row filter to dataview in wpf not working

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WPF

string s1 = "";
           string s= ((ComboBoxItem)cmbSearchBy.SelectedItem).Content.ToString() ;
          if (cmbSelect.SelectedValue != null)
          {
                 s1 =  (cmbSelect.SelectedValue).ToString();
          }
        dv = new DataView(dt);
        dv.RowFilter = "'" + s.Trim() + "'='" + s1.Trim() +"'";
       dt = new DataTable();
       dt = dv.ToTable();

this is my code where i want to filter record, using condition
but here it is not working

here in cmbsearchby i t select the column name and in cmbselect i select value, but it does not showing any record