WPF TextBox Validation

Question

I have validation hooked up to a model that is bound to the TextBox container. When the window is first opened validation errors appear as the model is empty, I do

Answer 1

If you are implementing IDataErrorInfo, I've achieved this by checking for null values in the implementation of the validation logic. When creating a new window, checking for null will prevent your validation logic from firing. For example:

public partial class Product : IDataErrorInfo
{
    #region IDataErrorInfo Members

    public string Error
    {
        get { return null; }
    }

    public string this[string columnName]
    {
        get
        {
            if (columnName == "ProductName")
            {
                // Only apply validation if there is actually a value
                if (this.ProductName != null)
                {
                    if (this.ProductName.Length <= 0 || this.ProductName.Length > 25)
                        return "Product Name must be between 1 and 25 characters";
                }
            }

            return null;
        }
    }

    #endregion
}

Also, if you want to fire the validation on TextBox.LostFocus, change your binding to LostFocus, like follows: