取得值赋值给searchLookUpEdit没

取得值赋值给searchLookUpEdit没有
this.searchLookUpEdit_apr.Properties.DataSource = GetZgxxdb.GetYgglData();
            this.searchLookUpEdit_apr.Properties.DisplayMember = "zgxm";
            this.searchLookUpEdit_apr.Properties.ValueMember = "zggh";

apr  = this.dgv.CurrentRow.Cells["apr"].Value.ToString();

this.searchLookUpEdit_apr.Text = apr;
                this.textBox3.Text = apr;
怎么在searchLookUpEdit没有值显示
但实际apr是有值的。textbox框有显示


------解决思路----------------------
Properties.NullText="";