How to assign combobox selected value to textbox on the same form ?

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C#

i want to assign combobox selected value to textbox. where my combobox fetching values from database on another combobox selected index change event.

here is my code.

private void cboRNum_SelectedIndexChanged(object sender, EventArgs e)
       {
           txtRoomIndex.Text = cboRNum.SelectedValue.ToString();
       }

text box shows "System.Data.DataRowView" instead of displaying actual selected value.