c#实现打印预览和打印【打印的位置不准确】

//http://dotnet.chinaitlab.com/List_233.html
private void button4_Click(object sender, EventArgs e)
{

//预览功能,需要增加一个控件: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)
{
//打印功能,需要增加一个控件:printDialog
printDialog1.Document = ThePrintDocument;
string strText = richTextBox1.Text;
StringReader myReader = new StringReader(strText);
if (printDialog1.ShowDialog() == DialogResult.OK)
{
//这个方法将调用ThePrintDocument_PrintPage事件完成打印任务
ThePrintDocument.Print();
}
}

private void ThePrintDocument_PrintPage(object sender, PrintPageEventArgs ev)
{
//真正打印功能的实现
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);

//计算每一页打印多少行
linesPerPage = ev.MarginBounds.Height / printFont.GetHeight(ev.Graphics);

//重复使用StringReader对象　,打印出richTextBox1中的所有内容
while (count < linesPerPage && ((line = myReader.ReadLine()) != null))
{
//　计算出要打印的下一行所基于页面的位置
yPosition = topMargin + (count * printFont.GetHeight(ev.Graphics));
//　打印出richTextBox1中的下一行内容
ev.Graphics.DrawString(line, printFont, myBrush, leftMargin, yPosition, new StringFormat());
count++;
}
//　判断如果还要下一页，则继续打印
if (line != null)
ev.HasMorePages = true;
else
ev.HasMorePages = false;
myBrush.Dispose();
}