如果gridview导出excel文件时，这个文件名是存在且处于打开状态时怎么处理？
下面是一段excel导出的程序：
private void buttonExcle_Click(object sender, EventArgs e)
{
SaveFileDialog saveFileDialog = new SaveFileDialog();
DfWeb web = new DfWeb(new P101001Service(), this);
P101001DataSet dset = (P101001DataSet)web.Execute("GetDayListBySearch");
_griddata = dset.DayList;
dfDataGridView1.DataSource = _griddata;

saveFileDialog.Filter = "Execl files (*.xls)|*.xls";

saveFileDialog.FilterIndex = 0;

saveFileDialog.RestoreDirectory = true;

saveFileDialog.CreatePrompt = true;

saveFileDialog.Title = "Export Excel File To";
if (saveFileDialog.ShowDialog() == DialogResult.Cancel)
{
return;
}
Stream myStream;

myStream = saveFileDialog.OpenFile();

StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding("gb2312"));

StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding(-0));

string str = "";
try
{
for (int i = 0; i < dfDataGridView1.ColumnCount; i++)
{
if (i > 0)
{

str += "\t";

}
str += dfDataGridView1.Columns[i].HeaderText;

}
sw.WriteLine(str);

写内容

for (int j = 0; j < dfDataGridView1.Rows.Count; j++)
{

string tempStr = "";

for (int k = 0; k < dfDataGridView1.Columns.Count; k++)
{
if (k > 0)
{
tempStr += "\t";
}
object value = dfDataGridView1.Rows[j].Cells[k].Value;
if (value == null)
{
value = string.Empty;
}
tempStr += value.ToString();

}
sw.WriteLine(tempStr);
}

sw.Close();
myStream.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());

}
finally
{
sw.Close();
myStream.Close();
}
}
如果gridview导出excel文件时，这个文件名是存在且处于打开状态时怎么处理？如果不处理，程序将会崩溃。
求各位大侠鼎力帮助。

[解决办法]
你将if (saveFileDialog.ShowDialog() == DialogResult.Cancel)
{
return;
}
Stream myStream;

myStream = saveFileDialog.OpenFile();

StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding("gb2312"));

StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding(-0));

写到try里面，捕获异常，然后抛出即可。