Form Location and Size behaviour

Question

I want to position Form on top left corner of the screen.

I have tried this.Location = new Point(0,0) but window is positioned at (7,0) - top of the window is on top of the screen but left side is 7 pixels from the screen edge. I created new WinForms app for testing and added only this code:

private void Form1_Load(object sender, EventArgs e)
{
    Point p = new Point(0, 0);

    WindowState = FormWindowState.Maximized;
    Debug.WriteLine("\nMaximized");
    Debug.WriteLine("Location: " + Location);
    Debug.WriteLine("Size: " + Size);
    Debug.WriteLine("PointToScreen(0,0): " + PointToScreen(p));

    WindowState = FormWindowState.Normal;
    Location = p;            
    Debug.WriteLine("\nNormal");
    Debug.WriteLine("Location: " + Location);
    Debug.WriteLine("Size: " + Size);
    Debug.WriteLine("PointToScreen(0,0): " + PointToScreen(p));

    Debug.Write("\nScreen.PrimaryScreen.WorkingArea: ");
    Debug.WriteLine(Screen.PrimaryScreen.WorkingArea);
}

The output is:

Maximized  
Location: {X=-8,Y=-8}  
Size: {Width=1936, Height=1056}
PointToScreen(0,0): {X=0,Y=23}

Normal
Location: {X=0,Y=0}
Size: {Width=300, Height=300}
PointToScreen(0,0): {X=8,Y=31}

Screen.PrimaryScreen.WorkingArea: {X=0,Y=0,Width=1920,Height=1040}

Why Location = new Point(0,0) doesn't position form on (0,0)? Is this due to something on my system? I have Win10 and VS2015. Taskbar is on the bottom, there is nothing on the left side of my desktop. In order to position it on (0,0) I actually have to position it on (-7,0). Also, reported width of the maximized form is 16 pixels larger than screen width. I understand that because of window edges, title bar etc there is a difference between client area size and form size, but this is not it. When the form is maximized there are no left and right edges (client area width = desktop width) but form width is +16px. There is +8px on each of the 4 sides of the form but Y position is OK. Why is Y-position OK and X is not?

Answer 1

Thanks to Uwe Keim and his own answer to his question, I've created MoveForm function that calculates offset and sets location of the form correctly, regardless of Windows version (ie border size):

    void MoveForm(Point p)   // Move form to point 'p'
    {
        this.WindowState = FormWindowState.Normal;
        this.Location = new Point(0, 0);
        Rectangle rec = WindowHelper.GetWindowRectangle(this.Handle);
        p.Offset(-rec.Location.X, -rec.Location.Y);
        this.Location = p;
    }

MoveForm function uses WindowHelper class from Uwe Keim's post:

public static class WindowHelper
{
    // https://code.google.com/p/zscreen/source/browse/trunk/ZScreenLib/Global/GraphicsCore.cs?r=1349

    /// <summary>
    /// Get real window size, no matter whether Win XP, Win Vista, 7 or 8.
    /// </summary>
    public static Rectangle GetWindowRectangle(IntPtr handle)
    {
        if (Environment.OSVersion.Version.Major < 6)
        {
            return GetWindowRect(handle);
        }
        else
        {
            Rectangle rectangle;
            return DWMWA_EXTENDED_FRAME_BOUNDS(handle, out rectangle) ? rectangle : GetWindowRect(handle);
        }
    }

    [DllImport(@"dwmapi.dll")]
    private static extern int DwmGetWindowAttribute(IntPtr hwnd, int dwAttribute, out Rect pvAttribute, int cbAttribute);

    private enum Dwmwindowattribute
    {
        DwmwaExtendedFrameBounds = 9
    }

    [Serializable, StructLayout(LayoutKind.Sequential)]
    private struct Rect
    {
        // ReSharper disable MemberCanBePrivate.Local
        // ReSharper disable FieldCanBeMadeReadOnly.Local
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
        // ReSharper restore FieldCanBeMadeReadOnly.Local
        // ReSharper restore MemberCanBePrivate.Local

        public Rectangle ToRectangle()
        {
            return Rectangle.FromLTRB(Left, Top, Right, Bottom);
        }
    }

    private static bool DWMWA_EXTENDED_FRAME_BOUNDS(IntPtr handle, out Rectangle rectangle)
    {
        Rect rect;
        var result = DwmGetWindowAttribute(handle, (int)Dwmwindowattribute.DwmwaExtendedFrameBounds,
            out rect, Marshal.SizeOf(typeof(Rect)));
        rectangle = rect.ToRectangle();
        return result >= 0;
    }

    [DllImport(@"user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool GetWindowRect(IntPtr hWnd, out Rect lpRect);

    private static Rectangle GetWindowRect(IntPtr handle)
    {
        Rect rect;
        GetWindowRect(handle, out rect);
        return rect.ToRectangle();
    }
}

Answer 2

I figured out the problem.

Just set

this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;

and test the result. for me it is this:

Maximized
Location: {X=0,Y=0}
Size: {Width=1280, Height=800}
PointToScreen(0,0): {X=0,Y=0}

Normal
Location: {X=0,Y=0}
Size: {Width=477, Height=321}
PointToScreen(0,0): {X=0,Y=0}

It is all about the border.