Question

I am tryig to fade-in a windows form using c# but it doesnt seem to work after I have shown the form. Is it possible to change the forms opacity after Ive shown it?

Code:

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 ToolStrip
{
    public partial class Form1 : Form
    {
        Form ToolForm = new ToolForm();
        Form PropForm = new PropertyGrid();

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ToolForm.FormBorderStyle = FormBorderStyle.FixedToolWindow;
            ToolForm.Owner = this;
            ToolForm.Show();
            ToolForm.Location = new Point(50, 50);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            PropForm.FormBorderStyle = FormBorderStyle.FixedToolWindow;
            PropForm.Owner = this;
            PropForm.Show();
            PropForm.Location = new Point(50, 50);

            System.Timers.Timer aTimer = new System.Timers.Timer(10000);

            aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            aTimer.Interval = 2000;
            aTimer.Enabled = true;

            Console.WriteLine("Press the Enter key to exit the program.");
            Console.ReadLine();
        }

        private void OnTimedEvent(object source, ElapsedEventArgs e)
        {
            PropForm.Opacity = PropForm.Opacity - 0.25;
            Console.WriteLine(PropForm.Opacity);
        }
    }
}

Answer 1

because you r using System.Timers.Timer which is a multithread timer, in it’s OnTimedEvent() it calls control created by another thread, which cause exception.

If you use System.Windows.Forms.Timer, it will work. i tested.