In halo containers you could use the DisplayObjectContainer.contains() method to check if an element is a child, grandchild, great grandchild, … of a given container. This method might not always work as you expect when called on a spark container because not every element in a spark container is a DisplayObject.
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In halo you could add a background color to any container by setting the backgroundColor style, but this is not the case for every spark container. Setting this style on components that extend from SkinnableContainer will work fine, but this style doesn’t exist on the Group component.
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Adding a control bar to a Panel has changed in Flex 4. In halo you would put a mx:ControlBar component as a child of the halo Panel. In spark there is no equivalent ControlBar spark component, but instead a new controlBarContent property exposed on the spark Panel.
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If you have built a custom item renderer for a DataGroup or List you may have come across warnings in your Flash Builder console output similar to this:
warning: unable to bind to property 'firstName' on class 'Object' (class is not an IEventDispatcher)
This post looks at a couple ways of defining a custom item renderer on a DataGroup, but it also applies the same way to a SkinnableDataContainer, spark List, and any other spark components that support item rendering.
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The default spark List skin wraps the the underlying DataGroup with a Scroller component to easily provide scrolling functionality. Custom skinning the Scroller component isn’t very flexible; you can custom skin each scrollbar to change the visuals on them, but you can’t easily reposition them. In these cases it usually makes more sense to get rid of the Scroller and hook up the scrollbars directly.
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It’s easy to delete an item in a spark List from within an item renderer. This is handy if you have a List with a custom renderer that provides a button to delete the item that is associated with that renderer.
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The spark DataGroup component is designed to take data items and pass them through an item renderer to create a visual representation of that data. In Flex 4 it is very easy to build custom item renderers.
This sample application demonstrates how you can create an item renderer that only shows some information by default and allows the user to drill down to see more information by clicking on an item or it’s associated “twisty” icon.
The spark List component in Flex 4 has virtualization enabled by default. Virtualization is an optimization that only renders items that are currently in view which allows the List to support very large data sets. You can learn more about how virtualization works in Flex 4 by reading the Spark Virtualization Spec.
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This sample demonstrates one way of modifying the postLayoutTransformOffsets property of an ItemRenderer in a List in order to have the items appear to zoom in when hovered or selected.
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