C#

myInstance.GetType().GetProperty(whichMember)

<configuration>
 <system.net>
   <defaultProxy useDefaultCredentials="true" />
 </system.net>
</configuration>

f1.Somevariable=this.Returnvalueoftoolstripmenuitem();
f1.Show();

// UpdatableMenuItem.cs

namespace YourMdiApp
{
    public enum UpdatableMenuItem
    {
        File,
        Exit,
        View,
    }
}

// UpdateMenuItemEventArgs.cs
using System;

namespace YourMdiApp
{
    public delegate void UpdateMenuItemEventHandler(object sender, UpdateMenuItemEventArgs e);

    public class UpdateMenuItemEventArgs : EventArgs
    {
        private bool itemChecked;
        private bool enabled;
        private UpdatableMenuItem item;
        private bool visible;

        public UpdateMenuItemEventArgs(UpdatableMenuItem item, bool itemChecked, bool enabled, bool visible)
        {
            this.item = item;
            this.itemChecked = itemChecked;
            this.enabled = enabled;
            this.visible = visible;
        }

        public bool Checked
        {
            get { return itemChecked; }
        }
        public bool Enabled
        {
            get { return enabled; }
        }
        public UpdatableMenuItem Item
        {
            get { return item; }
        }
        public bool Visible
        {
            get { return visible; }
        }
    }
}

// FormChildBase.cs
using System.Windows.Forms;

namespace YourMdiApp
{
    public class FormChildBase : Form
    {
        public event UpdateMenuItemEventHandler UpdateMenuItem;

        protected virtual void OnUpdateMenuItem(UpdateMenuItemEventArgs e)
        {
            UpdateMenuItemEventHandler eh = UpdateMenuItem;
            if (eh != null)
                eh(this, e);
        }
        public void PerformUpdateMenuItem(UpdatableMenuItem item, bool itemChecked, bool enabled, bool visible)
        {
            OnUpdateMenuItem(new UpdateMenuItemEventArgs(item, itemChecked, enabled, visible));
        }
    }
}

// FormChildA.cs
using System;

namespace YourMdiApp
{
    public partial class FormChildA : FormChildBase
    {
        public FormChildA()
        {
            InitializeComponent();
            /* Clicking this form will disable the File menu on the main form */
            Click += new EventHandler(FormChildA_Click);
        }

        void FormChildA_Click(object sender, EventArgs e)
        {
            PerformUpdateMenuItem(UpdatableMenuItem.File, false, false, true);
        }
    }
}

// FormMain.cs
/* Menu and items added in designer and IsMdiContainer property set to true */
using System.Windows.Forms;

namespace YourMdiApp
{
    public partial class FormMain : Form
    {
        public FormMain()
        {
            InitializeComponent();
            FormChildA formChildA = new FormChildA();
            formChildA.UpdateMenuItem += new UpdateMenuItemEventHandler(formChildA_UpdateMenuItem);
            formChildA.MdiParent = this;
            formChildA.Show();
        }

        void formChildA_UpdateMenuItem(object sender, UpdateMenuItemEventArgs e)
        {
            ToolStripMenuItem item = null;
            switch (e.Item)
            {
                case UpdatableMenuItem.File:
                    item = fileToolStripMenuItem;
                    break;
                // ...
            }
            if (item != null)
            {
                item.Checked = e.Checked;
                item.Enabled = e.Enabled;
                item.Visible = e.Visible;
            }
        }
    }
}

// FormMain.cs
/* Menu and items added in designer and IsMdiContainer property set to true */
using System.Collections.Generic;
using System.Windows.Forms;

namespace YourMdiApp
{
    public partial class FormMain : Form
    {
        private Dictionary<UpdatableMenuItem, ToolStripMenuItem> menuItemDictionary;

        public FormMain()
        {
            InitializeComponent();
            menuItemDictionary = new Dictionary<UpdatableMenuItem, ToolStripMenuItem>()
            {
                { UpdatableMenuItem.File, fileToolStripMenuItem }
            };
            FormChildA formChildA = new FormChildA();
            formChildA.UpdateMenuItem += new UpdateMenuItemEventHandler(formChildA_UpdateMenuItem);
            formChildA.MdiParent = this;
            formChildA.Show();
        }

        void formChildA_UpdateMenuItem(object sender, UpdateMenuItemEventArgs e)
        {
            ToolStripMenuItem item;
            if (menuItemDictionary.TryGetValue(e.Item, out item))
            {
                item.Checked = e.Checked;
                item.Enabled = e.Enabled;
                item.Visible = e.Visible;
            }
        }
    }
}

AussieLew wrote:

Thanks

AussieLew wrote:

I have been struggling with fully understanding the concept of delegates, so this will prompt me to get a handle on that first.

1. Easiest but normally worst
   
   Static properties/variables as you mentioned. If using this, as they will need to be either internal or public I would strongly suggest properties with a private backing field.
2. Next best
   
   A singleton class instance. See here[^] for a good tutorial by one of the C# gods.
3. Normally the best, but can be complex to implement depending on class hierachys
   
   Let the parent form decide if the delete should be allowed and perform it. The children simply request the action and pass any required data via an event.

using System.Windows.Forms;

namespace CpDelegateSample
{
    public partial class FormMain : Form
    {
        private bool toggle;

        public FormMain()
        {
            InitializeComponent();
            toggle = false;
            FormSub formSub = new FormSub();
            formSub.DeleteRequest += new FormSub.DeleteRequestEventHandler(formSub_DeleteRequest);
            formSub.Show();
        }

        private bool formSub_DeleteRequest(string data)
        {
            // If OK, do delete and return true; otherwise, return false
            bool result = toggle;
            string message = result ? "Allowing" : "Denying";
            MessageBox.Show(string.Format("{0} {1}", message, data));
            toggle = !toggle;
            return result;
        }
    }
}

using System;
using System.Windows.Forms;

namespace CpDelegateSample
{
    public partial class FormSub : Form
    {
        public delegate bool DeleteRequestEventHandler(string data);

        public event DeleteRequestEventHandler DeleteRequest;

        public FormSub()
        {
            InitializeComponent();
            Click += new EventHandler(FormSub_Click);
        }

        void FormSub_Click(object sender, EventArgs e)
        {

            OnDeleteRequest("ABC");
            OnDeleteRequest("DEF");
        }

        protected virtual void OnDeleteRequest(string data)
        {
            DeleteRequestEventHandler eh = DeleteRequest;
            if (eh != null)
            {
                bool result = eh(data);
                string message = result ? "Allowed" : "Denied";
                MessageBox.Show(string.Format("{0} {1}", message, data));
            }
        }
    }
}

Ennis Ray Lynch, Jr. wrote:

Learn something new every day.