How to Prevent users from entering values that do not exist in the ComboBox control data source list

Add a validating event to combbox, Code As follows: // If the input value does not exist in commbobox, select the first item. If the list is empty, clear the input.
// Usage: Add the following line of code to the validating event of ComboBox:
// Commonfunctions. comboboxselectonly (ComboBox) sender );
Public   Static   Void Comboboxselectonly (ComboBox CMBX ){
If (CMBX. selectedindex = CMBX. findstringexact (CMBX. Text )) =   - 1 ){
CMBX. Text =   "" ;
}
}