Question

There is a <mx:ComboBox> component with prompt = 'Please Select'. User selects an option, save it, comes back tomorrow and want to undo it. How would he do that? Because prompt option is gone now.

Just to mention

I am populating ComboBox values from database and there are thousands
of comboBoxes in my application.

Answer 1

If combobox is closed without selection being made, prompt will reappear automatically.

If an item has been selected, just do:

myCombobox.selectedIndex = -1;

To remove selection and prompt will reappear

Edit after question revised:

Use a button to clear selection:

<s:Button label="clear" click="myCombobox.selectedIndex=-1" />

Or multiple clears:

<s:Button label="clear" click="clearCombos()" />

function clearCombos():void
{
    myCombobox1.selectedIndex = -1;
    myCombobox2.selectedIndex = -1;
    // etc...
}