C#

<asp:CompareValidator id="<SomeID>" runat="Server" Operator="DataTypeCheck"<br />
    Type="Date" ErrorMessage="Please enter a valid date...."<br />
    ControlToValidate="<Your TextBoxID>" />

Tony Lambert wrote:

Unfortunatelly this is the main problem: it returns the (not null) object reference whatever I've thrown exception or not.

Tony Lambert wrote:

I just throw it, it raises the exception message and the constructor returns with the object reference in the caller method instead of null.

Tony Lambert wrote:

Actually, this is the missing part of the puzzle: how to destroy or give null operand to the object in its constructor or mark it as destroyable or return with null?

<code>
public class ConditionalObject
{
   public ConditionalObject(string name)
   {
      try
      {
         if (name.Equals(""))
         {
            throw new ArgumentOutOfRangeException(this.ToString() +
            ": Unable to create new object without identifier.");
         }
      }
      catch (ArgumentOutOfRangeException AException)
      {
         Console.WriteLine(AException.Message);
      }
   }
}
</code>

using System;<br />
<br />
public class ConditionalObject<br />
{<br />
  public ConditionalObject(string name)<br />
  {<br />
    try<br />
    {<br />
      if (name.Equals(""))<br />
      {<br />
        throw new ArgumentOutOfRangeException(this.ToString() +<br />
          ": Unable to create new object without identifier.");<br />
      }<br />
    }<br />
    catch (ArgumentOutOfRangeException AException)<br />
    {<br />
      Console.WriteLine(AException.Message);<br />
    }<br />
  }<br />
}<br />
<br />
public class CallerClass<br />
{<br />
  public static void Main()<br />
  {<br />
    ConditionalObject obj = new ConditionalObject("");<br />
    Console.WriteLine(obj == null ? "null" : "not null");<br />
  }<br />
}

Tony Lambert wrote:

It is the same without catch (first example). When I throw an exception it only gets registered in an exception buffer till something catches. It does nothing with the constructor itself. That is the reason why it comes back with not null value all the time.

Tony Lambert wrote:

When I don't catch it, the application gets killed at the exit point of constuctor.

Tony Lambert wrote:

That's another problem: I need that null value.

public static ConditionalObject Create(int parm) {
    if (parm is OK) {
        return new ConditionalObject(parm);
    } else {
        // one of these could do:
        return null;
        return aDefaultConditionalObject;
        throw new ApplicationException(...);
    }
}