Dynamically positioning a form/dialog, whilst also keeping it all on one monitor/screen

Introduction

Sometimes you want a little more "smarts" when it comes to dynamically placing a form or dialog box, so that it doesn't position some of the form to the right or below the physical monitor, and it doesn't span monitors (in a multi-monitor setup), in much the same way as a ContextMenuStrip.

Background

I wrote this primarily for the "right-click shows dialog box" function, but it probably has other uses too. I have multiple monitors, and I just don't like seeing a dialog box split across 2 monitors.

Using the code

I want to right-click on the background in a group box. Visual Studio doesn't expose the event for this, so I had to add it into my main form's load.

        private void frmMain_Load(object sender, EventArgs e)
        {
            //this can go anywhere in the form load
            this.groupBoxTest.Click +=
                new EventHandler(this.groupBoxTest_Click);

Next is the code to handle the click event. 

        private void groupBoxTest_Click(object sender, EventArgs e)
        //Note that VisualStudio doesn't generate the click event code for a group box.
        //The hook is at the end of frmMain_Load.
        {
            GroupBox me = (GroupBox)sender;

            //The EventHandler builds an EventArgs as the second parameter,
            //but ideally I'd like a MouseEventArgs, so I simply cast e to em.
            MouseEventArgs em = (MouseEventArgs)e;

            if (em.Button == MouseButtons.Right)
            {
                frmSettings newFrmSettings = new frmSettings(this);
                MoveFormToRelativeLocation(me, new Point(em.X, em.Y), newFrmSettings);

                //Any other changes to the dialog box can go here
                //(setting text or whatever)

                newFrmSettings.ShowDialog();
            }

        }

Finally comes the location manager stuff. I actually put this in my ScreenHandler class, but I've presented it here without that reference.

        private void MoveFormToRelativeLocation(Control sender, Point pointInSender, Form form)
        {
            form.StartPosition = FormStartPosition.Manual;

            Point formTL = sender.PointToScreen(pointInSender);

            Screen myScreen = Screen.FromPoint(formTL);

            Point ScreenBR = new Point(
                myScreen.WorkingArea.Left + myScreen.WorkingArea.Width,
                myScreen.WorkingArea.Top + myScreen.WorkingArea.Height);

            if (formTL.X + form.Width > ScreenBR.X) formTL.X = ScreenBR.X - form.Width;
            if (formTL.Y + form.Height > ScreenBR.Y) formTL.Y = ScreenBR.Y - form.Height;
            if (formTL.X < 0) formTL.X = 0;
            if (formTL.Y < 0) formTL.Y = 0;

            form.Location = formTL;
        }

History

V1 20150826 082600