User Controls :: How To Pass Value From UserControl (ASCX) To Page (ASPX)

I have two files in my project. One is user control (popup) customerpicker.ascx and one is default.aspx page. In customerpicker I have dynamically generated gridview and 'select' column with SelectButton.

What I want is this: When I click on 'select' on random row in gridview, then I like to display value from selected row immediately (like ajax) to aspx.page. How it is possible?

There is part of my code in .ascx:

public string showOnaspx { get; set; }
protected void GridView1_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
{
GridViewRow row = GridView1.Rows[e.NewSelectedIndex];
showOnaspx = row.Cells[1].Text;
e.Cancel = true;
}
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
GridViewRow row = GridView1.SelectedRow; 
//row[i].Attributes.Add("onclick", "$('#ContentIndex_sometextbox).val(" + row[i].Cells[1].Text// + "); $('#Close').click();");
}

I also tried with jqeury (comment in selectedindexchanged function), but it does not work well, because user have to click SELECT two times to effect.