Passing data between forms using custom event handlers

Question

I have two forms (Form1 and Form2) that I would like to pass a string of characters between after a process completes on Form1.

On Form1, there is a text box that I would like to update with this string of characters. On Form2, I have a list box that contains the values that will eventually be loaded into this text box on Form1 after every process that completes. Basically what I am trying to do is to queue the next string that will be placed in the text box on Form1.

I have tried the creating a public property in Form2 as seen below:

public string NextString { get { return ListBox1.Items[ListBox1.TopIndex].ToString(); } }

Then, in Form1:

Form2 frm = new Form2();
string next = frm.NextString;
TextBox1.Text = next;

And presto. Except not. This was not working for me, unfortunately. I did some research and saw that this method was not quite the best practice and read that using event handlers was the more practical approach. So I researched those. I know that I have to create a new EventArgs class, a new public event, a firing method, how I want to handle the event, and then the handler method in Form1. This post is where I read into that.

I've played around with manipulating the answer to suit my needs:

public class StringEventArgs : EventArgs
{
    public string NextString { get; set; }
    public StringEventArgs(string data)
    {
        NextString = data;
    }
}

A new event:

public event EventHandler<ListEventArgs> NewFileAdded;

This is where I got lost. I'm having a hard time understanding what is going on now. If anyone can help me completed what I am trying to do, I would be very grateful!

are you using MVVM at all, or is all of this being done code-behind? — d.moncada, Oct 07 '17 at 04:05
It can be opened either before or after the process completes. It would not be hard to ensure that it is open before the process even starts though — Zach Yarid, Oct 07 '17 at 04:16

d.moncada · Answer 1 · 2017-10-07T19:22:57.897

2

There's no need to create your own Args class. You can accomplish this using an Action that Form2 subscribes to.

Something like:

public class Form1
{
    private Form2 _form2;

    public event Action<string> NextStringChanged;

    public class Form1()
    {
       _form2 = new Form2(this);
    }

   private void LongProcess()
   {
      _form2.Show();

      // do long process

     if (NextStringChanged != null)
     {
      NextStringChanged.Invoke(ListBox1.Items[ListBox1.TopIndex].ToString());
     }
   }
}

public class Form2
{
   public class Form2(Form1 form1)
   {
      form1.NextStringChanged += OnNextStringChanged;
   }

   private void OnNextStringChanged(string value)
   {
      // Update WPF user control here
   }
}

edited Oct 07 '17 at 19:22

answered Oct 07 '17 at 04:21

d.moncada

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I am not sure if this would make a difference in this solution, but the listbox where I'd like to grab the next value is located on Form2. It looks like this might have switched the two. Nevertheless, when I tried to implement this, I got "No overload for 'OnNextStringChanged' matches delegate 'Action' ". Any ideas? – Zach Yarid Oct 07 '17 at 16:40
sorry, see update. Note that in Form1, it is now Action – d.moncada Oct 07 '17 at 19:23
I think you flipped Form1 and Form2. The listbox is located on Form2. Form2 is the auxiliary form and Form1 is the main form. – Zach Yarid Oct 08 '17 at 03:00
@ZachYarid so, you want the value of Form2 to be notified to Form1? Does Form1 have an instance of Form2? – d.moncada Oct 08 '17 at 03:03

Dark Templar · Answer 2 · 2017-10-07T06:47:19.457

0

There are number of ways to pass data between different forms, check this out:

First create the string you want to share in Form2:

public string NextString { get { return ListBox1.Items[ListBox1.TopIndex].ToString(); } }

to access that string use this code:

string Testing = ((Form2)Application.Current.Windows[2]).NextString;

P.S. you may have to use a different index number for Form2 as I'm not sure exactly where it's located in your app.

edited Oct 07 '17 at 06:47

answered Oct 07 '17 at 06:07

Dark Templar

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For this, I get Application does not contain a definition for Current. The target .NET framework is 4.6.1, if that helps. – Zach Yarid Oct 07 '17 at 16:42

Passing data between forms using custom event handlers

2 Answers2