How can I transfer data from data grid view to datatable?

I am trying to get the string text out of a data grid view and store it in a data table so i can save the data table to a csv file. Problem is when I debug I notice the datatable stays null no matter what I do. I've tried everything. Does anyone know what I might be doing wrong and how I can fix it? Could it be something is wrong in the data source. It's saying it's null in the debugger as well.

public frmSettings()
{            
    InitializeComponent();
    lblMessage.Text = "Please create or open a setting file.";
    _dt = (DataTable)gvSettings.DataSource;
}         

private void mmuSaveAs_Click(object sender, EventArgs e)
{
            Cursor = Cursors.WaitCursor;
            saveFD.FileName = FileName;

            //FD means File Dialog    
            saveFD.Title = "Save a CSV File as desired.";
            saveFD.Filter = "CSV|*.csv";
            saveFD.FileName = "default";
            txtFilePath.Text = openFD.FileName;

            if (saveFD.ShowDialog(this) == DialogResult.OK)
                _dt = _objSetting.ProcessSettingFileCMD(saveFD.FileName);
}