Making a draggable titlewindow without PopupManager

I wanted to make a application with a Windows-like interface with multiple draggable windows. TitleWindow was the obvious choice for the windows but they are only draggable only when created as a popup by the PopupManager.

I didn't want to use TitleWindow+PopupManager because I wanted to reserve PopupManager to display real popups that will always be on top of other components. Basically I wanted the windows to not be children of the systemManager but of a particular Canvas. This also means that I could have multiple "desktops" in the future.

To do this, first I created an extension of TitleWindow to make it draggable without being a popup.

DragWindow.as

package
{
 import flash.events.MouseEvent;
 import mx.containers.TitleWindow;

 public class DragWindow extends TitleWindow
 {
  public function DragWindow()
  {
  super();
  }

  override protected function createChildren():void
  {
   super.createChildren();
   this.titleBar.addEventListener( MouseEvent.MOUSE_DOWN, startDragging );
  }
 }
}

Then I created a WindowManager that replicates the behaviour of the PopupManager.

WindowManager.as

package
{
 import flash.display.DisplayObject;
 import flash.display.DisplayObjectContainer;
 import flash.events.MouseEvent;
 
 import mx.containers.Panel;
 import mx.containers.TitleWindow;
 import mx.core.IFlexDisplayObject;
 import mx.events.CloseEvent;
 
 public class WindowManager
 {
  // array of all windows in any container
  public static var windowList:Array = [];

  private static var instance:WindowManager;

  public function WindowManager():void
  {
   
  }

  public static function getInstance():WindowManager
  {
   if(instance == null)
   {
    WindowManager.instance = new WindowManager;
   }
   return WindowManager.instance;
  }

  public static function addWindow(window:IFlexDisplayObject, parent:DisplayObjectContainer):void
  {
   if(window is TitleWindow)
   {
    TitleWindow(window).showCloseButton = true;
    window.addEventListener(CloseEvent.CLOSE, WindowManager.closeWindow);
   }
   window.addEventListener(MouseEvent.MOUSE_DOWN, WindowManager.focusWindow);
   parent.addChild(DisplayObject(window));
   windowList.push(window);
  }

  // Brings the window to the top of displaylist of the parent
  public static function bringToFront(window:DisplayObject):void
  {
   var parent:DisplayObjectContainer = DisplayObjectContainer(window.parent);
   parent.setChildIndex( window, parent.numChildren - 1);
  }

  public static function createWindow(parent:DisplayObjectContainer, className:Class):IFlexDisplayObject
  {
   var window:IFlexDisplayObject = new className();
   WindowManager.addWindow(window, parent);

   return window;
  }

  public static function removeWindow(window:IFlexDisplayObject):void
  {
   var parent:DisplayObjectContainer = DisplayObjectContainer(window.parent);
   // Remove from display list
   parent.removeChild(DisplayObject(window));
   // Remove from window list
   windowList.splice(windowList.indexOf(window),1);
  }

  // Brings the window to the top of displaylist of the parent
  private static function focusWindow(event:MouseEvent):void
  {
   var window:DisplayObjectContainer = DisplayObjectContainer(event.currentTarget);
   WindowManager.bringToFront(window);
  }

  // Removes the window from the displaylist
  private static function closeWindow(event:CloseEvent):void
  {
   var window:IFlexDisplayObject = IFlexDisplayObject(event.currentTarget);
   WindowManager.removeWindow(window);
  }
 }
}

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