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Adobe Flex/AIR: Scrolling a sub-component, not the whole window

Answer 1

+1 A:

Found a solution.

Looks like the only way to prevent the VBox from aggressively extending its vertical space (and forcing its parents to grow scrollbars) is to wrap the VBox in a Canvas.

There's a handy little component here, called ScrollableVBox, which performs the workaround while taking care of a few bookkeping issues (like adding and removing children to the VBox, passing them around the Cavas wrapper).

benjismith 2008-12-10 12:24:19

Answer 2

A:

Your problem seems like a lot like one that I struggled with some time ago. I found my answer from this discussion: just disable the measure() implementation of the Box.

This was a pretty easy fix which worked perfectly in my case and hasn't caused any "collateral damage". Your results may vary.

package whatever
{
    import mx.containers.Box;

    /**
    * A Box that has no measure() implementation.
    * 
    * <p>
    * See <a href="http://tinyurl.com/2hvmav"&gt;here&lt;/a&gt; for more info.
    * </p>
    */
    public class NonMeasuredBox extends Box
    {
        /**
        * Constructor
        */
        public function NonMeasuredBox():void
        {
            super();
        }

        override protected function measure():void { /* disabled */ }
    }
}

hasseg 2008-12-10 12:32:45

I'll give that a try later in the afternoon. I'd imagine, though, that disabling measure makes it difficult to provide horizontal resizing of the container. I just want to fix the vertical scrolling problem.

benjismith 2008-12-10 15:18:31

You're totally right -- this is a pretty drastic hack but might be useful in some specific situations (like mine.)

hasseg 2008-12-10 15:28:02

Answer 3

+4 A:

An HBox or a VBox will try as hard as possible to display its content without scroll bars. This forces a parent container (often all the way up to the main Application) to be the one that must scroll if the content is too large to fit in the available bounds.

Behind the scenes, the HBox or VBox is setting the measuredMinWidth and measuredMinHeight properties in its measure() function to match the dimensions required by its children. The parent container will honor that recommendation and the task of scrolling moves up the display list.

hasseg's solution works in many cases because it stops the container from measuring, but it's kind of hacky. Here's what you can do without building replacement subclasses for your containers. On the container instance that you want to scroll, set minWidth or minHeight to 0. This will take precedence over the measuredMinWidth or measuredMinHeight properties of that container, allowing the parent to set the actual size to something more manageable.

joshtynjala 2008-12-11 22:40:44

Answer 4

A:

It seems like giving fixed height or width in pixels (and not percentage!) to a given box will solve the problem without addition Canvas enclosure. However this only works if you know the size of the box in pixels, dynamic sized boxes still lack the ability of rendering properly.

ifroz 2010-01-17 15:37:13

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Adobe Flex/AIR: Scrolling a sub-component, not the whole window

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