为何打印之前要多余的去测量字体大小

为什么打印之前要多余的去测量字体大小?

C# code

            Font titleFont = new Font("宋体", 12);            SizeF titleSize = e.Graphics.MeasureString("计划单", titleFont);//测量字体大小            X = (e.PageBounds.Width - titleSize.Width) / 2;            e.Graphics.DrawString("计划单", titleFont, Brushes.Black, X, Y);//画标题            Y += titleSize.Height + 15;            X = e.PageBounds.Width * 0.05f;            titleFont.Dispose();