Question

I have some problems with switching forms in my applications.
It have 2 forms:

• first: has one button for swith to second form;
• second: has timer for automatical switching to first form and button for manual switch to first form.

If I click button, Application executes method logOut and it works.
If it executes with events of timer – it doesn’t work. I need help to understand why it doesn’t work in this way?

Code for first form

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 Form1 : Form
    {
        private Form2 frmm2;
        public Form1()
        {
            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)
        {
            frmm2 = new Form2(this);
            frmm2.Show(this);
            this.Hide();
        }
    }
}

Second form

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;
using System.Timers;

namespace WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        private System.Timers.Timer tmr;
        private Form2 frm2;
        private Form1 frm1;

        public Form2(Form1 f1)
        {
            InitializeComponent();

            tmr = new System.Timers.Timer();
            tmr.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            tmr.Interval = 10000;
            tmr.Enabled = true;

            frm1 = f1;
            frm2 = this;
        }

        public void OnTimedEvent(object source, ElapsedEventArgs e)
        {

            tmr.Stop();
            MessageBox.Show("Before timer event");
            logOut();
            MessageBox.Show("After timer event");
        }

        private void button1_Click(object sender, EventArgs e)
        {
            logOut();
        }


        public void logOut()
        {

            if (tmr != null)
            {
                tmr.Stop();
                tmr = null;
            }

            /*
             * It doesn't work directly. I'll try to do it in another way.
            this.Hide();
            this.Owner.Show();
            this.Owner.Activate();            
             */

            frm1.Show();
            frm1.Activate();
            frm2.Close();
        }
    }
}

Thanks for answers!

Answer 1

Assuming that the LogOut method does something on the UI thread, like closing the form. The problem is that the Elapsed event is raised on a thread pool thread and not on the UI thread.

You might try System.Windows.Forms.Timer instead of System.Timers.Timer since the former will post it’s elapsed event on the UI thread.