C#

Daniel Grunwald wrote:

A "Project Resource" is shared between all forms in the project, so you can reuse the image in multiple forms.
A "Local Resource" is available only in that single form. You could create multiple local resources with the same image, but that would embed multiple copies of the image in your .exe.

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

namespace Modales_window
{
    public partial class Form2 : Form
    {
        public delegate void ClosingEventHandler();
        public event ClosingEventHandler closingeventhandler;

        public Form2()
        {
            InitializeComponent();
        }

        protected virtual void OnClosingEventHandler()
        {
            if (closingeventhandler != null)
            {
                closingeventhandler();
            } 
        }

        private void ModalesWindow2_FormClosing(object sender, FormClosingEventArgs e)
        {
            OnClosingEventHandler();
        }
    }
}

public Form1()
{
    mw2.closingeventhandler += new Form2.ClosingEventHandler(mw2_closingeventhandler);
    InitializeComponent();
}
void mw2_closingeventhandler()
{
    mw2.Dispose();
    // this is how i tried to free up the recources.
    // but this causes a loop error : (
}

private void button1_Click(object sender, EventArgs e)
{
    // Cannot access a disposed object.
    // Object name: 'Form2'.
    if (!mw2.Created)
    {
        mw2.Show();
    }
    else
    {
        //MessageBox.Show("already open", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
        if (mw2.Visible == true)
        {
            mw2.Visible = false;
        }
        else
        {
            mw2.Visible = true;
        }
    }
}

private void ModalesWindow2_FormClosing(object sender, FormClosingEventArgs e)
{
    OnClosingEventHandler();
    e.Cancel = true; // <--- surpresses the cancel event
    this.Hide();
}

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

namespace Modales_window
{
    public partial class Form1 : Form
    {

        Form2 mw2 = new Form2();

        // Form1 form = (Form1)Application.OpenForms[0];
        // Form2 form2 = (Form2)Application.OpenForms[1];

        public Form1()
        {
            mw2.closingeventhandler += new Form2.ClosingEventHandler(mw2_closingeventhandler);
            InitializeComponent();
        }
        void mw2_closingeventhandler()
        {
            //mw2.Dispose();
            //mw2.Hide();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // Cannot access a disposed object.
            // Object name: 'Form2'.
            if (!mw2.Created)
            {
                mw2.Show();
            }
            else
            {
                //MessageBox.Show("already open", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                if (mw2.Visible == true)
                {
                    mw2.Visible = false;
                }
                else
                {
                    mw2.Visible = true;
                }
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = Application.OpenForms.Count.ToString();
            GetOpenFormTitles();
        }

        private void GetOpenFormTitles()
        {
            Collection<string> formTitles = new Collection<string>();
 
            try 
            {
                foreach (Form f in Application.OpenForms) 
                {
                    // Use a thread-safe method to get all form titles.
                    formTitles.Add(GetFormTitle(f));
                }
            }
            catch (Exception ex) 
            {
                formTitles.Add("Error: " + ex.Message);
            }

            this.listBox1.DataSource = formTitles;
        }
    
        private delegate string GetFormTitleDelegate(Form f);
        private string GetFormTitle(Form f)
        {
            // Check if the form can be accessed from the current thread.
            if (!f.InvokeRequired) 
            {
                // Access the form directly.
                return f.Text;
            }
            else 
            {
                // Marshal to the thread that owns the form. 
                GetFormTitleDelegate del = GetFormTitle;
                object[] param = { f };
                System.IAsyncResult result = f.BeginInvoke(del, param);
                // Give the form's thread a chance process function.
                System.Threading.Thread.Sleep(10);
                // Check the result.
                if (result.IsCompleted) 
                {
                    // Get the function's return value.
                    return "Different thread: " + f.EndInvoke(result).ToString();
                }
                else 
                {
                    return "Unresponsive thread";
                }
            }
        }

        private void button3_Click(object sender, EventArgs e)
        {
            mw2.Close();
            //mw2.Dispose(); // causes the famous 'Cannot access a disposed object.' again 
        }
    }
}