c#實現預覽列印和列印【列印的位置不準確】

        //http://dotnet.chinaitlab.com/List_233.html
        private void button4_Click(object sender, EventArgs e)
        {
           
            //預覽功能,需要增加一個控制項:ThePrintDocument
            string strText = richTextBox1.Text;
            StringReader myReader = new StringReader(strText);
            PrintPreviewDialog printPreviewDialog1 = new PrintPreviewDialog();
            printPreviewDialog1.Document = ThePrintDocument;
            printPreviewDialog1.FormBorderStyle = FormBorderStyle.Fixed3D;
            printPreviewDialog1.ShowDialog();
        }

        private void button5_Click(object sender, EventArgs e)
        {
            //列印功能,需要增加一個控制項:printDialog
            printDialog1.Document = ThePrintDocument;
            string strText = richTextBox1.Text;
            StringReader myReader = new StringReader(strText);
            if (printDialog1.ShowDialog() == DialogResult.OK)
            {
                //這個方法將調用ThePrintDocument_PrintPage事件完成列印任務
                ThePrintDocument.Print();
            }
        }

        private void ThePrintDocument_PrintPage(object sender, PrintPageEventArgs ev)
        {
            //真正列印功能的實現
            string strText = richTextBox1.Text;
            StringReader myReader = new StringReader(strText);

            float linesPerPage = 0;
            float yPosition = 0;
            int count = 0;

            float leftMargin = ev.MarginBounds.Left;
            float topMargin = ev.MarginBounds.Top;
           
            string line = null;
            Font printFont = richTextBox1.Font;
            SolidBrush myBrush = new SolidBrush(Color.Black);
           
            //計算每一頁列印多少行
            linesPerPage = ev.MarginBounds.Height / printFont.GetHeight(ev.Graphics);
           
            //重複使用StringReader對象　,列印出richTextBox1中的所有內容
            while (count < linesPerPage && ((line = myReader.ReadLine()) != null))
            {
                //　計算出要列印的下一行所基於頁面的位置
                yPosition = topMargin + (count * printFont.GetHeight(ev.Graphics));
                //　列印出richTextBox1中的下一行內容
                ev.Graphics.DrawString(line, printFont, myBrush, leftMargin, yPosition, new StringFormat());
                count++;
            }
            //　判斷如果還要下一頁，則繼續列印
            if (line != null)
                ev.HasMorePages = true;
            else
                ev.HasMorePages = false;
            myBrush.Dispose();
        }