how to display ASPxGridView in usercontrol from another page

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DevExpress

ASP.NET4

i created a user control contain aspxgridview and page contain this user control and button when i click on the button in the page i pass values to methods in my user control
this code in the page pass values to method in user control

protected void ASPxButton1_Click(object sender, EventArgs e)
        {
            DisplayAttachmentControl d = new DisplayAttachmentControl();
            d.DisplayData(5, null);
        }

this is the method in my user control

public void DisplayData(int? documentId, int? ticketId)
        {
            Attachments attachment = new Attachments();
            dt = attachment.GetAttachmentByDocumentIDorTicketID(documentId, null);

            ASPxGridView1.DataSource = dt;
            ASPxGridView1.DataBind();
        }

the problem is when i pass datatable to aspxgridview1 this error appear

Quote:

System.NullReferenceException: Object reference not set to an instance of an object.

because aspxgridview1 is null how can i fix that ?