Question

I’m having some trouble with date variables extracted from a masked textbox on a WinForms app.
The code which attempts to read the user input date is as follows:

DateTime datExpDate = new DateTime();
datExpDate = (DateTime)txtExpDate.ValidateText();     

But I get a NullReferenceException error, even when the masked text box is deinately not Null.

The properties on the masked text box include:

Mask: 00/00/0000
Validating Type: DateTime
TextMaskFormat: IncludeLiterals

This is exactly as I have used masked textboxes on previous apps and it worked then, so why not now?

Can anyone spot what I am doin wrong please?

Answer 1

Here is the solution from MSDN:

    private void Form1_Load(object sender, EventArgs e)
{
    maskedTextBox1.Mask = "00/00/0000";
    maskedTextBox1.ValidatingType = typeof(System.DateTime);
    maskedTextBox1.TypeValidationCompleted += new TypeValidationEventHandler(maskedTextBox1_TypeValidationCompleted);
    maskedTextBox1.KeyDown += new KeyEventHandler(maskedTextBox1_KeyDown);

    toolTip1.IsBalloon = true;
}

void maskedTextBox1_TypeValidationCompleted(object sender, TypeValidationEventArgs e)
{
    if (!e.IsValidInput)
    {
        toolTip1.ToolTipTitle = "Invalid Date";
        toolTip1.Show("The data you supplied must be a valid date in the format mm/dd/yyyy.", maskedTextBox1, 0, -20, 5000);
    }
    else
    {
        //Now that the type has passed basic type validation, enforce more specific type rules.
        DateTime userDate = (DateTime)e.ReturnValue;
        if (userDate < DateTime.Now)
        {
            toolTip1.ToolTipTitle = "Invalid Date";
            toolTip1.Show("The date in this field must be greater than today's date.", maskedTextBox1, 0, -20, 5000);
            e.Cancel = true;
        }
    }
}

// Hide the tooltip if the user starts typing again before the five-second display limit on the tooltip expires.

void maskedTextBox1_KeyDown(object sender, KeyEventArgs e)
{
    toolTip1.Hide(maskedTextBox1);
}

LINK: http://msdn.microsoft.com/en-us/library/system.windows.forms.maskedtextbox.validatingtype.aspx