in C#, changing background image of a button after click

Question

This code does not report any error and should have work.The button background image does not change. Any idea of what could be wrong?

    void MyHandler(object sender, EventArgs e, string val)
    {
        //Process
        Process.Start(@val);
        //Change button bkground image
        var button = (Button)sender;
        button.BackgroundImage = global::Test.Properties.Resources.impOK;
    }

EDIT The event MyHandler is being called from buttons created by another event handler.

 private async void button3_Click(object sender, EventArgs e)
      {
        ...
            foreach (KeyValuePair<string, string> pair in printerDic)
            {
                //Init
                String val = pair.Value;
                String ky = pair.Key;

                //Button
                Button bt_imp = new Button();
                if (List_localServPrnLink.Contains(val))
                {
                    bt_imp.BackgroundImage = global::Test.Properties.Resources.impOK;
                }
                else
                {
                    bt_imp.BackgroundImage = global::Test.Properties.Resources.impX;
                }              
                bt_imp.Size = new System.Drawing.Size(30, 30);
                bt_imp.Location = new Point(horizotal, vertical - bt_imp.Height / 2);
                bt_imp.Click += (s, ea) => { MyHandler(sender, e, val); };//passing printer instal link when click

                ...
                vertical += 30;//Prochaine Ligne...

                this.Invoke((MethodInvoker)delegate { // runs on UI thread,
                    tabPage1.Controls.Add(bt_imp);
                    tabPage1.Controls.Add(lb_impBt);
                });

            }

... }

Answer 1

This line that you have in your button3_Click handler is incorrect:

bt_imp.Click += (s, ea) => { MyHandler(sender, e, val); };

What it is doing right now is capturing the sender/event arguments from the calling method. What you want to do is to let the MyHandler get the sender/arguments from the bt_imp click, so you need to change it to:

bt_imp.Click += (s, ea) => { MyHandler(s, ea, val); };

Which are the named parameters in your anonymous method.

The second thing you need to do is to make sure that you invoke UI changes on the UI thread. You do this quite well in the button3_Click handler, but missed it in the MyHandler routine, so just invoke that background change on the UI thread:

this.Invoke((MethodInvoker)delegate { // runs on UI thread,
                    button.BackgroundImage = global::Test.Properties.Resources.impOK;
                });

And that should take care of it.