Opening, Reading, and Writing a file

Here is an example of Opening/Reading a file in btnOpen_Click and Writing in btnSave_Click:

    protected void btnOpen_Click(object sender, EventArgs e)
    {
        if (string.IsNullOrEmpty(txtFileName.Text)) txtFileName.Text="c:/temp/temp.txt";
        StreamReader sr = null;
        try
        {
            sr = new StreamReader(txtFileName.Text);
            txtFileContent.Text = sr.ReadToEnd();
            sr.Close();
            displayMessage("Successfully opened file");
        }
        catch (Exception ex)
        {
            displayMessage(ex.Message);
        }
        finally
        {
            sr.Close();
        }
    }
    protected void btnSave_Click(object sender, EventArgs e)
    {
        if (string.IsNullOrEmpty(txtFileName.Text)) txtFileName.Text = "c:/temp/temp.txt";
        StreamWriter sw = null;
        try{
            sw = new StreamWriter(txtFileName.Text);
            string[] ar;
            ar = txtFileContent.Text.Split(Environment.NewLine.ToCharArray());
            foreach (string sIn in ar)
            {
                if(!string.IsNullOrEmpty(sIn))
                    sw.Write(sIn.Trim()+Environment.NewLine);
            }
        }catch (Exception ex) 
        {
            displayMessageLine(ex.Message);
        }
        finally{
            sw.Close();
        }
    }