I\'d rather not have all the validation messages show up for required fields and such before the user has had a chance to fill in

Answer 1

Just to indicate how I handled this utilising IDataErrorInfo...

I put a call to a new method called OnDataUpdated() in each setter of my view-bound property, such as:

    private string username;
    public string Username
    {
        get { return username; }
        set
        {
            username = value;
            OnDataUpdated();
        }
    }

    private string password;
    public string Password
    {
        get { return password; }
        set
        {
            password = value;
            OnDataUpdated();
        }
    }

Then inside OnDataUpdated() mark a private field boolean as true indicating data has changed for the first time (FormType was only necessary for my business case):

private void OnDataUpdated()
{
   dataChanged = true;
   // .. Any other universal RaisePropertyChanged() events you may want to call to get your UI into sync. Eg. RaisePropertyChanged(() => CanConfirm);
}

Then in my IDataErrorInfo indexer property I do the following (I split it out so 'ValidForm()' can be called manually to perform form validation too.

public string this[string columnName]
        {
            get
            {
                string result = null;
                if (columnName == "Username")
                {
                    // If other payment amounts have fully paid for balance, and cash amount has been entered, deny
                    if (!ValidForm(FormType.Step1, columnName))
                        result = "Please enter the username field.";
                }
                else if (columnName == "Password")
                {
                    if (!ValidForm(FormType.Step1, columnName))
                        result = "Please enter the password field.";
                }
                return result;
            }
        }

        /// 

        /// Test if valid form.
        /// 
        /// Specify which form we should validate.
        /// If ommitted, entire form will be validated.
        /// 
        private bool ValidForm(FormType formType, string columnName = null)
        {
            // This field is used to denote when data has changed on the form.
            // If data has changed, we know we can activate any form validation.
            // We do not activate the form validation until after a user has typed
            // something in at least.
            if (!dataChanged) return true;

            var errors = false;
            if (formType == FormType.Step1 && ((string.IsNullOrEmpty(columnName) || columnName == "Username") && string.IsNullOrEmpty(Username)))
                errors = true;
            if (formType == FormType.Step1 && ((string.IsNullOrEmpty(columnName) || columnName == "Password") && string.IsNullOrEmpty(Password)))
                errors = true;
            return !errors;
        }

Works beautifully. Now I only have validation styles appearing after a user edits the form.

If you want some extra icing on the cake, you can comment in my RaisePropertyChanged(() => CanConfirm); in the OnDataUpdated() method and bind that to your Confirm Button IsEnabled={Binding CanConfirm} with the associated property:

/// 

/// Can the user confirm step 1?
/// 
public bool CanConfirm
{
    get { return ValidForm(FormType.Step1); }
}

and your button will only be enabled when your form is valid too. :)

Enjoy! and best of luck with the behemoth that is WPF.