Contact envelope



Scroller class that extends the Flex SDK Scroller and adds support for smooth mouse wheel scrolling, as well as granular control over the number of pixels scrolled for mouse wheel and stepping actions via both the mouse and keyboard.

The Flex SDK Scroller makes control over the number of pixels scrolled difficult by requiring the developer to extend the viewport/layout to change the default scroll amount from 1 pixel. The SDK is also vague on the mouse event "delta" property that can wildly fluctuate the amount of scroll on each mouse wheel tick, and is user OS dependent.

This class is an attempt to solve these deficiencies.

Creating the Scroller

The component extends Scroller, so the Ardisia Scroller can be added to any container that supports a Scroller.

Using the Scroller

The Scroller adds two general improvements: (A) the ability to smooth scroll mouse wheel scrolling, and (B) control over the number of pixels to scroll for the mouse wheel, keyboard arrow keys, and clicking the increment/decrement buttons on the scrollbars. Currently, the Flex SDK Scroller lacks this functionality and retrieves the scroll amounts from the viewport and layout, which forces extending the layout for every custom use of a scroller.

To set the mouse wheel scroll amount per tick, set the "mouseWheelStepSize" property. To set the scroll amount for keyboard arrow keys and the increment/decrement buttons on the scrollbars, use the "scrollStepSize" property.

To fallback to retrieving scroll values from the viewport and layout (like the Flex SDK Scroller), set the "mouseWheelStepSize", "mouseWheelEventDelta", and "scrollStepSize" to 0. If these properties are 0, this class will act just like the SDK Scroller except with mouse wheel animation support via the "smoothScrolling" style.

By default, the Scroller does NOT accept focus, which means to enable keyboard support for scrolling, "focusEnabled" must be set to true. Keys supported are: arrow keys, page up, page down, home, end.

The VScrollBar and HScrollBar classes are designed to be initialized and parented by this class. Do not use them independently of the Scroller class.

Mouse wheel scrolling is also affected by the "delta" property on mouse wheel events. The "delta" property affects wheel scrolling by multiplying the scroll amount by the delta value. The delta value is somewhat specific to the user's OS/Browser and may accelerate scrolling. For example, possible acceleration may occur if the user keeps scrolling after an initial flick of the mouse wheel. The OS may determine that the user is trying to traverse a large list and provide increasing multiples of This could be considered a good thing, but it can lead to frustration when a developer is trying to exert rigid control over the amount of scroll per wheel tick.

The Scroller can control this value directly via the "mouseWheelEventDelta" property. Set the "mouseWheelEventDelta" property to 1 to effectively ignore the "delta" property altogether. Set to "0" to use the delta returned by the flash player.

Notes on Event Handling and the Flex SDK Scroller and HScrollBar/VScrollBar classes.

The Scroller and the H/VScrollBars work in tandem because both listen to property changes on the viewport. Therefore, if either change the viewport's scroll positions, both the Scroller and H/VScrollBar will update. This allows for some redundancy. For example, both have MouseWheelEvent listeners attached to (A) the skin for the Scroller, and (B) the viewport for the H/VScrollBar. More on this below.

Both call the viewport for the number of pixels to change the scroll in response to user interaction. The viewport will then call a function on the associated layout for the pixel delta to apply.

Despite the redundancy between the classes, the Scroller is primarily responsible for touch scrolling and all of the keyboard interaction, and the H/VScrollBar classes handle mouse interaction and animations.

Regarding animations, the H/VScrollBars have support for animation built in, but they choose to ignore it for single step operations. Animation support does exist for repeated stepping (holding down the increment button), paging, and jumping to a position on the scrollbar. The animations are so fast using the default "repeatInterval" and "repeastDelay" styles that it is easy to not notice that they are animated at all. Despite having animation support built in, it is very hard to customize because nearly all of the animation code is private. The H/VScrollBar handles the animations alone without any interaction from the Scroller. In fact, the Scroller does not support any animation.

Both the Scroller and H/VScrollbar have MouseWheelEvent listeners. Both use the same redundant code and logic to handle wheel events. Whichever component receives the mouse wheel event (H/VScrollBar) will handle the scrolling and then call preventDefault() on the event to prevent the other components (Scroller) from changing the scroll when it receives the bubbling MouseWheelEvent.

All of the interlocking classes make dealing with scrolling more complex.

Animations & Effects

Mouse wheel scrolling can be animated by setting the "smoothScrolling "style to true and via the "animationDuration" and "easer" properties.

Custom Styles

Default true
Smooth mouse wheel scrolling.

Themes & Skinning

Included is a Spark theme. However, the other themes will use the theme skins for the HScrolbar/VScrollBar so their look will reflect the specific theme.


See the Scroller application for example code.

Back To Top