Correct VALIDATING event statement for a COMBOBOX

Question

I would like to know what can i do to construct a correct statement using the VALIDATING method for a COMBOBOX. I would like to see an example of a statement. My code below had an error and i dont know how to solve them. "this.cboTipoentrada.Validating += new System.EventHandler (this.perdefocoentrada);" System.EventHandler is wrong. Whats the correct word?