Determining if a form is completely off screen

I am developing an application that remembers the user's preferences as to where the form was last located on the screen. In some instances the user will have it on a secondary screen, and then fire the app up later without the second screen (sometimes having the form appear off screen). Other times the user will change their resolution resulting in a similar effect.

I was hoping to do this checking in the Form_Shown event handler. Basically I want to determine whether the form is completely off screen so I can re-position it.

Any advice?

Solution 1:

Check with this function if Form is fully on screen:

public bool IsOnScreen( Form form )
{
   Screen[] screens = Screen.AllScreens;
   foreach( Screen screen in screens )
   {
      Rectangle formRectangle = new Rectangle( form.Left, form.Top, 
                                               form.Width, form.Height );

      if( screen.WorkingArea.Contains( formRectangle ) )
      {
         return true;
      }
   }

   return false;
}

Checking only top left point if it's on screen:

public bool IsOnScreen( Form form )
{
   Screen[] screens = Screen.AllScreens;
   foreach( Screen screen in screens )
   {
      Point formTopLeft = new Point( form.Left, form.Top );

      if( screen.WorkingArea.Contains( formTopLeft ) )
      {
         return true;
      }
   }

   return false;
}

Solution 2:

Combining all the solutions above with the "IntersectsWith"-method and LINQ-extensions give us in short:

public bool IsOnScreen(Form form) 
{
   // Create rectangle
   Rectangle formRectangle = new Rectangle(form.Left, form.Top, form.Width, form.Height); 

   // Test
   return Screen.AllScreens.Any(s => s.WorkingArea.IntersectsWith(formRectangle));
}

Solution 3:

Complete solution here (based on all answers). I have added a parameter MinPercentOnScreen where at least this % of pixels must be visible across all screens/displays. So if this returns false you will need to move the window's position back to default.

// Return True if a certain percent of a rectangle is shown across the total screen area of all monitors, otherwise return False.
public bool IsOnScreen(System.Drawing.Point RecLocation, System.Drawing.Size RecSize, double MinPercentOnScreen = 0.2)
{
    double PixelsVisible = 0;
    System.Drawing.Rectangle Rec = new System.Drawing.Rectangle(RecLocation, RecSize);

    foreach (Screen Scrn in Screen.AllScreens)
    {
        System.Drawing.Rectangle r = System.Drawing.Rectangle.Intersect(Rec, Scrn.WorkingArea);
        // intersect rectangle with screen
        if (r.Width != 0 & r.Height != 0)
        {
            PixelsVisible += (r.Width * r.Height);
            // tally visible pixels
        }
    }
    return PixelsVisible >= (Rec.Width * Rec.Height) * MinPercentOnScreen;
}

Implementation:

return IsOnScreen(this.Location, this.Size);