How do I assign an event handler in winfowms using a custom ShowDialog?

Question

I have a ShowDialog that takes several parameters. Is there a way to also pass it a delegate to handle an event on the parent form? (As opposed to instantiating the dialog, then adding the event, then calling the default ShowDialog)

Simplified sample, if I wanted a change on the dialog to reflect instantly on the opening form:

public event NameChangeEventHandler OnChange;

internal DialogResult ShowDialog(string pPersonName)
{
  using (diagSample dialog = new siagSample(pPersonName)
  {
    DialogResult result = dialog.ShowDialog();
    return result;
  }
}

public diagSample(string pPersonName)
{
  InitializeComponent();
  _PersonName = pPersonName;
}

---

Edit: My main goal is, I have a frequently used dialog that needs to call an event handler on the parent form whenever fields on the dialog are changed. Is there a way of doing this besides instantiating a New() dialog and assigning an event to its event handler each time before using ShowDialog()?

Answer 1

Well, sure, you can pass the delegate instance in the form constructor, just like the name. There is no advantage of doing this, the code will be very similar to having the event declared in the dialog form. Just non-standard.

Answer 2

You can assign events and event handlers just as you like. Here's some example code. There's two forms each with a button and a label. Form2 has a text box that you can enter tesxt in. When the button on Form2 is clicked it changes the label text and fires an event that is picked up by Form1. The label on Form1 then changes to match that on Form2.

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 dlg = new Form2();
            dlg.NameChanged += OnNameChanged;
            dlg.ShowDialog();
        }

        private void OnNameChanged(object sender, NameChangeEventArgs args)
        {
            this.label1.Text=args.NewName;
        }
    }
    public class NameChangeEventArgs : EventArgs
    {
        public NameChangeEventArgs(string name)
        {
            this.NewName=name;
        }
        public string NewName{get;private set;}
    }
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            label1.Text = textBox1.Text;
            if (this.NameChanged != null)
            {
                this.NameChanged(this, new NameChangeEventArgs(label1.Text));
            }
        }

        public event EventHandler<NameChangeEventArgs> NameChanged;
    }
}

edit - Sorry I didn't read your question correctly.

If you want to avoid this

        Form2 dlg = new Form2();
        dlg.NameChanged += OnNameChanged;
        dlg.ShowDialog();

Then you could change the Form2 constructor to:

public Form2(EventHandler<NameChangeEventArgs> eventhandler)
{
    InitializeComponent();
    NameChanged += eventhandler;
}

And then you setup and show Form2 as follows:

    Form2 dlg = new Form2(OnNameChanged);
    dlg.ShowDialog();

Unfortunately there really is now way of avoiding the += statement in assigning event handlers as they must be assigned once the parent class has been instantiated. You could of course instantiate the dialog once and just not show it until required, but then you'll have to cope with the dialog being closed and destroyed, which means not using ShowDialog, but Show instead therefore requiring you to emplace code to ensure that the dialog remains modal.