Event is not received in user class.

Peca

Hi!
Can someone tell me what is wrong in my code? Try it with static and non-static event by commenting/uncommenting appropriate lines of code.

The name of project is "Try It" and this is main form:

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;


namespace Try_It

    public delegate void dlgt_Delegate(); // This is delegate...

    public partial class frm_Main : Form

        //public static event dlgt_Delegate evnt_Event; //... and this should be static event.

        public event dlgt_Delegate evnt_Event; //... and this should be non-static event.

        public frm_Main()

            InitializeComponent();


        private void btn_Send_Event_Click(object sender, EventArgs e)

            if (evnt_Event != null) // If someone is subscribed...

                evnt_Event(); //... tell them.


        private void btn_Exit_Click(object sender, EventArgs e)

            this.Close();

This is my class which is added by Project->Add->Class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Try_It
{
    class cls_I_am_waiting
    {
        frm_Main Main = new frm_Main();
        public cls_I_am_waiting() // This should be a constructor of a class,
        {
             //frm_Main.evnt_Event += frm_Main_evnt_Event; // I want to  be notified when button is clicked on main form (static event)...
             Main.evnt_Event += Main_evnt_Event; // I want to be notified  when button is clicked on main form (non-static event)...
        }

        //void frm_Main_evnt_Event() //... with static event.
        //{
        //    MessageBox.Show("O.K. I received it!"); //... and tell it!
        //}

        void Main_evnt_Event() //... with non-static event.
        {
            MessageBox.Show("O.K. I received it!"); //... and tell it!
        }
    }
}

Thanks.

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes12y ago
Accepted answer
This line:

new cls_I_am_waiting(this);

creates an instance of the cls_I_am_waiting class and passes its constructor a reference to the current instance of frm_Main (i.e. 'this').

I didn't bother to assign this expression to a variable as it wasn't needed elsewhere within the form.

Yes, it will also work if you remove the class level variable and just use the parameter 'Main' within the constructor because it's not accessed elsewhere in the class.

The reason I left it in was because I thought that, as you'd declared it as a class level variable in the first place, you might be going to add further methods to the class which would make use of it.
Peca12y ago
Clear. I tried with a variable and it works too. Thanks again.
Peca12y ago
Thak you Vulpes!
It works.
Can you explain to us this line of code:

new cls_I_am_waiting(this);

Also, I delete from code marked lines an everything works fine:

{
---> frm_Main Main = null; <--- deleted...

...and change from (frm_main main) to (frm_main Main)...

public cls_I_am_waiting(frm_main Main) // This should be a constructor of a class,
{
---> Main = main; <---- ... deleted

//frm_Main.evnt_Event += frm_Main_evnt_Event; // I want to be notified when button is clicked on main form (static event)...
Main.evnt_Event()...
Vulpes12y ago
There appear to be two problems:

1. I can't see where you're actually creating an instance of the cls_I_am_waiting class.

2. The cls_I_am_waiting class is creating a new instance of frm_Main whereas it should be using the existing instance.

So try it with the highlighted changes:

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

namespace Try_It
{
public delegate void dlgt_Delegate(); // This is delegate...
public partial class frm_Main : Form
{
//public static event dlgt_Delegate evnt_Event; //... and this should be static event.
public event dlgt_Delegate evnt_Event; //... and this should be non-static event.
public frm_Main()
{
InitializeComponent();
new cls_I_am_waiting(this);
}

private void btn_Send_Event_Click(object sender, EventArgs e)
{
if (evnt_Event != null) // If someone is subscribed...
evnt_Event(); //... tell them.
}

private void btn_Exit_Click(object sender, EventArgs e)
{
this.Close();
}
}
}

// This is my class which is added by Project->Add->Class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Try_It
{
class cls_I_am_waiting
{
frm_Main Main = null;

public cls_I_am_waiting(frm_main main) // This should be a constructor of a class,
{
Main = main;
//frm_Main.evnt_Event += frm_Main_evnt_Event; // I want to be notified when button is clicked on main form (static event)...
Main.evnt_Event += Main_evnt_Event; // I want to be notified when button is clicked on main form (non-static event)...
}

//void frm_Main_evnt_Event() //... with static event.
//{
// MessageBox.Show("O.K. I received it!"); //... and tell it!
//}

void Main_evnt_Event() //... with non-static event.
{
MessageBox.Show("O.K. I received it!"); //... and tell it!
}
}
}