C# Change a SQL query and a Form1's DGV from another Form2

Question

I'm wondering what's the best way to change a variable from one Form to another.

I have in Form1 a datagridview that is updated by a sql query and listbox controls. So, when I select items in my From1's listboxes, it changes the sql query that will update the DGV:

public void Defaultview()
    {
        string strSQL = "SELECT mycolumn1, mycolumn2 FROM myTable";
        string strWhere;
        string connetionString = @"Data Source=mydatasource;Initial Catalog=myDB;Integrated Security=SSPI";            
        strWhere = GetListFilter(tableLayoutPanelForm1);
            if (strWhere != null)
            {
                strSQL += " WHERE " + strWhere;
            }
        SqlConnection cnn = new SqlConnection(connetionString);
        SqlDataAdapter adapter= new SqlDataAdapter(strSQL, cnn);
        DataTable Dt = DataTable();
        adapter.Fill(Dt);
        dataGridView1.DataSource = Dt;
    }

GetListFilter function will loop through all my listboxes and update the strWhere in function of the selectedItems from the listboxes.

  public string GetListFilter(Control ctrlContainer)
    {
        string strWhere = null;

        foreach (Control ctrl in ctrlContainer.Controls)
        {
            string strCondition = null;
            // ListBox handling
            if (ctrl.GetType() == typeof(ListBox) && ctrl.Name.Contains("CFRA") == true)
            {
                ListBox lb = ctrl as ListBox;

                foreach (var li in lb.SelectedItems)
                {

                    strCondition += $"'{li}',";

                }
                if (strCondition != null)
                {
                    if (strWhere == null)
                    {
                        strCondition = strCondition.TrimEnd(',');
                        strWhere += $"{ctrl.Name.Substring(13)} IN ({strCondition})";
                    }
                    else if (strWhere != null)
                    {
                        strCondition = strCondition.TrimEnd(',');
                        strWhere += $" AND {ctrl.Name.Substring(13)} IN ({strCondition})";
                    }
                }
            }

        }
        return strWhere;
    }

Ok, now I click on a button1 from this Form1 and make a Form2 appears:

private void btn1(object sender, EventArgs e)
    {
        var Form2 = new Form2(this);
        Form2.Show();
        Form2.TopMost = true;
    }

Within this form2, I have two listboxes that I can drag and drop value from the first one to the other. Then I have a button2 in this Form2 and when I click on it, I need to have my strSQL variable (from Form1) changed so that my DatagridView in Form1 can display the right infos.

So my question is: At the end, only the string "strWhere" need to be updated with Form2's listbox selection so should I update my Form1's sql query from Form2? Or maybe create a new datatable in Form2 that I send to my DGV in form1? Or simply create a new instance of my Form1 when I click on the button of my Form2 but in this case, how can I take into acccount the new selection of my Form2... I'm a bit confused on how to proceed on this one... Any suggestion would be nice

Answer 1

If I understand correctly, I think you need something like this at some point in Form2:

    Form1 form1;
    form1 = (Form1)Application.OpenForms["Form1"];
    if (form1 != null)
    {
        form1.UpdateStuff(var someParam);
    }

So, your Form1 is located in the application and then you invoke a public method (UpdateStuff) to do what you need.