Get DataTable from DataGridView

I have one form that is a CRUD, this form can manage any data from many tables, if a table has foreign keys the CRUD found the tables and columns for respectives columns of the current table, so in the DataGridView can show columns as CheckBox, TextBox or ComboBox

I do all this BEFORE the DataGridView is filled with the data, so I can't use this:

dataGridView1.DataSource = dtCurrent;

I need something like this:

dtCurrent = dataGridView1.DataSource;

But just give a null

I have tried with ExtensionMethod to the DataGridView:

public static DataTable ToDataTable(this DataGridView dataGridView, string tableName)
{

    DataGridView dgv = dataGridView;
    DataTable table = new DataTable(tableName);

    // Crea las columnas 
    for (int iCol = 0; iCol < dgv.Columns.Count; iCol++)
    {
        table.Columns.Add(dgv.Columns[iCol].Name);
    }

    /**
      * THIS DOES NOT WORK
      */
    // Agrega las filas 
    /*for (int i = 0; i < dgv.Rows.Count; i++)
    {
        // Obtiene el DataBound de la fila y copia los valores de la fila 
        DataRowView boundRow = (DataRowView)dgv.Rows[i].DataBoundItem;
        var cells = new object[boundRow.Row.ItemArray.Length];
        for (int iCol = 0; iCol < boundRow.Row.ItemArray.Length; iCol++)
        {
            cells[iCol] = boundRow.Row.ItemArray[iCol];
        }

        // Agrega la fila clonada                 
        table.Rows.Add(cells);
    }*/

    /* THIS WORKS BUT... */
    foreach (DataGridViewRow row in dgv.Rows)
    {

        DataRow datarw = table.NewRow();

        for (int iCol = 0; iCol < dgv.Columns.Count; iCol++)
        {
            datarw[iCol] = row.Cells[iCol].Value;
        }

        table.Rows.Add(datarw);
    }

    return table;
} 

I use:

dtCurrent = dataGridView1.ToDataTable(dtCurrent.TableName);

The code do