Passing data between forms
If I were to write a program, what methods would I use to send information from the main form of the application to a modal popup form and then pass any changes to the data back to the main form when the popup form was closed? This was an interview question that I faced and was not sure how to answer. What would your reply be?

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I would create classes or structures to represent the data being passed, and then create a constructor in the Form class for the Form to be shown that would allow me to pass the information to the class at creation time. I would also expose the information from the class using a property to allow me to retrieve the results after the Form closed. This is a very simple example to help you focus on the ideas at play. How to pass information between various classes and retrieve the information later.

Regards,
Mark 

public class Startup
{ 
 [STAThread()]
 public static void Main(string[] args)
 {
  // create some contact info to be edited
  ContactInformation info = new ContactInformation(@"Mark Belles", @"555 C# Drive"); 
  
  // create a form to display and allow the info to be edited
  ContactInformationForm form = new ContactInformationForm(info);
  
  // show the form modally
  if (form.ShowDialog() == DialogResult.OK)
  {
   // retrieve the updated info, and do something with it, perhaps save it somewhere...
   info = form.ContactInformation;
   
   // display the contact information...
   Debug.WriteLine(info);
  }  
 }
}

public class ContactInformation
{
 protected string _name;
 protected string _address;
 
 public ContactInformation(string name, string address)
 {
  _name = name;
  _address = address;
 }
 
 public string Name
 {
  get
  {
   return _name;
  }
  set
  {
   _name = value;
  }
 }
 
 public string Address
 {
  get
  { 
   return _address;
  }
  set
  {
   _address = value;
  }
 }
 
 public override string ToString()
 {
  return string.Format("ContactInformation: '{0}', '{1}'", _name, _address);
 }
}

public class ContactInformationForm : Form
{
 protected ContactInformation _info;
  
 public ContactInformationForm(ContactInformation info)
 {
  _info = info;
  // display the information for editing
 }
 
 public ContactInformation ContactInformation
 {
  get
  {
   return _info;
  }
 }
}

This was first published in February 2005

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