Ans:

The singleton pattern is a design pattern that is used to restrict instantiation of a class to one object. If you create the class as a singleton then no way to create more than one instance. But, you can get that single instance in any number of classes. So all the classes will share the same properties and behaviours of that singleton object.

For example:

<SettingsDialog xmlns:mx="http://www.adobe.com/2006/mxml">

    <mx:Script>

        private static var singleton:SettingDialog;

        public static function getInstance():SettingsDialog
        {
            if ( SettingsDialog.singleton )
            {
                return SettingsDialog.singleton;
            }else{
                SettingsDialog.singleton = new SettingsDialog();
                return SettingsDialog.singleton;
            }            
        }

    </mx:Script>

    <mx:TextInput id="name" width="100">
    <mx:TextInput id="age" width="100">
    <mx:TextInput id="rank" width="100">
    <mx:TextInput id="serial" width="100">
    <mx:ColorPicker id="uiColor" >

<SettingsDialog>


Usage:
//call popupmanager with getInstance
mx.managers.PopUpManager.addPopUp( SettingsDialog.getInstance() , basePanel , true );