C#: What is the simplest way of passing a value from one form to another

How to Pass Data Between Forms in .NET

kaufmed was probably trying link to his article here:    =)
https://www.experts-exchange.com/Programming/Languages/.NET/A_4322-How-to-Pass-Data-Between-Forms-in-NET.html

Haha...   Nice catch Idle_Mind. Guess I should check before I hit the submit button  ; )

Ok, maybe a bit more help is needed.

Basically, I am creating an instance from the first form (frmMenu). Then, I am summing two numbers. I want to output that sum back onto a label on frmMenu. I know I am close, so if someone can take a look at my actual code and let me know what I am missing:

frmMenu:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

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

        private void btnAppetizers_Click(object sender, EventArgs e)
        {
            frmAppetizers frm = new frmAppetizers();
            frm.Show();

            lblAppetizers.Text = mainForm.strAppetizers;
        }

        private frmAppetizers mainForm = null;
        public frmMenu(Form callingForm)    
        {
            mainForm = callingForm as frmAppetizers;          
            InitializeComponent();
        }
   
     }

}



frmAppetizer:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class frmAppetizers : Form
    {
        // Global Variables
        public double dblAppetizers = 0;
        public string strAppetizers = "";
     
        // The Appetizer Menu
        public frmAppetizers()
        {
            InitializeComponent();
        }
       
        //The action event that triggers everything
        private void btnSubmit_Click(object sender, EventArgs e)
        {
            //The main function is to add to values and output into a variable
            dblAppetizers = (double.Parse(txtWings.Text)) + (double.Parse(txtRings.Text));
           
            //sets the variable to a string variable
            strAppetizers = dblAppetizers.ToString();

            //Debugging action. Helps to know if the values are being added correctly and to see it output somewhere.  
            MessageBox.Show(strAppetizers);

            //Hides this form
            this.Hide();

           
        }

    }

}

Thats great! I wish I came up with that to begin with. One slight bug, I have to click the submit button on frmAppetizer twice to get it in the label on frmMenu.

Do I need to add a message box, or is there any way to hit the submit button once, then have the variable placed in the label?

Hitting it once should suffice.  Please show us the current code...  

frmAppetizers:

using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class frmAppetizers : Form
    {
        public double dblAppetizers = 0;
        public double dblRings = 10;
        public double dblWings = 24;

        public frmAppetizers()
        {
            InitializeComponent();
        }

        private void btnSubmit_Click(object sender, EventArgs e)
        {
            //The main function is to add to values and output into a variable
            dblAppetizers = (double.Parse(txtWings.Text)) + (double.Parse(txtRings.Text));

            // Set DialogResult to return execution to the main form:
            this.DialogResult = DialogResult.OK;

        }
       
    }
}


frmMenu:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

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

        private void btnAppetizers_Click(object sender, EventArgs e)
        {
            frmAppetizers frm = new frmAppetizers();
            frm.ShowDialog();
            if (frm.ShowDialog() == DialogResult.OK)
            {
                lblAppetizers.Text = frm.dblAppetizers.ToString();
            }
           
 
        }

     }
}

I'm also getting a marshal-by-reference warning. I'm not sure if that will be an issue.

You're showing the Appetizers from TWICE!

            frm.ShowDialog(); // <-- Get rid of this line
            if (frm.ShowDialog() == DialogResult.OK)
            {

Get rid of that first ShowDialog() call.  =)

Where is the warning pointing to?

Great! I didn't realize you could open and close a form from an if statement like that.

It works flawlessly now! I'm so glad. Thank you Idle_Mind and kaufmed. I really appreciate the help.

This solution is great!

You could write it like this if you prefer:

            frmAppetizers frm = new frmAppetizers();
            DialogResult result = frm.ShowDialog();
            if (result == System.Windows.Forms.DialogResult.OK)
            {
                ...
            }

I'm not sure what the difference is though.
It seems like the extra line of code is not needed.

It's just a more verbose way of doing the same thing.  The return value of ShowDialog() is stored in another locally declared variable and then you use variable in the if statement.

I prefer the original, shorter version.

That solution should have been obvious to me, but it got me back on track. I added in a few more buttons, a splash screen, a menu strip items and an output label to add all the elements together. It work pretty nice now.

Idle_Mind: The shorter version seems smoother and easy to follow.