Question

i have application with Listbox and files, each time i press on Add button the default C drive open and i want the application to remember the last path i used

private void btnAdd_Click(object sender, EventArgs e)
{
    System.IO.Stream myStream;
    OpenFileDialog thisDialog = new OpenFileDialog();
    thisDialog.InitialDirectory = "c:\\";
    thisDialog.Filter = "(*.snoop, *.pcap, *.cap, *.net)|*.snoop; *.pcap; *.cap; *.net|" + "All files (*.*)|*.*";
    thisDialog.FilterIndex = 1;
    thisDialog.RestoreDirectory = false;
    thisDialog.Multiselect = true; // Allow the user to select multiple files
    thisDialog.Title = "Please Select Source File";
    thisDialog.FileName = lastPath;
    List<string> list = new List<string>();

    if (thisDialog.ShowDialog() == DialogResult.OK)
    {
        foreach (String file in thisDialog.FileNames)
        {
            try
            {
                if ((myStream = thisDialog.OpenFile()) != null)
                {
                    using (myStream)
                    {
                        listBoxFiles.Items.Add(file);
                    }
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
            }
        }

    }
}

Answer 1

Save the last directory used in a global variable like this:

private string _lastPath = string.Empty;

then after the file selection initialize it:

if(thisDialog.Filenames.Length > 0)
    _lastPath = Path.GetDirectoryName(thisDialog.Filenames[0]);

when you reopen the dialog set the InitialDirectory with this check:

thisDialog.InitialDirectory = (_lastPath.Length > 0 ? _lastPath: "c:\\"); 

and remove the thisDialog.FileName = lastPath;

EDIT — UPDATE OF YOUR CODE —

// This at the global level of your form 
private string _lastPath = string.Empty;**

private void btnAdd_Click(object sender, EventArgs e) 
{ 
    System.IO.Stream myStream; 
    OpenFileDialog thisDialog = new OpenFileDialog(); 
    thisDialog.InitialDirectory = (_lastPath.Length > 0 ? _lastPath: "c:\\");
    thisDialog.Filter = "(*.snoop, *.pcap, *.cap, *.net)|*.snoop; *.pcap; *.cap; *.net|" + "All files (*.*)|*.*"; 
    thisDialog.FilterIndex = 1; 
    thisDialog.RestoreDirectory = false; 
    thisDialog.Multiselect = true; // Allow the user to select multiple files 
    thisDialog.Title = "Please Select Source File"; 
    thisDialog.FileName = lastPath; 
    List<string> list = new List<string>(); 

    if (thisDialog.ShowDialog() == DialogResult.OK) 
    { 
        if(thisDialog.Filenames.Length > 0) 
            _lastPath = Path.GetDirectoryName(thisDialog.Filenames[0]);

        foreach (String file in thisDialog.FileNames) 
        { 
            try 
            { 
                if ((myStream = thisDialog.OpenFile()) != null) 
                { 
                    using (myStream) 
                    { 
                        listBoxFiles.Items.Add(file); 
                    } 
                } 
            } 

            catch (Exception ex) 
            { 
                MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message); 
            } 
        } 

    } 
}