R – Flex 3 focusManager.getNextFocusManagerComponent() returns null

"I've tried overriding the updateDisplayList() method of the mx:Canvas component but that seems to only update the drawing after the dragging. I would like for the line to follow the mx:Panel as it is being dragged."

You can listen to MoveEvent.MOVE events in the Panels and have the handler call for the redrawing of the lines, and then have the Panels dispatch these events while they are being dragged by listening for MouseEvent.MOUSE_MOVE events in the stage and dispatching the MOVE event in the handler (attach this handler to the stage in the Panel's MouseEvent.MOUSE_DOWN event handler, along with a handler for MouseEvent.MOUSE_UP (attached to the stage as well) -- then remove both of these event listeners from the stage in the MOUSE_UP handler.)

Here's an example (this would be in the Panel subclass:)

private function attachListeners():void
{
    this.addEventListener(MouseEvent.MOUSE_DOWN, selfMouseDownHandler, false,0,true);
    this.addEventListener(MoveEvent.MOVE, selfMoveHandler, false,0,true);
}

private function selfMoveHandler(event:MoveEvent):void
{
    redrawConnectedLinks();
}

private function selfMouseDownHandler(event:MouseEvent):void
{
    stage.addEventListener(MouseEvent.MOUSE_UP, stageMouseUpHandler, false,0,true);
    stage.addEventListener(MouseEvent.MOUSE_MOVE, stageMouseMoveHandler, false,0,true);
}

private function stageMouseUpHandler(event:MouseEvent):void
{
    stage.removeEventListener(MouseEvent.MOUSE_UP, stageMouseUpHandler, false);
    stage.removeEventListener(MouseEvent.MOUSE_MOVE, stageMouseMoveHandler, false);
}

private function stageMouseMoveHandler(event:MouseEvent):void
{
    dispatchEvent(new MoveEvent(MoveEvent.MOVE));
}

I would approach this by extending the Alert class to include functionality that listens for keyUp events from the Enter and Space keys.

In the createChildren method of your subclass:

override public function createChildren():void
{
    super.createChildren();
    this.addEventListener(KeyboardEvent.KEY_UP, keyUpListener);
    this.stage.addEventListener(KeyboardEvent.KEY_UP, keyUpListener);
}

private function keyUpListener(e:KeyboardEvent):void
{
    if(e.keyCode == Keyboard.ENTER || e.keyCode == Keyboard.SPACE)
    {
        //Trigger the Alert.YES functionality...
    }
}

I'm having some issues with my set up this morning and can't get into the Alert class to provide info on how to "Trigger the Alert.YES functionality", but I'll try to post some more on this later on. Hope this little bit helps.

Also - I'm not 100% on this - but I think you will need to manually remove the event listeners when the Alert popup is removed.

Aaand... you may not need both of those listeners. Can't test right now to make sure.

UPDATE: -----------------

After a little more looking, maybe the best way to go about this is to extend the AlertForm class (which manages the Alert's buttons), and then extend the Alert class to use your extended AlertForm class.

The AlertForm class has a keyDownHandler method, which it defines like this:

override protected function keyDownHandler(event:KeyboardEvent):void
{
    var buttonFlags:uint = Alert(parent).buttonFlags;

    if (event.keyCode == Keyboard.ESCAPE)
    {
        if ((buttonFlags & Alert.CANCEL) || !(buttonFlags & Alert.NO))
            removeAlert("CANCEL");
        else if (buttonFlags & Alert.NO)
            removeAlert("NO");
    }
}

You can see that it is setting up the 'close' behavior in response to pressing the Escape key. You add a little logic, based on the code in the above 'keyUpListener' function to make a call to the AlertForm's removeAlert method, passing in the appropriate String value for the Yes button.

For reference, the removeAlert method looks like this:

private function removeAlert(buttonPressed:String):void
{
    var alert:Alert = Alert(parent);

    alert.visible = false;

    var closeEvent:CloseEvent = new CloseEvent(CloseEvent.CLOSE);
    if (buttonPressed == "YES")
        closeEvent.detail = Alert.YES;
    else if (buttonPressed == "NO")
        closeEvent.detail = Alert.NO;
    else if (buttonPressed == "OK")
        closeEvent.detail = Alert.OK;
    else if (buttonPressed == "CANCEL")
        closeEvent.detail = Alert.CANCEL;
    alert.dispatchEvent(closeEvent);

    mx.managers.PopUpManager.removePopUp(alert);

}