This post goes over the basics of writing a very simple custom layout that supports virtualization in spark. It assumes that you have already built a custom layout that handles the real (non-virtual) case and are comfortable doing so.
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Sometimes it’s nice to keep an eye on the memory of an application without involving the Flash Builder profiler. This post demonstrates a simple and lightweight component that graphs the value of the Flash Player’s System.totalMemory over time. The chart can be very useful for noticing spikes in memory that might require further investigation with the profiler.
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The default spark List will add a horizontal scroll bar when the contents of the List are wider than its width. This post shows how to change that behavior using a custom item renderer so that a truncation mark like an ellipsis is used instead.
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The ItemRenderer class in Flex 4 has an itemIndex property that was added after beta2. You can use this property within your item renderer to display the row number or index of an item in a spark List.
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ItemRenderer has logic built in that changes between some standard states like normal, hovered, selected, etc. You can supplement this logic by overriding ItemRenderer.getCurrentRendererState(), or do away with the built in states altogether by subclassing DataRenderer instead of ItemRenderer.
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HTML’s select control included a tag called optgroup where you could group items in the drop down together and provide a heading that wasn’t selectable. This post looks at making an equivalent component in Flex 4 by extending DropDownList.
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In spark components, the focusSkin is treated differently from the normal skin. Unlike the skin of a spark component, the focusSkin is not automatically sized or positioned by the component. Instead, it is added as the first child of the component. In addition, if the focusSkin has a property called target, target is set to point to the parent component.
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The VerticalLayout and HorizontalLayout classes now support both the horizontalAlign and verticalAlign properties. This brings the VGroup and HGroup components in line with how the VBox and HBox halo controls worked.
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I recently created a form in Flex that required using multiple DropDownLists with a custom item renderer that loads in preview images of each item. This was really easy to do initially, but I noticed a couple performance issues that bothered me. I decided to improve the performance by implementing a simple caching strategy.
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The spark TitleWindow allows you to drag it around the stage through the use of a skin part called “moveArea”. By attaching mouse handlers to the moveArea, the TitleWindow can be dragged around the screen. In a similar fashion, we can add another skin part called “resizeHandle” to allow the TitleWindow to be resizable.
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