Passing information from an instantiated class to the parent class.

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Hello,

I have a class library that deals with Autodesk Vault. This library will acquire a license and release a license, download and upload files and do other things. I instantiate this class from a main form. I want to communicate what the methods this class is doing to the user. For example: this class might be downloading 25 folders, I want to tell the user which folder is presently being downloaded. Or, if a license is unavailable, the "getLicense" method will automatically loop every 60 seconds until a license is acquired. I want to inform the user that the process may be delayed until a license is available. So, what is the best way to go about this?

Thank you,

Eric

Posted 2-Oct-12 6:12am

Herrwolf1

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I.explore.code 2-Oct-12 12:23pm

Web forms or win forms?

3 solutions

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Stephen Hewison · Answer 1 · 2012-10-02T06:27:00

There are two ways to do this.

Pass the parent object to the child object and call a method on the parent.

C#

public class MyForm : Form
{

  private MyWorker _worker;

  public MyForm()
  {
    _worker = new MyWorker();
  }

  public void PassMessage(string message)
  {
    //display message
  }
}

public class MyWorker
{
  private Form _form;
  public MyWorker(Form form)
  {
    _form = form;
  }

  public void doWork()
  {
    //do your work
    _form.PassMessage("My message");
  }
}

Passing in the parent object as a form irreversibly links the child component to a form. You could create an interface to allow the worker to become reusable.

C#

public interface IMessageProcessor
{
  void SendMessage(string message);
}

public class MyForm : Form, IMessageProcessor
{

  private MyWorker _worker;

  public MyForm()
  {
    _worker = new MyWorker();
  }

  public void PassMessage(string message)
  {
    //display message
  }
}

public class MyWorker
{
  private IMessageProcessor _messageProcessor;
  public MyWorker(IMessageProcessor  messageProcessor)
  {
    _messageProcessor = messageProcessor;
  }

  public void doWork()
  {
    //do your work
    _messageProcessor.PassMessage("My message");
  }
}

Using interface/abstract classes in this way is a technique called inversion of control, or IOC, sometimes also known as dependency injection.

Another way is to use events. The child object has an event which bubbles the message back up to the parent class.

C#

public class MyForm : Form
{
  private MyWorker _worker;
  public MyForm()
  {
    _worker = new MyWorker();
    _worker.OnNewMessage += new MyWorker.NewMessageHandler(_worker_OnNewMessage);
  }

  public void _worker_OnNewMessage(string message)
  {
    //display message
  }

}

public class MyWorker
{

  public delegate void NewMessageHander(string message);
  public event NewMessageHander OnNewMessage;

  public void doWork()
  {
    //do your work
    if(OnNewMessage != null)
      OnNewMessage("My message");
  }

}

OriginalGriff · Answer 2 · 2012-10-02T06:27:00

Set up public properties which indicate current download, and so forth, and have a Status property which indicates what is happening at the moment. I would also have at least one Event - StatusChanged, and possibly a NewFolderAvailable event as well. Probably, you will want to provide an Async method which uses a background worker and signals the events, rather than locking the user method, which could freeze the UI as well.

Sergey Alexandrovich Kryukov · Answer 3 · 2012-10-02T07:03:00

Solution 3

In addition to the answer by Stephen, Solution 1: this is really good to read:
http://en.wikipedia.org/wiki/Inversion_of_control[^].

[EDIT: Credit to Stephen (please see his comment below):]

It's also great to read on the wider set of SOLID principles explained here:
http://en.wikipedia.org/wiki/SOLID_%28object-oriented_design%29[^].

And everything mentioned in the "See also" section of this article is just must-read of every developer!

—SA

Posted 2-Oct-12 7:03am

Sergey Alexandrovich Kryukov

Updated 2-Oct-12 8:06am

v4

Comments

Stephen Hewison 2-Oct-12 13:36pm

Just to add a little more info. IOC or Dependency Injection is one of a set of 5 principles called the SOLID principles. By following these principles in your code design you'll produce very clear, well defined and reusable code. http://en.wikipedia.org/wiki/SOLID_(object-oriented_design)

Sergey Alexandrovich Kryukov 2-Oct-12 14:05pm

Thank you very much for this note.
I even added it to my answer, just to make it look more SOLID :-), all credit goes to you, of course.
--SA