Question

I’m using this code:

private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
{
    this.Show();
    this.WindowState = FormWindowState.Normal;
    //this.Location = new Point(form1_location_on_x, form1_location_on_y);
    //this.StartPosition = FormStartPosition.CenterScreen;

Either the line

this.Location = new Point(form1_location_on_x, form1_location_on_y);

or the line

this.StartPosition = FormStartPosition.CenterScreen;

are working when I’m on my original screen resolution 1920×1080, but once I’m changing the resolution to 1024×768, the Form is on the right bottom corner not hidden I see it all but it’s not in the center.

form1_location_on_x and on_y are:

form1_location_on_x = this.Location.X;
form1_location_on_y = this.Location.Y;

The question is what should I do to make it work on any other resolution like 1024×768 or any others? I tried many changes but nothing worked so far.

Answer 1

You could calculate the top and left position of your form using this formula:

int formWidth = yourForm.Width;
int formHeight = yourForm.Height;
int screenH = (Screen.PrimaryScreen.WorkingArea.Top + 
              Screen.PrimaryScreen.WorkingArea.Height) / 2;
int screenW = (Screen.PrimaryScreen.WorkingArea.Left + 
              Screen.PrimaryScreen.WorkingArea.Width) / 2;

int top = screenH - formWidth / 2;
int left = screenW - formHeight / 2;
yourForm.Location = new Point(top, left);

Of course, these days, you have the problem of dual monitors.
I don’t know if you want your form to appear always on the primary screen or you want the form appear in the current screen (the one where the form is currently displayed). In this second case you need to find where your form is displayed

private void CenterForm(Form yuorForm)
{    
    foreach(var s in Screen.AllScreens)
    {
       if(s.WorkingArea.Contains(yourForm.Location))
       {
            int screenH = s.WorkingArea.Height / 2;
            int screenW = s.WorkingArea.Width / 2;

            int top = (screenH + s.WorkingArea.Top) - formWidth / 2;
            int left = (screenW + s.WorkingArea.Left) - formHeight / 2;
            yourForm.Location = new Point(top, left);
            break;
       }
    }
}

EDIT: Thanks to @alex I will complete the answer with the information on SystemEvents class

If you want to be notified by the system when the user suddenly change the resolution of your screen you could subscribe to the event SystemEvents.DisplaySettingsChanged (using Microsoft.Win32; needed)

SystemEvents.DisplaySettingsChanged += new EventHandler(SystemEvents_DisplaySettingsChanged);  

and then handle the reposition of your form in the event

// This method is called when the display settings change.
void SystemEvents_DisplaySettingsChanged(object sender, EventArgs e)
{
    RecenterForm(yourForm);
}