在 c# 中使用 window 中的委托传递数据（订阅和取消订阅）

Question

I have to pass data using the collection for two objects ( email, mobile). If I click the button subscriber or unsubscribe, the values that I enter should be stored and showed to another form if I click publish button. However, I require to use 'delegate' for this task.

This is the form that I handle value I entered

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

namespace Q1
{
    public partial class Form2 : Form
    {

        // declare delegate
        public delegate void PublishMessageDel(ArrayList publist);

        public PublishMessageDel publist = null;

        public void PublishMessage(ArrayList subscribers)
        {
            publist.Invoke(subscribers);
        }

        public Form2()
        {
            InitializeComponent();
            
        }

        private void btnBackToMain_Click(object sender, EventArgs e)
        {
            // back to first form when the buttom is clicked
            this.Hide();
            Form1 mainWindow = new Form1();
            mainWindow.ShowDialog();
            this.Close();
        }

        private void txtEmailTo_Validating(object sender, CancelEventArgs e)
        {
            if (ckbEmailTo.Checked)
            {
                IsEmailFormMatch();
            }
            else if (!ckbEmailTo.Checked)
            {
                btnSubscribe.Enabled = false;
                btnUnsubscribe.Enabled = false;

            }

        }

        private void txtTextTo_Validating(object sender, CancelEventArgs e)
        {
            if (ckbTextTo.Checked)
            {
                IsMobileFormMatch();
            }
            else if (!ckbTextTo.Checked)
            {
                btnSubscribe.Enabled = false;
                btnUnsubscribe.Enabled = false;

            }

        }


        // check valid email and button visibility
        public void IsEmailFormMatch()
        {
            string emailForm = (@"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$");

            if (!Regex.IsMatch(txtEmailTo.Text, emailForm))
            {
                MessageBox.Show("Invalid Email");
                btnSubscribe.Enabled = false;
                btnUnsubscribe.Enabled = false;
            }
            else
            {
                btnSubscribe.Enabled = true;
                btnUnsubscribe.Enabled = true;
            }
        }

        // check valid mobile and button visibility
        public void IsMobileFormMatch()
        {
            string mobileForm = (@"\d{3}-\d{3}-\d{4}");

            if (!Regex.IsMatch(txtTextTo.Text, mobileForm))
            {
                MessageBox.Show("Invalid Phone Number");
                btnSubscribe.Enabled = false;
                btnUnsubscribe.Enabled = false;
            }
            else
            {
                btnSubscribe.Enabled = true;
                btnUnsubscribe.Enabled = true;
            }
        }

        private void btnSubscribe_Click(object sender, EventArgs e)
        {
            ArrayList subscribers = new ArrayList();

            if (ckbEmailTo.Checked)
            {
                subscribers.Add(txtEmailTo.Text);
            }
            else if (ckbTextTo.Checked)
            {
                subscribers.Add(txtTextTo.Text);                
            }

            foreach (ArrayList list in subscribers)
            {
                PublishMessage(list);
            }
        }

        private void btnUnsubscribe_Click(object sender, EventArgs e)
        {
            ArrayList subscribers = new ArrayList();

            if (ckbEmailTo.Checked)
            {
                subscribers.Remove(txtEmailTo.Text);

            }
            else if (ckbTextTo.Checked)
            {
                subscribers.Remove(txtTextTo.Text);
            }

        }

    }
}

I think this part has a problem.

private void btnSubscribe_Click(object sender, EventArgs e)
        {
            ArrayList subscribers = new ArrayList();

            if (ckbEmailTo.Checked)
            {
                subscribers.Add(txtEmailTo.Text);
            }
            else if (ckbTextTo.Checked)
            {
                subscribers.Add(txtTextTo.Text);                
            }

            foreach (ArrayList list in subscribers)
            {
                PublishMessage(list);
            }
        }

        private void btnUnsubscribe_Click(object sender, EventArgs e)
        {
            ArrayList subscribers = new ArrayList();

            if (ckbEmailTo.Checked)
            {
                subscribers.Remove(txtEmailTo.Text);

            }
            else if (ckbTextTo.Checked)
            {
                subscribers.Remove(txtTextTo.Text);
            }

        }

This is the form if I click publish button, the textbox should have to show me the values that subscribed in the previous form.

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

namespace Q1
{
    public partial class Form3 : Form
    {
        Form2 fm2;
        public Form3()
        {
            InitializeComponent();
            
        }

        private void btnBackToMain3_Click(object sender, EventArgs e)
        {
            this.Hide();
            Form1 mainWindow = new Form1();
            mainWindow.ShowDialog();
            this.Close();
        }

        // change button visibility when the textbox is empty or not
        public void btnPublish_Click(object sender, EventArgs e)
        {
            Form2 fm2 = new Form2();

            var value = fm2.publist += Subscribe;
            txtSubscribers.Text += value;
            //fm2.PublishMessage();

        }

        public void Subscribe(ArrayList list)
        {
            ArrayList subscribers = list;
            txtSubscribers.Text += subscribers.ToString();
        }

        
    }
}

I think I used delegate not properly and stuck to link with it..

Answer 1

This is using delegates microsoft guide .
"A delegate is a type that safely encapsulates a method, similar to a function pointer in C and C++. Unlike C function pointers, delegates are object-oriented, type safe, and secure. The type of a delegate is defined by the name of the delegate."

So, before invoking arrSubscribers.Invoke(list);you should make a method in Form3 which takes the signature of your delegate(you receive as a parameter your ArrayList arrSubscribers ) and add the reference to fm2.arrSubscribers .

public void YourMethod(ArrayList arrSubscribers)
{
// Your code with subscribers here
}

fm2.arrSubscribers = YourMethod; or fm2.arrSubscribers += YourMethod;
Example:

    private ArrayList subscribers;
    public Form2(Form1 form)

    {
        InitializeComponent();
        form.arrSubscribers = MyMethod;
    }

    public void MyMethod(ArrayList list)
    {
        subscribers = list;
    }

    private void Click(object sender, EventArgs e)
    {
        var query = from string item in subscribers
                    select item;
        label1.Text = string.Join(", ", query);
    }