正确计算String长度

        [DllImport("gdi32")]
        private static extern bool GetTextExtentPoint32(IntPtr hdc, string lpString, int cbString, out Size lpSize);
        [DllImport("gdi32")]
        private static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
        [DllImport("gdi32")]
        private static extern IntPtr DeleteObject(IntPtr hDC);
        static Size MeasureTextWidth(Graphics graphics, string text, Font textFont)
        {
            IntPtr hdc = graphics.GetHdc();
            IntPtr hFont = textFont.ToHfont();
            SelectObject(hdc, hFont);
            Size size = new Size();
            GetTextExtentPoint32(hdc, text, text.Length, out size);
            graphics.ReleaseHdc();
            DeleteObject(hFont);
            return size;
        }