How to fill dropdownlist in EditItemTemplate of asp.net ListView control

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C#

ASP.NET

ListView

I want to fill a DropDownList in my ListView EditItemTemplate when Edit is activated. I tried this code. But, The EditItem is null, and it throws a NullReferenceException.

protected void ListView3_ItemEditing(object sender, ListViewEditEventArgs e)
    {
        if (e.NewEditIndex >= 0 && ListView3.Items[e.NewEditIndex].ItemType == ListViewItemType.DataItem)
        {
            object _edSubPro = ListView3.EditItem.FindControl("edListSubProject");
            if (_edSubPro != null && _edSubPro is DropDownList)
            {
                DropDownList _edSubProDP = (DropDownList)_edSubPro;
                BindDropDownList(_edSubProDP, "select  SubProjectID, (LEFT(SubProjectCode + REPLICATE(' ' , 7), 7) + ' | ' + SubProjectName) AS SubProjectName  from SubProject", "SubProject", "SubProjectName", "SubProjectID");
            }
        }
    }