How scroll a canvas up? (Writing chat in Flex)

Question

I'm writing a chat client using Flex.

The basis for the chat window is a canvas. I've got that showing, but how do I make it scroll up? I want to clip the window so only the last 15 lines are shown.

This doesn't appear to be working (nothing moves):

<mx:Canvas id="canvas" width="300" height="3000" horizontalScrollPolicy="off" verticalScrollPolicy="on" creationComplete="myinit()">
    <mx:Label text="HI" x="10" y="100"/>
</mx:Canvas>

Shouldn't this scroll the canvas every time it's called?:

canvas.verticalScrollPosition += 10;

Answer 1

You should change the verticalScrollPosition of the parent container. Such as

<mx:Canvas id="canvas" width="300" height="300"
           horizontalScrollPolicy="off" verticalScrollPolicy="on"
           creationComplete="myinit()">
    <mx:Canvas id="canvas" width="300" height="3000">
        <mx:Label text="HI" x="10" y="100"/>
    </mx:Canvas>
</mx:Canvas>

Now

canvas.verticalScrollPosition += 10;

should work.